arXiv subjects

George M. Fuller

Publications and source records attributed to George M. Fuller.

At least 91 records · Page 5Linked to original sources

arXiv2007

Sterile Neutrino-Enhanced Supernova Explosions

We investigate the enhancement of lepton number, energy, and entropy transport resulting from active-sterile neutrino conversion $ν_e\toν_s$ deep in the post-bounce supernova core followed by re-conversion $ν_s\toν_e$ further out, near the neutrino sphere. We explicitly take account of shock wave and neutrino heating modification of the active neutrino forward scattering potential which governs sterile neutrino production. We find that the $ν_e$ luminosity at the neutrino sphere could be increased by between $\sim 10 %$ and $\sim 100 %$ during the crucial shock re-heating epoch if the sterile neutrino has a rest mass and vacuum mixing parameters in ranges which include those required for viable sterile neutrino dark matter. We also find sterile neutrino transport-enhanced entropy deposition ahead of the shock. This `` pre-heating\rq\rq can help melt heavy nuclei and thereby reduce the nuclear photo-dissociation burden on the shock. Both neutrino luminosity enhancement and pre-heating could increase the likelihood of a successful core collapse supernova explosion.

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arXiv2007

Stellar Collapse Dynamics With Neutrino Flavor Changing Neutral Currents

We perform one-zone simulations of the infall epoch of a pre-supernova stellar core in the presence of neutrino flavor changing scattering interactions. Our calculations give a self-consistent assessment of the relationship between flavor changing rates and the reduction in electron fraction and re-distribution of initial electron lepton number among the neutrino flavors. We discuss and include in our calculations sub-nuclear density medium corrections for flavor changing scattering coherence factors. We find that flavor changing couplings epsilon > 3x10^(-4) in either the electron neutrino - muon neutrino or electron neutrino - tau neutrino channels result in a dynamically significant reduction in core electron fraction relatively soon after neutrino trapping and well before the core reaches nuclear matter density.

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arXiv2007

Analysis of Collective Neutrino Flavor Transformation in Supernovae

We study the flavor evolution of a dense gas initially consisting of pure mono-energetic $ν_e$ and $\barν_e$. Using adiabatic invariants and the special symmetry in such a system we are able to calculate the flavor evolution of the neutrino gas for the cases with slowly decreasing neutrino number densities. These calculations give new insights into the results of recent large-scale numerical simulations of neutrino flavor transformation in supernovae. For example, our calculations reveal the existence of what we term the ``collective precession mode''. Our analyses suggest that neutrinos which travel on intersecting trajectories subject to destructive quantum interference nevertheless can be in this mode. This mode can result in sharp transitions in the final energy-dependent neutrino survival probabilities across all trajectories, a feature seen in the numerical simulations. Moreover, this transition is qualitatively different for the normal and inverted neutrino mass hierarchies. Exploiting this difference, the neutrino signals from a future galactic supernova can potentially be used to determine the actual neutrino mass hierarchy.

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arXiv2006

Collective Neutrino Flavor Transformation In Supernovae

We examine coherent active-active channel neutrino flavor evolution in environments where neutrino-neutrino forward scattering can engender large-scale collective flavor transformation. We point out a key quantity, the "total effective energy", which is conserved in several important regimes. Using this concept, we analyze collective neutrino and antineutrino flavor oscillation in the "synchronized" mode and what we term the "bi-polar" mode. We thereby are able to explain why large collective flavor mixing can develop on short timescales even when vacuum mixing angles are small in, e.g., a dense gas of initially pure $ν_e$ and $\barν_e$ with an inverted neutrino mass hierarchy (an example of bi-polar oscillation). In the context of the spin precession analogy, we find that the co-rotating frame provides insights into more general systems, where either the synchronized or bi-polar modes could arise. For example, we use the co-rotating frame to demonstrate how large flavor mixing in the bi-polar mode can occur in the presence of a large and dominant matter background. We use the adiabatic condition to derive a simple criterion for determining whether the synchronized or bi-polar mode will occur. Based on this criterion we predict that neutrinos and antineutrinos emitted from a proto-neutron star in a core-collapse supernova event can experience synchronized and bi-polar flavor transformations in sequence before conventional Mikhyev-Smirnov-Wolfenstein (MSW) flavor evolution takes over. This certainly will affect the analyses of future supernova neutrino signals, and might affect the treatment of shock re-heating rates and nucleosynthesis depending on the depth at which collective transformation arises.

