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Section A - Executive Summary Research Hub for Fundamental Symmetries, Neutrinos, and Applications to Nuclear Astrophysics: The Inner Space/Outer Space/Cyber Space Connections of Nuclear Physics
Intellectual Merit: The first goal of this proposal is to create a coordinated NSF national theory effort at the nuclear physics core of three of the most exciting “discovery” areas of physics:
◦ Neutrino Physics: Beyond-the-standard model (BSM) physics of neutrinos, including their mixing phenomena on earth and in extreme astrophysical environments; the absolute mass scale and the eigenstate behavior under particle-antiparticle conjugation, and the implication of mass and lepton number violation for cosmological evolution; and the relevance of neutri- nos to astrophysics both in transporting energy and lepton number, and as a probe of the otherwise hidden physics that governs the cores of stars and compact objects. ◦ Dense Matter: The recent start of Advanced LIGO Run 1 could well lead to the observation of the gravitational wave signatures from neutron star (NS) mergers by the end of the decade. This follows the observation of a NS of nearly two solar masses by Shapiro delay, and of “black-widow” systems hinting of even higher masses. Current and anticipated observations provide unprecedented opportunities to determine nuclear matter properties at densities and isospins not otherwise reachable, and to relate them to those we measure in laboratory nuclei. ◦ Dark Matter: Definitive evidence that dark matter (DM) dominates our universe is the second demonstration of BSM physics. Nuclear physics can play an important role in this field by helping direct-detection experimenters understand the variety and nature of the possible responses of their nuclear targets, by connecting the stellar processes we study to the feedback mechanisms that can alter galactic structure, and by contributing to the understanding of composite dark matter in cases where lattice QCD methods are relevant.
These problems pose a common challenge to nuclear physics: the description of fundamental weak interactions in nuclei and nuclear matter, and their embedding in exotic astrophysical environments
- the Big Bang, supernovae (SNe), and NSs – where nuclear microphysics governs the evolution, cooling, transport, and nucleosynthesis. The Hub proposed here will position nuclear physics to play a prominent and also very necessary role in these three discovery areas over the next five years. Astrophysical environments are not only governed by fundamental microphysics, but often pro- vide unique laboratories for probing otherwise untestable aspects of interactions. The first evidence for neutrino oscillations came from models of the Sun. The solar MSW mechanism, the phenomenon fixing the order of two neutrino mass eigenstates, exhibits many new aspects at higher density, influ- encing all flavors and driving novel nonlinear phenomena in SNe. Sterile neutrinos barely coupled to the known neutrinos can have enormous consequences for Big Bang nucleosynthesis. Phases of nuclear matter otherwise inaccessible may influence the properties of NS cores. There is the possibility of determining both the neutrino absolute mass scale and hierarchy from cosmology – with the concordance of the results with future laboratory determinations a matter of exceptional importance. FRIB’s exotic nuclei, so difficult to produce on earth, are present in the ground states of the hot nuclear matter ejected in SNe, and control novel nucleosynthesis. The inner space/outer space/cyber space theme of the proposed Hub describes the synthesis we think can be achieved. Quantitative connections between fundamental symmetries and laboratory tests of those symmetries (inner space), and astrophysical observables such as the electromagnetic and nucleosynthetic signals from a core-collapse (CC) SN or NS merger (outer space), require sophisticated numerical modeling (cyber space). Team organization was guided in part by the desire
to be at the forefront of the needed modeling. The proposed Hub includes experts associated with
- SciDAC efforts in Green’s function Monte Carlo and Lanczos shell model (SM) developments; 2) code suites such as CASTRO/Sedona suitable for integrating CCSNe out to late times; 3) the most advanced nucleosynthesis networks; 4) electroweak nuclear response codes; and 5) stellar evolution codes such as Kepler, MAESTRO, and the Princeton Standard Solar Model, with capabilities that include convection and accretion. Early career researchers affiliated with this proposal are involved in simulating mergers and their gravitational wave signals. We have partnerships with the computational science groups at LBL, ORNL, ANL, and UCSD, hold INCITE grants, and have experience with machines such as Cori, Edison, Titan, Mira, Vulcan, and BlueWaters. Some of the group’s codes are in the current DOE ASCR competition for exascale development. The Hub’s focus will complement, not duplicate, similar collaborations. The DOE is establishing a fundamental symmetries topical collaboration that will focus on matrix element calculations for neutrinoless double beta decay, extracting constraints on CP-violation from electric dipole moment (edm) measurements, and hadronic parity nonconservation (HPNC), work important to ββ decay experiments, the HPNC program at the SNS, and nedm. The DOE SciDAC3 porfolio includes two very relevant projects, the lattice QCD collaboration CalLAT (HPNC in few-nucleon systems) and the USQCD/BSM collaboration (lattice methods for QCD-like composite DM theories). Our physics focus and experimental connections are largely distinct: FRIB (neutron rich nuclei in explosive nucleosynthesis), JLab (including the PREX/CREX test of the nuclear symmetry energy), and proposed neutrino beam experiments (including the DUNE target response, the DUNE SN program, and proposed low-energy solar and coherent neutrino scattering experiments). The Hub’s numerical efforts on modeling SNe, NS mergers, and associated nucleosynthesis fill a gap in the current SciDAC3 nuclear physics portfolio. The Hub can be viewed as the missing piece in a puzzle, that when added, will complete the overall picture. Because Hub members have connections to these other projects, our work will enrich their efforts, and conversely. Many early career researchers are attracted to problems in fundamental symmetries and nuclear astrophysics. The second goal of our Hub is to draw new talent into the field, enhance the nuclear physics training experience through collaborations not normally available to postdocs attached to a single institution, and provide opportunities for interdisciplinary interactions that are often cru- cial to further advancement. The Hub’s “graduating” postdoctoral fellows will not only be expert in their immediate research area, but confident in their ability to interact across boundaries with experimentalists, observers, particle and astrophysics theorists, and computational physicists – and thus to become valued faculty members in a broad-based physics department.
