Chad T. Kishimoto

Lepton-number-driven sterile neutrino production in the early universe

We examine medium-enhanced, neutrino scattering-induced decoherent production of dark matter candidate sterile neutrinos in the early universe. In cases with a significant net lepton number we find two resonances, where the effective in-medium mixing angles are large. We calculate the lepton number depletion-driven evolution of these resonances. We describe the dependence of this evolution on lepton numbers, sterile neutrino rest mass, and the active-sterile vacuum mixing angle. We find that this resonance evolution can result in relic sterile neutrino energy spectra with a generic form which is sharply peaked in energy. We compare our complete quantum kinetic equation treatment with the widely-used quantum Zeno ansatz.

Coherent Active-Sterile Neutrino Flavor Transformation in the Early Universe

We solve the problem of coherent Mikheyev-Smirnov-Wolfenstein resonant active-to-sterile neutrino flavor conversion driven by an initial lepton number in the early Universe. We find incomplete destruction of the 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 nonzero lepton number primordial nucleosynthesis paradigm when there exist sterile neutrinos with rest masses m(s) approximately 1 eV. This could result in better light element probes of (constraints on) these particles.

Light Element Signatures of Sterile Neutrinos and Cosmological Lepton Numbers

Author(s): Smith, CJ; Fuller, GM; Kishimoto, CT; Abazajian, KN | Abstract: 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 H2, He4, and Li7 abundance yields from those expected in the zero-lepton number(s), no-new-neutrino-physics case. We conclude that high precision (l5% error) measurements of the primordial H2 abundance from, e.g., QSO absorption line observations coupled with high precision (l1% error) baryon density measurements from the CMB could have the power to either: (i) reveal or rule out the existence of a light sterile neutrino if the sign of the cosmological lepton number is known; or (ii) place strong constraints on lepton numbers, sterile neutrino mixing properties and resonance sweep physics. Similar conclusions would hold if the primordial He4 abundance could be determined to better than 10%.

Quantum Coherence of Relic Neutrinos

We argue that in at least a portion of the history of the Universe the relic background neutrinos are spatially extended, coherent superpositions of mass states. We show that an appropriate quantum mechanical treatment affects the neutrino mass values derived from cosmological data. The coherence scale of these neutrino flavor wave packets can be an appreciable fraction of the causal horizon size, raising the possibility of spacetime curvature-induced decoherence.

Probing neutrino physics with a self-consistent treatment of the weak decoupling, nucleosynthesis, and photon decoupling epochs

We show that a self-consistent and coupled treatment of the weak decoupling, big bang nucleosynthesis, and photon decoupling epochs can be used to provide new insights and constraints on neutrino sector physics from high-precision measurements of light element abundances and Cosmic Microwave Background observables. Implications of beyond-standard-model physics in cosmology, especially within the neutrino sector, are assessed by comparing predictions against five observables: the baryon energy density, helium abundance, deuterium abundance, effective number of neutrinos, and sum of the light neutrino mass eigenstates. We give examples for constraints on dark radiation, neutrino rest mass, lepton numbers, and scenarios for light and heavy sterile neutrinos.