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arXiv2006

Coherent Development of Neutrino Flavor in the Supernova Environment

We calculate coherent neutrino and antineutrino flavor transformation in the supernova environment, for the first time including a self-consistent treatment of forward scattering-induced coupling and entanglement of intersecting neutrino/antineutrino trajectories. For the atmospheric neutrino mass-squared difference we find that in the normal (inverted) mass hierarchy the more tangentially-propagating (radially-propagating) neutrinos and antineutrinos can initiate collective, simultaneous medium-enhanced flavor conversion of these particles across broad ranges of energy and propagation direction. Accompanying alterations in neutrino/antineutrino energy spectra and/or fluxes could affect supernova nucleosynthesis and the expected neutrino signal.

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arXiv2006

Simulation of Coherent Non-Linear Neutrino Flavor Transformation in the Supernova Environment I: Correlated Neutrino Trajectories

We present results of large-scale numerical simulations of the evolution of neutrino and antineutrino flavors in the region above the late-time post-supernova-explosion proto-neutron star. Our calculations are the first to allow explicit flavor evolution histories on different neutrino trajectories and to self-consistently couple flavor development on these trajectories through forward scattering-induced quantum entanglement. Employing the atmospheric-scale neutrino mass-squared difference and values of theta_13 allowed by current bounds, we find transformation of neutrino and antineutrino flavors over broad ranges of energy and luminosity in roughly the ``bi-polar'' collective mode. We find that this large-scale flavor conversion, largely driven by the flavor off-diagonal neutrino-neutrino forward scattering potential, sets in much closer to the proto-neutron star than simple estimates based on flavor-diagonal potentials and Mikeheyev-Smirnov-Wolfenstein evolution would indicate. In turn, this suggests that models of r-process nucleosynthesis sited in the neutrino-driven wind could be affected substantially by active-active neutrino flavor mixing, even with the small measured neutrino mass-squared differences.

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arXiv2006

Light Element Signatures of Sterile Neutrinos and Cosmological Lepton Numbers

We study primordial nucleosynthesis abundance yields for assumed ranges of cosmological lepton numbers, sterile neutrino mass-squared differences and active-sterile vacuum mixing angles. We fix the baryon-to-photon ratio at the value derived from the cosmic microwave background (CMB) data and then calculate the deviation of the 2H, 4He, and 7Li abundance yields from those expected in the zero lepton number(s), no-new-neutrino-physics case. We conclude that high precision (< 5% error) measurements of the primordial 2H abundance from, e.g., QSO absorption line observations coupled with high precision (< 1% error) baryon density measurements from the CMB could have the power to either: (1) reveal or rule out the existence of a light sterile neutrino if the sign of the cosmological lepton number is known; or (2) place strong constraints on lepton numbers, sterile neutrino mixing properties and resonance sweep physics. Similar conclusions would hold if the primordial 4He abundance could be determined to better than 10%.

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arXiv2006

Coherent Active-Sterile Neutrino Flavor Transformation in the Early Universe

We solve the problem of coherent Mikheyev-Smirnov-Wolfenstein (MSW) resonant active-to-sterile neutrino flavor conversion driven by an initial lepton number in the early universe. We find incomplete destruction of lepton number in this process and a sterile neutrino energy distribution with a distinctive cusp and high energy tail. These features imply alteration of the non-zero lepton number primordial nucleosynthesis paradigm when there exist sterile neutrinos with rest masses ~ 1 eV. This could result in better light element probes of (constraints on) these particles.

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arXiv2006

Bulk Viscosity, Decaying Dark Matter, and the Cosmic Acceleration

We discuss a cosmology in which cold dark-matter particles decay into relativistic particles. We argue that such decays could lead naturally to a bulk viscosity in the cosmic fluid. For decay lifetimes comparable to the present hubble age, this bulk viscosity enters the cosmic energy equation as an effective negative pressure. We investigate whether this negative pressure is of sufficient magnitude to account fo the observed cosmic acceleration. We show that a single decaying species in a flat, dark-matter dominated cosmology without a cosmological constant cannot reproduce the observed magnitude-redshift relation from Type Ia supernovae. However, a delayed bulk viscosity, possibly due to a cascade of decaying particles may be able to account for a significant fraction of the apparent cosmic acceleration. Possible candidate nonrelativistic particles for this scenario include sterile neutrinos or gauge-mediated decaying supersymmetric particles.