Broader Impacts: Essentially all of the Hub’s resources will be focused on postdoctoral training and career enhancement. The Hub’s design borrows ideas from two very successful efforts, the INT and the Einstein Fellows. The INT has a reputation for producing independent, broadly educated postdocs: its programs provide exposure to a diverse set of subjects and ideas. The NASA Einstein (and Hubble) programs empower postdocs by allowing them to decide where to spend their fellowships, encouraging independence and scientific initiative. The Hub will couple eight sites with three centers, organized to provide a three-year postdoctoral fellow program offering two years of in-depth training at a site followed by a third in an interdis- ciplinary center. The eight sites – Kentucky (Gardner), LANL (Carlson, Cirigliano, Gandolfi), Minnesota (Qian), NC State (McLaughlin), Northwestern (DeGouvea), Notre Dame (Surman) , Ohio U (Phillips, Prakash), and Wisconsin (Balantekin) – are prominent nationally in fundamen-
Section B - Results from Prior NSF support:
A. B. Balantekin
- (a) NSF award numbers: PHY-1205024 and PHY- Amounts: $380,000 and $300, Award periods: 05/01/12-04/30/16 and 08/01/15-07/31/ (b) Titles: Research in Theoretical Nuclear and Neutrino Physics Research Topics in Theoretical Nuclear and Neutrino Physics (c) Summary of results: Merit: These grants support the main theoretical research activity of Balantekin at the interface of nuclear, particle physics and astrophysics. This research led to i) previously unknown symmetries of collective neutrino oscillations and exploration of their consequences in CCSNe; ii) limits on neutrino magnetic moments; iii) elaboration of the impact of the physics beyond the standard model (including neutrino magnetic moments) on BBN; iv) calculation of the neutrino-^13 C cross sections, crucial for achieving a high precision in scintillator based experiments; and v) inclusion of plasma effects on astrophysical reaction rates. Broader Impacts: Virtually all of the work involves collaborations with graduate students that helped them to develop professionally as independent researchers. (d) Publications resulting from the NSF award: So far 39 publications resulted from those grants within the last five years. Representative publications include: ◦ N. Vassh, E. Grohs, A. B. Balantekin and G. M. Fuller, Phys. Rev. D 92 , 125020 (2015) (Majorana Neutrino Magnetic Moment and Neutrino Decoupling in Big Bang Nucleosynthesis [arXiv:1510.00428]). ◦ Y. Pehlivan, A. B. Balantekin and T. Kajino, Phys. Rev. D 90 , no. 6, 065011 (2014) (Neutrino Magnetic Moment, CP Violation and Flavor Oscillations in Matter [arXiv:1406.5489]). ◦ A. B. Balantekin and N. Vassh, Phys. Rev. D 89 , no. 7, 073013 (2014) (Magnetic moments of active and sterile neutrinos [arXiv:1312.6858]).
- (a) NSF award numbers: PHYS-1239053, PHYS-1342611, and PHY- Amounts: $12,000, $12,000, and $12, Award periods: 8/15/2012-7/3/2013, 6/1/2013-7/31/2014, and 03/01/15-02/29/ (b) Titles: Summer Program at CETUP* Center of Theoretical Underground Physics and Related Areas 2015 Summer Program at Center for Theoretical Underground Physics and Related Areas (CETUP)/PPC in Lead/Deadwood, SD (c) Summary of results: Merit: CETUP is intended to be the central collaboration point for long term, intermediate, and programmatic functions for physics and related fields that deal di- rectly with the experimental work being conducted at the underground laboratories. CETUP* is conceived as a forum to get together, to exchange ideas, to discuss recent theoretical results, and debate experimental results and projects. Broader Impacts: Balantekin helped start CETUP* and organized (along with with B. Szczerbinska) all the CETUP* programs that took place at Lead, South Dakota every year since its conception in 2011. The programs have helped pro- fessional physicists, including early career scientists, to develop the scientific connections they need to be successful in this interdisciplinary and rapidly expanding field. (d) Publications resulting from the NSF award: Two proceedings were published resulting form this activity with a third one in preparation.