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arXiv2006

Dark matter sterile neutrinos in stellar collapse: alteration of energy/lepton number transport and a mechanism for supernova explosion enhancement

We investigate matter-enhanced Mikheyev-Smirnov-Wolfenstein (MSW) active-sterile neutrino conversion in the $ν_e \rightleftharpoons ν_s$ channel in the collapse of the iron core of a pre-supernova star. For values of sterile neutrino rest mass $m_s$ and vacuum mixing angle $θ$ (specifically, $0.5 {\rm keV}< m_s<10 {\rm keV}$ and $\sin^22θ> 5\times{10}^{-12}$) which include those required for viable sterile neutrino dark matter, our one-zone in-fall phase collapse calculations show a significant reduction in core lepton fraction. This would result in a smaller homologous core and therefore a smaller initial shock energy, disfavoring successful shock re-heating and the prospects for an explosion. However, these calculations also suggest that the MSW resonance energy can exhibit a minimum located between the center and surface of the core. In turn, this suggests a post-core-bounce mechanism to enhance neutrino transport and neutrino luminosities at the core surface and thereby augment shock re-heating: (1) scattering-induced or coherent MSW $ν_e\toν_s$ conversion occurs deep in the core, at the first MSW resonance, where $ν_e$ energies are large ($\sim 150$ MeV); (2) the high energy $ν_s$ stream outward at near light speed; (3) they deposit their energy when they encounter the second MSW resonance $ν_s\toν_e$ just below the proto-neutron star surface.

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arXiv2006

Neutrino-Accelerated Hot Hydrogen Burning

We examine the effects of significant electron anti-neutrino fluxes on hydrogen burning. Specifically, we find that the bottleneck weak nuclear reactions in the traditional pp-chain and the hot CNO cycle can be accelerated by anti-neutrino capture, increasing the energy generation rate. We also discuss how anti-neutrino capture reactions can alter the conditions for break out into the rp-process. We speculate on the impact of these considerations for the evolution and dynamics of collapsing very- and super- massive compact objects.

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arXiv2005

Flavor Changing Supersymmetry Interactions in a Supernova

We consider for the first time R-parity violating interactions of the Minimal Standard Supersymmetric Model involving neutrinos and quarks (``flavor changing neutral currents'', FCNC's) in the infall stage of stellar collapse. Our considerations extend to other kinds of flavor changing neutrino reactions as well. We examine non-forward neutrino scattering processes on heavy nuclei and free nucleons in the supernova core. This investigation has led to four principal original discoveries/products: (1) first calculation of neutrino flavor changing cross sections for spin one half (e.g. free nucleon) and spin zero nuclear targets; (2) discovery of nuclear mass number squared (A squared) coherent amplification of neutrino-quark FCNC's; (3) analysis of FCNC-induced alteration of electron capture and weak/nuclear equilibrium in the collapsing core; and (4) generalization of the calculated cross sections (mentioned in 1) for the case of hot heavy nuclei to be used in collapse/supernova and neutrino transport simulations. The scattering processes that we consider allow electron neutrinos to change flavor during core collapse, thereby opening holes in the electron neutrino sea, which allows electron capture to proceed and results in a lower core electron fraction. A lower electron fraction implies a lower homologous core mass, a lower shock energy, and a greater nuclear photo-disintegration burden for the shock. In addition, unlike the standard supernova model, the core now could have net muon and/or tau lepton numbers. These effects could be significant even for supersymmetric couplings below current experimental bounds.

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arXiv2005

Cosmological Lepton Asymmetry, Primordial Nucleosynthesis, and Sterile Neutrinos

We study post weak decoupling coherent active-sterile and active-active matter-enhanced neutrino flavor transformation in the early universe. We show that flavor conversion efficiency at Mikheyev-Smirnov-Wolfenstein resonances is likely to be high (adiabatic evolution) for relevant neutrino parameters and energies. However, we point out that these resonances cannot sweep smoothly and continuously with the expansion of the universe. We show how neutrino flavor conversion in this way can leave both the active and sterile neutrinos with non-thermal energy spectra, and how, in turn, these distorted energy spectra can affect the neutron-to-proton ratio, primordial nucleosynthesis, and cosmological mass/closure constraints on sterile neutrinos. We demonstrate that the existence of a light sterile neutrino which mixes with active neutrinos can change fundamentally the relationship between the cosmological lepton numbers and the primordial nucleosynthesis He-4 yield.