George Fuller
- (a) NSF award numbers: PHY13-07372 and PHY09- Amounts: $559,633 and $523, Award periods: 09/01/13-08/30/16 and 08/01/10-09/01/ (b) Title: Nuclear, Particle, and Weak Interaction Physics of the Big Bang and Stellar Collapse (c) Summary of results: Merit: These grants support the main theoretical research activity of Fuller at the interface of nuclear and particle physics and cosmology. Key advances from this work include: 1) derivation from first principles of the quantum kinetic equations that provide a complete description of neutrino spin and flavor evolution in dense matter; 2) discovery of a MSW-like level crossing for the neutrino-antineutrino channel, causing significant conversion;
- construction of the BURST code that, for the first time, can couple a full BBN nuclear reaction network with a full Boltzmann multi-energy-bin neutrino transport calculation; and 4) studies of the subtle effects of neutrino mass ionization equilibrium freezeout at the CMB photon decoupling epoch. Broader Impacts: The PI’s research effort is built around the training of students. He has participated in, and organized, summer schools targeting nuclear, particle, and astrophysics graduate students: lectured in the 2012 National Nuclear Physics Summer School, organized (with W. Haxton) the TAUP Summer School at Asilomar in 2013; lectured in and helped organize the 2014 TALENT Summer School at MSU; organized (with J. Primack UCSC) and raised funds for “Neutrino and Nuclear Astrophysics,” the 2014 International Summer School on AstroComputing at the San Diego Supercomputer Center/UCSD. Additionally, the PI is the Chair of the International Advisory Committee for the Center for Nuclear Astrophysics (CNA) at Shanghai Jiao Tong University and helped organize a summer school there. As Director UCSD’s CASS, the PI coordinated the hiring of an Academic Coordinator for Outreach, Karen Flammer. Adam Burgasser (UCSD) and the PI worked with Willie Rockward (Morehouse College) to create the Morehouse-UCSD Bridge Program in Physics, which provides Morehouse students with summer internships at UCSD. The PI supervised one of these students, Jeremy Ariche, in 2014. The PI supervised four successful PhD candidates during the grant period (J. Cherry, W. Misch, A. Vlasenko, E. Grohs), and helped four others start their research careers (Amol Patwardhan, Luke Johns, James Tian, Jung-Tsung Li). (d) Publications resulting from the NSF award: As of this date, 43 publications have resulted from the work: the length of the publication list precludes its inclusion here, but all of the publications are available on the arXiv. The publications in refereed journals include: Physical Review Letters (1), Physics Letters B (1), Physical Review D (13), Journal of Cosmology and Astroparticle Physics (JCAP) (2), Physical Review C (2), Annual Review of Nuclear and Parti- cle Science (1), Astroparticle Physics (1), Progress in Particle and Nuclear Physics (2), Modern Physics Letters (2), and Journal of Low Temperature Physics (1). Recent representative publi- cations include: ◦ N. Vassh, E. Grohs, A. B. Balantekin and G. M. Fuller, Phys. Rev. D 92 , 125020 (2015) (Majorana Neutrino Magnetic Moment and Neutrino Decoupling in Big Bang Nucleosynthesis [arXiv:1510.00428]). ◦ E. Grohs, G. M. Fuller, C. T. Kishimoto, and M. W. Paris, Phys. Rev. D 92 (2015) 125027 [arXiv:1412.6875] ◦ A. Vlasenko, G. M. Fuller, and V. Cirigliano, ”Neutrino Quantum Kinetics,” Phys. Rev. D 89 (2014) 105004 [arXiv:1309.2628]
(c) Summary of results: Merit: This project involved theoretical studies of peculiar SNe believed to be the result of thermonuclear explosions in, e.g., degenerate white dwarf (WD) stars. We carried out simulations of several different scenarios, including models of Type Ia SNe from the merger of two WDs, and the nature of rapidly evolving transients thought to be related to partial explosions of WDs. Our method involved simulating the hydrodynamics and nucleosynthesis in stellar explosions, and modeling the observable light curves and spectra with the radiation transport code SEDONA. Our results have helped clarify the physical origin of both normal and unusual Type I SNe. Broader Impacts: The grant was largely used to support graduate and undergraduate students and postdocs, furthering the training of early career scientists. The PI was co-director of the UC High Performance AstroComputing Center Summer School in 2011, which presented material related to this project. The PI recently had a popular article accepted for publication in Scientific American, which describes some of the topics studied under this project, and has also written a related pedagogical chapter on “Peculiar Supernovae” to appear in the Supernova Handbook, a book aimed at helping graduate students entering the field. (d) Publications resulting from the NSF award: So far 10 refereed publications have resulted from this grant. Representative publications include: ◦ J. Bloom, D. Kasen, et al.,“A compact degenerate primary-star progenitor of SN 2011fe”, Astrophysical Journal, p. 17, vol. 744, (2012). ◦ K. Shen, L. Bildsten, D. Kasen and E. Quataert, “The long term evolution of double white dwarf mergers”, Astrophyiscal Journal, p. 35, vol. 748, (2012). ◦ C. Raskin, D. Kasen et al., “Type Ia Supernovae from Merging White Dwarfs. II. Post-merger Detonations?, ApJ, 788, 75 (2014).
M. Prakash
- (a) NSF award number: AST - 0708284 Amount: $270, Award period: 09/01/2007 - 08/31/2011 (3 year award - 1 year no cost extension) (b) Title: The Hydrodynamical Histories of Elliptical Galaxies (c) Summary of results: Merit: The PI replaced astronomer T. S. Statler during the period he was NSF program officer. Projects goals focused on achieving a better understanding of the effects of the energetics of supermassive black holes in the centers of galaxies on galaxy evolution and galaxy properties. The evolution of isolated elliptical galaxies, interacting elliptical galaxies, and merging spiral galaxies were simulated, employing different models for black hole energetics in order to access their consequences for galactic structure. Broader Impacts: The grant supported the doctoral dissertation work of a graduate student, who concentrated on the gas-dynamical simulations described above. The supported student had a change of career goals late in the period of support, finishing with a Master’s degree. (d) Publications resulting from the NSF award: ◦ Diehl, S. et al., “Generating Optimal Initial Conditions for Smooth Particle Hydrodynamics Simulations”, Publications of the Astronomical Society of Australia (2015); arXiv: 1211.0525v ◦ Statler, T. S. 2012, “Hot Gas Morphology, Thermal Structure, and the AGN Connection in Normal Elliptical Galaxies,” in “Hot Interstellar Matter in Elliptical Galaxies,” ed. D.-W. Kim and S. Pellegrini, Springer ASSL series #378, pp. 207 - 234.
Section C - Hub Description
Overview: The Hub research program will position nuclear physics to play an important and necessary role in three of the most exciting discovery areas in fundamental physics, the novel flavor physics of neutrinos, the nature of the dense nuclear matter that governs the structure of NSs and the core bounce of SNe, and the nature of the DM that dominates our universe. The nuclear physics of these three problems involves a common theme, the description of fundamental weak interactions in nuclei and nuclear matter, and their embedding in exotic astrophysics environments, where they control the cooling, the transport of energy and lepton number, and the nucleosynthesis. Hub research will connect the nuclear microphysics to the astrophysics, further developing the numerical tools required to treat weak interactions under extreme conditions as well as those needed to model the astrophysical environments producing those conditions. By engaging young researchers in this program, we hope to produce a new generation of researchers who are both deep and broad – skilled in the nuclear microphysics, while aware of its relevance to a range of astrophysical problems. The physics flows in both directions: a SN cannot explode unless microscopic processes trans- port the energy released in CC preferentially to the mantle, allowing ejection of material that was previously bound. Hydrodynamic compression, shock creation and propagation, storage of gravi- tational energy in a leptonic sea, and transport of that energy by neutrino processes all play key roles in one of Nature’s most important nucleosynthetic factories. Decades of work have led to the present state of the art, high fidelity 3D calculations with realistic microphysics that can follow dynamic explosions out to times of ∼ 1 sec. A theme of our Hub will be to connect the conditions at 1 sec to the electromagnetic and nucleosynthetic observables from much later times – which re- quires a different set of radiative transport codes of the type members of our Hub have developed. Conversely, the conditions Nature generates in such an explosion are so exotic that they depend on aspects of fundamental physics that may otherwise be hidden from us. Perhaps the most extraor- dinary example is DM – the gravitational “glue” through which structure forms, so far detected only via its critical role in shaping our universe, and without which we would not have a Milky Way to study. The neutrino physics which led to this year’s Nobel Prize – which requires extensions of our standard model to include massive neutrinos and their flavor mixing – becomes far more exotic at the core of a SN, where novel nonlinear phenomena can radically alter both flavor and lepton number. One also encounters extremes in the hadronic physics. Our FRIB experimental colleagues are working diligently to approach the neutron drip line, where they will be rewarded by the oppor- tunity to study rare isotopes, but only for the instant before they retreat to the valley of stability. But in high-density astrophysics, neutron-dominated matter is often the ground state, allowing us to study over long times the consequences of isospins and densities unreachable on earth. Already observations of NS masses have greatly constrained the nuclear equation of state; with the recent discovery and the continued monitoring of binary pulsars, and the anticipated merger signals that Advanced LIGO might detect, a great deal more may be learned. This confluence of inner and outer space, which can be quantitatively linked in our theoretical work because of the power of modern computer simulations, is the theme of our Hub. We see this as a marvelous area for training postdocs, who can develop a “toolbox” of specific nuclear physics skills that can then be applied to a variety of important, interdisciplinary astrophysical problems. As Fig. 1 conveys, a postdoc who learns state-of-the-art nuclear structure techniques to evaluate electroweak responses important to neutrino-driven nucleosynthesis in a SN, for example, can pivot in a moment to calculate DM direct-detection scattering cross sections. In fact, our much more mature understanding of the former may allow that postdoc to make important conceptual contri-
The Hub centers are
Berkeley Wick Haxton Dark Matter, Neutrinos Dan Kasen Nucleosynthesis, SN/NS Modeling San Diego George Fuller Neutrinos, Nucleosynthesis W ashington Jim Lattimer Dense Matter, Neutrinos Sanjay Reddy Dense Matter, Neutrinos
One of the roles of the centers is to give postdocs an opportunity to work in groups with espe- cially active visitor programs, so that they will have opportunities to form collaborations across boundaries, if so inclined. The three centers have somewhat different characters. Berkeley has a large Theoretical Astrophysics Center (16 faculty) and a great deal of activity there and at LBL in high performance computing applications to astrophysics and cosmology. The San Diego center will be part of CASS, the Center for Astrophysics and Space Sciences, a multidisciplinary campus unit involved in several high-profile observational efforts; there are connections to the San Diego SuperComputer Center, as well. Washington, because of the INT, is the most active nuclear theory visitor center in the US, and can provide Hub postdocs with opportunities to interact with other segments of our field and to take part in INT programs. Several of our colleagues have agreed to be “affiliated scientists” of the Hub, not responsible for the Hub’s proposed research, but available as long-time collaborators of the senior investiga- tors, to share their expertise with the postdocs. They include Ann Almgren and John Bell, LBL (applied mathematicians involved in the development of the MAESTRO/Castro/Sedona suite for SN physics); Francois Foucart, Philipp Moesta, and Sasha Tcheckhovskoy, Berkeley/LBL (Einstein Fellows involved in numerical simulations of mergers and related numerical astrophysics); Alexan- der Heger, Monash University (stellar evolution with Kepler); Calvin Johnson, San Diego State and CASS (developer of the highly parallelized SM code Bigstick); Matt Kistler, KIPAC/SLAC (DM in- direct signals); Gabriel Martinez-Pinedo, TU-Darmstadt (nuclear reaction input for the r-process); Bernhard Muller, Queen’s University, Belfast (3D SN simulations); Filomena Nunes, MSU (FRIB theory users group, reactions); Achim Schwenk, TU Darmstadt (DM nuclear response functions); Aldo Serenelli, Barcelona (standard solar model); Fridolin Weber, San Diego State and CASS (NS structure); and Pavlos Vranas (LLNL) and Andre Walker-Loud (LBL) (lattice QCD theorist con- nected with the fundamental symmetries efforts of the USQCD/BSM and CalLAT collaborations). Further information is given in Sections F and G. Most of these individuals are connected with one of the three Hub centers, where they might become involved in collaborations involving the Hub postdocs.
Resources available: The nuclear physics groups involved in this proposal can accommodate the day-to-day needs of theorists, e.g., office space, visitor accommodations, local computing clusters, etc. As noted previously, several members are involved in SciDAC/INCITE collaborations: the group’s access to high performance computing and supporting computer science is outstanding, due to facilities such as NERSC and SDSC, LANL computing, etc. We have access to modern high-definition video streaming equipment. This will not only be used in site-to-site collaborations, but will also allow us to broadcast seminars. Our plan is to try to schedule e-seminars once a month, as a way to make sure the entire group gathers regularly to hear about progress, and to plan further steps.