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arXiv2005

Simultaneous Flavor Transformation of Neutrinos and Antineutrinos with Dominant Potentials from Neutrino-Neutrino Forward Scattering

In astrophysical environments with intense neutrino fluxes, neutrino-neutrino forward scattering contributes both diagonal and off-diagonal potentials to the flavor-basis Hamiltonian that governs neutrino flavor evolution. We examine a special case where adiabatic flavor evolution can produce an off-diagonal potential from neutrino-neutrino forward scattering that dominates over both the corresponding diagonal term and the potential from neutrino-matter forward scattering. In this case, we find a solution that, unlike the ordinary Mikeyhev-Smirnov-Wolfenstein scenario, has both neutrinos and antineutrinos maximally mixed in medium over appreciable ranges of neutrino and antineutrino energy. Employing the measured solar and atmospheric neutrino mass-squared differences, we identify the conditions on neutrino fluxes that are required for this solution to exist deep in the supernova environment, where it could affect the neutrino signal, heavy-element nucleosynthesis, and even the revival of the supernova shock. We speculate on how this solution might or might not be attained in realistic supernova evolution. Though this solution is ephemeral in time and/or space in supernovae, it may signal the onset of subsequent appreciable flavor mixing for both neutrinos and antineutrinos. A similar solution may also exist in an early universe with significant net neutrino-lepton numbers.

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arXiv2004

APS Neutrino Study: Report of the Neutrino Astrophysics and Cosmology Working Group

In 2002, Ray Davis and Masatoshi Koshiba were awarded the Nobel Prize in Physics ``for pioneering contributions to astrophysics, in particular for the detection of cosmic neutrinos.'' However, while astronomy has undergone a revolution in understanding by synthesizing data taken at many wavelengths, the universe has only barely been glimpsed in neutrinos, just the Sun and the nearby SN 1987A. An entire universe awaits, and since neutrinos can probe astrophysical objects at densities, energies, and distances that are otherwise inaccessible, the results are expected to be particularly exciting. Similarly, the revolution in quantitative cosmology has heightened the need for very precise tests that depend on the effects of neutrinos, and prominent among them is the search for the effects of neutrino mass, since neutrinos are a small but known component of the dark matter. In this report, we highlight some of the key opportunties for progress in neutrino astrophysics and cosmology, and the implications for other areas of physics.

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arXiv2003

Pulsar kicks from a dark-matter sterile neutrino

We show that a sterile neutrino with mass in the 1-20 keV range and a small mixing with the electron neutrino can simultaneously explain the origin of the pulsar motions and the dark matter in the universe. An asymmetric neutrino emission from a hot nascent neutron star can be the explanation of the observed pulsar velocities. In addition to the pulsar kick mechanism based on resonant neutrino transitions, we point out a new possibility: an asymmetric off-resonant emission of sterile neutrinos. The two cases correspond to different values of the masses and mixing angles. In both cases we identify the ranges of parameters consistent with the pulsar kick, as well as cosmological constraints.

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arXiv2003

Cosmological Constraints on Bulk Neutrinos

Recent models invoking extra spacelike dimensions inhabited by (bulk) neutrinos are shown to have significant cosmological effects if the size of the largest extra dimension is R > 1 fm. We consider effects on cosmic microwave background anisotropies, big bang nucleosynthesis, deuterium and Li-6 photoproduction, diffuse photon backgrounds, and structure formation. The resulting constraints can be stronger than either bulk graviton overproduction constraints or laboratory constraints.

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arXiv2002

Estimates of Stellar Weak Interaction Rates for Nuclei in the Mass Range A=65-80

We estimate lepton capture and emission rates, as well as neutrino energy loss rates, for nuclei in the mass range A=65-80. These rates are calculated on a temperature/density grid appropriate for a wide range of astrophysical applications including simulations of late time stellar evolution and x-ray bursts. The basic inputs in our single particle and empirically inspired model are i) experimentally measured level and weak decay information, ii) estimates of matrix elements for allowed experimentally-unmeasured transitions based on the systematics of experimentally observed allowed transitions, and iii) estimates of the centroids of the GT resonances motivated by shell model calculations in the fp shell as well as by (n,p) and (p,n) experiments. Transitions involving Fermi resonances (isobaric analog states) are also included and dominate the rates for many interesting proton rich nuclei for which an experimentally-determined ground state lifetime is unavailable. To compare our results with more detailed shell model based calculations we also calculate weak rates for nuclei in the mass range A=60-65 for which Langanke and Martinez-Pinedo have provided rates. The typical deviation in the electron capture and B- decay rates for these ~30 nuclei is less than a factor of two or three for a wide range of temperature and density appropriate for pre-supernova stellar evolution. We also discuss some subtleties associated with the partition functions used in calculations of stellar weak rates and show that the proper treatment of the partition functions is essential for estimating high temperature beta decay rates. Partition functions based on un-converged Lanczos calculations can result in estimates of high temperature beta decay rates that are systematically low.

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