Interactions with other groups: Our group includes two members that are also involved with the recently created Topical Collaboration on double beta decay matrix elements and fundamental symmetries (particularly, electric dipole moment measurements). While the work proposed here and by the TC membership has little direct overlap, there are important underlying themes– neutrino mass, lepton number, CP violation – connecting the two efforts. The workshops we will host at the time of our annual meeting will provide a good opportunity to engage members of the TC. We have close connections to the two lattice QCD efforts most relevant to symmetries. The BSM group – which works on topics such as the structure of composite DM and the neutron edm – is led by one of our affiliates, P. Vranas, and includes participants from Berkeley and Los Alamos. The Berkeley/LBL/LLNL CalLAT group’s work focuses on hadronic parity violation, but includes topics like the form factor dependence of gA(q^2 ) relevant to our work on weak responses. Our members interact frequently with both collaborations, and the Hub will seek their participation in our annual meeting. NSF supports a Theoretical and Computational Astrophysics Network (TCAN) with major nodes at the California Institute of Technology, Syracuse University, Cornell University, and the University of Washington, one of our Hubs. Reddy is the UW lead. The Network’s goal is to advance the theory of merging compact-object binaries and stellar collapse. Gravitational waves from these types of events are expected to be detected by Advanced LIGO in coming years. The network team’s goals are to develop the theoretical and computational tools needed to extract the equation of state of dense nuclear matter from gravitational wave and electromagnetic observations, and to determine the impact of compact-object mergers on the synthesis of light and heavy elements. This project has perhaps the most direct connection to the Hub’s goal. Its goals include (1) development of an open- source, next-generation relativistic astrophysics computation framework; (2) improvements in the theoretical understanding of the nuclear equation of state; (3) improvements in the computational treatment of nuclear reactions in merger and collapse simulations; and (4) developing strategies for extracting EoS information from multi-messenger observations. There are abundant opportunities for collaboration between the Hub and TCAN.
Hub Science
Neutrinos and Nucleosynthesis - Overview: Three of the most exciting developments in physics and astrophysics have converged to make neutrino physics an extraordinarily exciting dis- covery area. First, solar and atmospheric neutrino discoveries, now augmented by a new generation of laboratory and accelerator beam experiments, revealed that our standard model of elementary physics was incomplete, opening up a series of new questions about neutrino mass, flavor, and CP properties. Second, recent and anticipated advances in the capabilities of electromagnetic, neu- trino, and gravitational wave (“multi-messenger”) probes of compact objects and cosmology have given us a new set of neutrino laboratories, ones creating extremes of density, temperature, lepton number, and isospin impossible to realize on earth. Third, the rapid advance to exascale comput- ing has given us the tools we need to connect astrophysical events to the underlying microphysics, including fundamental neutrino properties. Neutrinos are inordinately important in astrophysics, transporting most of the energy, entropy, and lepton number in environments like collapsing SN cores, merging NSs, and the early universe, while controlling the isospin of the matter through conversions between protons and neutrons. The specific p/n ratio neutrinos imprint on the matter is crucial to subsequent nucleosynthesis, which
to known laboratory conditions. Although the modernization of such input could be considered “yeomans work,” improvements in such data bases are as important to nuclear astrophysics as a foundation is to a well-constructed building. The theory and computational issues are not routine. Bigstick [3], which was developed cooper- atively by the SciDAC2 UNEDF collaboration and members of our team under SciDAC3, is capable of untruncated SM calculations through most of the g 7 / 2 sdh 11 / 2 space. We now have highly tuned and remarkably predictive effective interactions that, if used in untruncated spaces, give reliable low-momentum representations of wave functions. An example of the state-of-the-art is GCN [4]. Just as zero-temperature inclusive responses can be calculated using Lanczos moments methods (thus avoiding impractical state-by-state summations), there exist finite-temperature extensions of these methods – though some of the approaches, developed in other subfields [5], have not yet been employed in nuclear physics. The theoretical issues connected with properly defining the partition function are nontrivial: the SM Slater determinant basis, despite its compactness, is in principle complete, so double-counting issues arise if that response is combined naively with those for continuum states such as (A − 1 , Z) + n, for example. Finally, the computer science issues are interesting, due to the combination of SM capabilities allowing full-space calculations, interactions like GCN5082 that are applicable to large libraries of nuclei without nucleus-by-nucleus tuning, and density matrix techniques to extract from the SM results just that information needed to evaluate one-body operators. It should be possible to automate calculations, so that the theorist’s time can be invested in the high-level conceptual issues listed above, instead of tedious input-file preparation. The moments technique is immediately applicable to allowed and first-forbidden operators that dominate nuclear responses for neutrino energies typical of SNe, where Tν. 6 − 8 MeV (Eν ∼ 3 Tν ). A method for treating the full momentum transfer dependence of response functions has been de- veloped [6], should we decide such an extension is necessary. One needs, in addition to charged and neutral-current neutrino reactions important for ν- and r−process nucleosynthesis, β decay and free- and bound-electron capture rates, as well as neutral current (neutrino pair) decay of excited nuclei. Past experience shows that improved weak rates can have a significant effect on SN quantities such as the trapped lepton fraction and mass of the homologous core [7, 8].
Neutrino flavor (and spin) evolution in dense matter: The proper treatment of neutrino flavor and spin evolution in explosive astrophysical environments requires the solution of quantum kinetic equations (QKEs) [9, 10, 11, 12, 13]. As general QKE solutions in multi-D environments are currently impractical, researchers have followed an apparently reasonable procedure: separation of regimes and techniques, with 1) Boltzmann neutrino transport at high density (e.g., below the neutrino sphere) where scattering-induced de-coherence dominates and neutrino oscillations are neglected, and 2) coherent, flavor evolution treatment at lower density. In the latter case, a system of ∼ 108 nonlinearly-coupled Schr¨odingier-like equations can be solved on a supercomputer, with the nonlinearity stemming from the neutrino-neutrino forward scattering contribution to the potential governing flavor transformation. The results are startling: collective neutrino flavor oscillations and their manifestations like the swap/split occurring for a host of conditions potentially relevant for the SN signal and nucleosynthesis [14, 15, 16, 17, 18, 19, 20, 21]. However, this separation of coherent, flavored evolution and incoherent Boltzmann regimes is not valid [22] in some SN epochs, such as the shock breakout neutronization pulse and the iron core CC accretion phase. Even a small amount of direction-changing scattering, e.g., one neutrino in 103 , can completely alter flavor evolution, converting the flavor evolution problem from an initial
value problem into something more akin to a boundary value problem, with scattering facilitating quantum flavor information propagating downward from higher radii. This “halo” of scattered neutrinos (see Fig. 2) also renders flavor evolution dependent on nuclear composition, as coherent neutrino-nucleus scattering varies as the square of the nuclear mass number. This couples flavor evolution to nuclear equation of state physics in a new way. This result led to a derivation of the full QKEs from first principles and the discovery of a surprising way that Majorana neutrinos and antineutrinos can transform into each other (spin flip) in anisotropic media [24, 25, 26, 27, 28].
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Figure 2: Left: The color scale indicates the density during the accretion epoch for a 15 M progenitor CC SN 500 ms after core bounce [23]. Right: Effect of the scattered neutrino halo for the matter distribution to the left. The color scale indicates the ratio of the sum of the maximum (no phase averaging) magnitudes of the constituents of the neutrino- neutrino Hamiltonian, | Hˆbulb νν | + | Hˆ ννhalo |, to the contribution from the neutrinosphere | Hˆbulb νν |.
Neutrinos can transform their flavors and/or spins via medium-affected coherent neutrino os- cillations, and they can do this through scattering as well. Insight into the QKE’s may help with two related issues: (1) Sound waves, shocks, and turbulence can induce non-adiabatic jumps in neutrino flavor survival probability [29] or flavor de-polarization [30, 31, 32, 33, 34]; and (2) Co- herent treatments of the neutrino flavor field suggest that there may be no steady state solutions [35, 36, 37]. While solving for neutrino flavor/spin evolution is difficult, solutions are necessary to make contact with important observables such as the CCSN neutrino signal in DUNE and SN nucleosynthesis. Another important goal is a full QKE treatment of the early universe, to make contact with BBN and CMB neutrino physics constraints.
Nucleosynthesis: The SN neutrino-driven wind is thought to be an important galactic source of nuclei above the iron group. The quantity that most directly determines the resulting nucle- osynthesis is the neutron-to-proton ratio, set by weak interactions in the wind. As the proto-NS deleptonizes, electron neutrino emission dominates first, initially driven the material to the proton- rich side. These early neutrino-driven winds are thus an attractive potential site for the νp-process [38, 39, 40, 41]. At somewhat later times (∼ seconds), the proto-NS cools via emission of roughly equal numbers of neutrinos in all flavors. If the electron antineutrinos emerge from deeper within the proto-NS and thus at higher energies than the neutrinos, the material can become (modestly) neutron rich. Early calculations suggested the neutrino heating could produce entropies sufficient to sustain a vigorous r-process [42, 43], though problems with this conclusion quickly emerged [44, 45, 46]. While conditions producing the heaviest r-process nuclei are not found in modern simulations [47, 48, 49, 50, 51], the inclusion of new neutrino physics can alter this conclusion [52, 53, 54, 55]. In any event, as the SN neutrino-driven wind is expected to eject ∼ 10 −^3 solar masses of material per event to the interstellar medium [56], its composition is of great importance to galactic chemical evolution and nucleosynthesis studies. Our calculations of neutrino transport, oscillations, and nucleosynthesis will not only provide the state-of-the-art characterization, but also
neutrino emission, SN conditions change. Accretion influences some of the early neutrino emission. As the emission continues, the core lepton number is reduced, potentially triggering a change in the nuclear-matter phase or even a delayed collapse to a BH. At late times the shock wave may pass through the first MSW resonance, altering the density and thus the flavor conversion. It has also been shown that convection driven by hydrodynamic instabilities - the SASI mode – can imprint high frequency (few msec) fluctuations [81] on the neutrino flux, potentially detectable by comparing two high-statistic detectors (SuperKamiokande/IceCube/DUNE). Thus, in addition to the information about the global properties of the SN – the total energy and lepton number radiated – the neutrino flux carries a great deal of information about SN dynamics. Though we think of the neutrino burst as prompt, future observations will continue far beyond the times modeled in our most advanced 3D explosion codes. Typically simulations extend to ∼ 1 sec after core bounce, when it may become apparent that a successful explosion has been launched. Our main interest in multi-messenger SN physics – what we find missing – is the bridge from 1 sec to the late time observables, which includes the long time development of the neutrino burst, but also the much later electromagnetic and nucleosynthetic signals. The Hub program we envision – some of this issues are relevant to NS merger outflows, as well – is the use of sophisticated radiative transport codes like Sedona to establish this bridge. Such codes can accept results from an explosion calculation as initial conditions, propagating the explosion forward in a less detailed but more efficient way. Important questions might then be answered. How does mantle ejection reflect the strength of the explosion at 1 sec? What determines the strength and duration of the kinetic and optical displays? What connection exists between early convection and the inhomogeneous distribution of elements like Ni and Ti in the ejecta? One of the most important clues we have about the origin of the nuclei in our galaxy comes from the fossil evidence of early nucleosynthetic events, preserved on the surfaces of old, metal-poor halo stars. These “museums” are an important part of the multi-messenger story because they preserve data from a time when the galaxy was unmixed – data on the contributions of individual events to the r-process. We know from such stars that r-process nucleosynthesis was already underway when the galaxy contained only 0.01% of the metals it has today. The similarity of the r-process patterns seen in these stars to that seen in the sun is striking. Part of the r-process puzzle is to explain these early events – forensic evidence suggests a SN association – in view of our difficulties in producing a robust r-process in current SN explosion models. One idea Hub members have pursued is a SN r-process that is successful only at low metallicity: a weak neutron source can then drive an r-process, since the critical parameter is the neutron/seed ratio, and there are few seeds. A neutrino-driven mechanism has been identified in the He zones of metal poor stars [82]. While such a mechanism might account for the metal-poor star data, other more robust mech- anisms would need to account for the bulk of galactic metal. NS mergers may be the major source for heavy elements with mass numbers above 130 including the actinides. The decay of the radioac- tive progenitors for these elements can power a unique infrared light curve that might have been observed – if confirmed, this “kilonova” would be the first direct evidence identifying an r-process site [83]. In addition, NS mergers are also the leading candidate for producing short gamma-ray bursts. The accretion disks in these events may contribute additional elements with mass numbers below 130. Last but not the least, NS mergers are a major source for gravitational waves. The wave form may help constrain the equation of state of dense matter, which is crucial in determining the amount of material dynamically ejected with freshly-synthesized nuclei during the merger.
The Near-Field Cosmology Connection: The standard cosmology based on cold dark matter (CDM) and dark energy explains a wide range of observational data, including structures on scales of galaxy clusters and larger. However, difficulties arise at the galactic scale. As a result of hierarchical structure formation, the CDM halo associated with a main galaxy has many sub-halos. In principle, this can account for the dwarf satellite galaxies orbiting the Milky Way. However, the number of observed satellite galaxies is far below that predicted in simulations, leading to the “missing satellite” problem. In addition, the largest sub-halos appear unsuitable for hosting the brightest Milky Way satellites because of incompatible mass distributions - the so-called “too big to fail” problem. These problems may reflect an incomplete treatment of baryons and the associated gas dynamics in CDM simulations, issues closely connected to the nucleosynthesis and chemical evolution studies of the Hub: baryonic processes are expected to alter the CDM distribution through various feedback mechanisms, especially the redistribution of gas, and hence CDM via gravitational interaction, by SN explosions. However, an ab initio treatment of the feedback in simulations is daunting if not impossible because the relevant gas physics is both complicated and poorly understood. Consequently, various empirical approaches are taken in simulations to describe gas accretion by CDM halos, cooling and condensation of gas to form stars, conversion of cold into hot gas by radiation and SN explosions, and gas expulsion from halos. These processes also determine the mixing and chemical enrichment of gas. Consequentially, the chemical evolution of dwarf galaxies, reflected in the elemental abundances of the stars that have formed through today, in principle constraint any approximate treatment of the gas and baryons. Nuclear physicists, by understanding the nuclear processes that drive chemical evolution, are making important contributions to our understanding of standard CDM cosmology. Star formation histories and elemental abundances in MW satellite galaxies have become the major objectives of observational near-field cosmology. Available data have already provided important insights into the gas dynamics and chemical enrichment of these systems. By combining our understanding of nuclear microphysics at the stellar scale with observations at the galactic scale, major advances can be made in understanding the TBTF problem in particular and galaxy formation and evolution in general.
Solar Neutrinos: Our much improved understanding of neutrino flavor physics allows us to return to the question that started neutrino astrophysics: can we use neutrinos to test our understanding of our nearest star? Next-generation solar neutrino experiments are envisioned with counting rates of tens of thousands of events per year and extraordinary radio-purities, mounted at depths of two kilometers. Important open questions could be addressed:
- The most precisely known spectrum of neutrinos in Nature are those from solar p+p β decay, known to a precision of ∼ 0.4% [84, 85]. Main sequence stellar evolution is based on the assumption of hydrostatic equilibrium, though physics allows secular variations in stars on the Kelvin timescale. The most direct test of this assumption would come from a comparison of the (instantaneous) p+p neutrino flux with the (delayed) surface photon luminosity. Equivalence of these two fluxes would test solar variability of potential interest to long-term climate change, as well as any candidate BSM stellar cooling mechanism.
- A second fundamental assumption of the standard solar model (SSM), a homogeneous zero- age Sun, is in question. This assumption comes from the predicted convective mixing of the collapsing gas cloud in the pre-solar Hayashi phase. However, the “solar metallicity problem,”
role [105, 106, 107]. We will build on recent efforts to include chiral EFT two- and three-nucleon potentials into QMC calculations of neutron matter [108, 109, 110], exploring their influence on the properties of NSs (radii, maximum mass, crust thickness, tidal polarizability, etc.). These calculations will be combined with constraints from measurements of the neutron skin thick- ness [111, 112, 113], dipole polarizability [114], nuclear masses, and the range of observed NS radii as determined in a Bayesian framework (see also below) [115]. All of this information will be used to develop a minimal Hamiltonian with density dependent effective two-body interac- tions with a finite range for use in astrophysics. The work will also inform density functional theories of heavy nuclei [116]. We will develop a hybrid model based on second-order perturba- tion theory where the parameters of this simpler Hamiltonian are determined to reproduce the EoS of pure neutron matter, its spin and isospin susceptibilities obtained from ab intio QMC calculations with realistic two- and three-body forces, and the empirical properties of symmetric nuclear matter. We will use the Bayesian formalism developed in Refs. [117, 115] to obtain intervals for the parameters in the effective interaction (and correlations between them) that reflect the uncertainties of input observables used in the fitting. We will therefore be able to use the effective interaction to propagate uncertainties in, e.g., the EoS, to any quantity computed within our framework. This approach will complement ongoing efforts to develop an EoS of isospin asymmetric matter based on many body perturbation theory and chiral EFT interac- tions [118, 119]. The approach should more cleanly isolate those aspects of the nucleon-nucleon (NN) interaction most relevant to the thermodynamic properties of astrophysical dense matter. Although the discovery of two massive NSs with masses M & 2 M [120, 121] disfavors strong first-order phase transitions at supra-nuclear density, it remains likely that non-nucleonic degrees of freedom will emerge well above saturation density. With an improved EoS of neutron-rich matter that extrapolates to high density [122], we can explore correlations between the NS radii, the maximum mass, slope of the mass-radius curve for canonical NS masses in the range 1.2-1.4 M , deriving quantitative constraints on possible phase transitions at high density.
- Thermal properties of dense matter: In SNe and NS mergers, the temperature is controlled by the specific heat of dense, partially degenerate matter. The temperature in turn influences many aspects of the evolution as neutrino and weak interaction rates are strong functions of the ambient temperature [123]. EoSs in current use are based on mean field approaches that neglect important contributions to the specific heat from correlations and fluctuations. We propose two new approaches. First, we will extend the hybrid approach discussed earlier to finite temperatures to build a new EoS for astrophysics which naturally incorporates some of these effects. Second, we will study a series of effects known to strongly influence the specific heat of interacting Fermi systems, including the enhancement of the nucleon effective masses at the Fermi surface, coupling between quasi-particles and collective excitations, and the non- analytic behavior of the nucleon self-energy [124, 125]. Some of these effects have been studied using many-body perturbation theory and self-consistent Green’s Function methods in recent years [126, 127, 118, 128, 129, 130]. The proposed research will improve the state of the art by: (i) developing Monte Carlo techniques for nuclear systems at finite temperature; (ii) using Fermi liquid theory with l = 0, 1 Fermi liquid parameters calculated from ab initio methods to estimate the non-analytic T 3 log T contribution to the specific heat at low to intermediate temperatures which are known to play a role in 3 He [124, 131]; (iii) investigating the role of thermal pions; and (iv) including collective excitations at very low temperatures where the single-particle degree of freedom is frozen due to BCS pairing and/or strong Coulomb correlations between ions [132].
- Bremsstrahlung, neutrino scattering and absorption, and related processes in dense matter: In dense matter, the thermal production of μ and τ neutrinos, as well as axions, dark photons and other DM candidates, is dominated by NN bremsstrahlung; the inverse processes are important for neutrino pair absorption and inelastic neutrino scattering [133]. Most calculations of these rates are either based on a simplified treatment of the NN interaction [134] or on the soft- radiation approximation [135]. Building on recent work in Refs. [136, 137] and using chiral EFT potentials and associated two-body currents, we will go beyond the soft-radiation approximation. We will study screening due to long-range correlations and the Landau-Pomeranchuk-Migdal suppression of soft-neutrino emission due to finite quasi-particle lifetimes [138, 139, 140, 141]. This work will give us more reliable estimates of the thermal production of weakly interacting particles. We will pursue a novel approach to the low-energy nuclear response functions relevant to neutrino scattering and absorption in hot and dense matter. Building on earlier work based on Landau’s Fermi liquid theory and the Random Phase Approximation [142, 143, 144, 145, 146], the energy dependence of response functions will be represented by well-motivated parameterized forms that can be adjusted to fit exact QMC results for the imaginary time response and sum rules as outlined in Ref. [147]. This will allow us to incorporate contributions from single- and multi- particle excitations, as well as from collective modes in the low-energy spectrum. The improved microphysics will be incorporated into codes being developed to model NS mergers and SNe at UC Berkeley, providing a starting point for more realistic treatments of neutrino flavor transformations in these extreme environments by Hub members at UC San Diego, U of Wisconsin and NCSU. Jointly, we will design a suite of simulations to address how microphysics influences the GW emission, composition of the ejecta, and electromagnetic emissions from NS mergers, and neutrino emission from SNe. The low-energy response of nuclear matter is also relevant in the context of DM interactions with large finite nuclei and aligns well with other DM research at UC Berkeley and at the U of Kentucky [148]. Issues relating to two-particle-hole excitations and axial two-body currents which play a role in bremsstrahlung processes, and possibly in the quenching of the axial charge, are of interest also to neutrino-nucleus reactions[149, 150, 151] and to double beta-decay [152, 153], and can play a role in inelastic DM nucleus scattering. Understanding and estimating errors associated with the EoS and weak interaction rates will be a major component of all three dense matter research thrusts. Using a Bayesian framework and, where appropriate, EFT [117, 154] as a guide, we will evaluate the impact of uncertainties on EoS, neutrino opacities, emissivities etc., while also delineating the mapping from correlated observables and their uncertainties to model parameters.
Dark Matter in Nuclear Physics: Various observations establish that most of the matter in our universe is dark, long-lived or stable, warm or cold, gravitationally active, and without strong interactions with ordinary matter [155, 156, 157]. DM represents new physics, beyond the standard model, with candidates including new weakly interacting massive particles (WIMPs), axions, sterile neutrinos with keV-MeV masses, and hidden-sector composites that might be dark analogs of pions or nucleons. The Hub investment in this area is driven by our concern that DM astrophysics is inextricably part of coupled galaxy/nucleosynthesis/explosive astrophysics/microphysics issues discussed so far in this proposal, and that the absence of adequate nuclear physics involvement is holding back the