Lepton asymmetry, neutrino spectral distortions, and big bang nucleosynthesis

PHYSICAL REVIEW D 95, 063503 (2017) Lepton asymmetry, neutrino spectral distortions, and big bang nucleosynthesis E. Grohs, 1 George M. Fuller, 2 C. T. Kishimoto, 2,3 and Mark W. Paris 4 Department of Physics, University of Michigan, Ann Arbor, Michigan 48109, USA Department of Physics, University of California, San Diego, La Jolla, California 92093, USA Department of Physics and Biophysics, University of San Diego, San Diego, California 92110, USA Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA (Received 9 December 2016; published 3 March 2017) We calculate Boltzmann neutrino energy transport with self-consistently coupled nuclear reactions through the weak-decoupling-nucleosynthesis epoch in an early universe with significant lepton numbers. We find that the presence of lepton asymmetry enhances processes which give rise to nonthermal neutrino spectral distortions. Our results reveal how asymmetries in energy and entropy density uniquely evolve for different transport processes and neutrino flavors. The enhanced distortions in the neutrino spectra alter the expected big bang nucleosynthesis light element abundance yields relative to those in the standard Fermi-Dirac neutrino distribution cases. These yields, sensitive to the shapes of the neutrino energy spectra, are also sensitive to the phasing of the growth of distortions and entropy flow with time/scale factor. We analyze these issues and speculate on new sensitivity limits of deuterium and helium to lepton number. DOI: 10.1103/PhysRevD.95.063503 I. INTRODUCTION In this paper we use the BURST neutrino-transport code [1] to calculate the baseline effects of out-of-equilibrium neutrino scattering on nucleosynthesis in an early universe with a nonzero lepton number, i.e., an asymmetry in the numbers of neutrinos and antineutrinos. Our baseline includes a strong, electromagnetic, and weak nuclear reaction network; modifications to the equation of state for the primeval plasma; and a Boltzmann neutrino energy transport network. We do not include neutrino flavor oscillations in this work. Our intent is to provide a coupled Boltzmann transport and nuclear reaction calculation to which future oscillation calculations can be compared. In fact, the outstanding issues in achieving ultimate precision in big bang nucleosynthesis (BBN) simulations will revolve around oscillations and plasma physics effects. These issues exist in both the zero and nonzero lepton-number cases, but are more acute in the presence of an asymmetry. We self-consistently follow the evolution of the neutrino phase-space occupation numbers through the weak- decoupling-nucleosynthesis epoch. There are many studies of the effects of lepton numbers on light element, BBN abundance yields. Early work [2,3] briefly explored the changes in the helium-4 ( 4 He) abundance in the presence of large neutrino degeneracies. Later work considered how lepton numbers could influence the 4 He yield [4,5] through neutrino oscillations. In addition, other works employed lepton numbers to constrain the cosmic microwave back- ground (CMB) radiation energy density [6,7] or the sum of the light neutrino masses [8]. References [9,10] simulta- neously investigated BBN abundances and CMB quantities using lepton numbers. The most recent work has used the primordial abundances to constrain lepton numbers which have been invoked to produce sterile neutrinos through matter-enhanced Mikheyev-Smirnow-Wolfenstein reso- nances [11–13]. Currently, our best constraints on these lepton numbers come from comparing the observationally inferred primordial abundances of either 4 He or deuterium (D) with the predicted yields of 4 He and D calculated in these models. Previous BBN calculations with neutrino asymmetry have made the assumption that the neutrino energy dis- tribution functions have thermal, Fermi-Dirac (FD) shaped forms. In fact, we know that neutrino scattering with electrons, positrons, and other neutrinos and electron- positron annihilation produce nonthermal distortions in these energy distributions, with concomitant effects on BBN abundance yields [1]. Though the nucleosynthesis changes induced with self-consistent transport are small, they nevertheless may be important in the context of high precision cosmology. Anticipated Stage-IV CMB measure- ments [14,15] of primordial helium and the relativistic energy density fraction at photon decoupling, coupled with the expected high precision deuterium measurements made with future 30-m class telescopes [16–20] will provide new probes of the relic neutrino history. In the standard cosmology with zero lepton numbers, neutrino oscillations act to interchange the populations of electron neutrinos and antineutrinos (ν e , ν ¯ e ) with those of muon and tau species (ν μ , ν ¯ μ , ν τ , ν ¯ τ ) [21]. Once we posit that there are asymmetries in the numbers of neutrinos and antineutrinos in one or more neutrino flavors, then neutrino

An optimization-based approach to calculating neutrino flavor evolution

Author(s): Armstrong, Eve; Patwardhan, Amol V; Johns, Lucas; Kishimoto, Chad T; Abarbanel, Henry DI; Fuller, George M

Effect of neutrino rest mass on ionization equilibrium freeze-out

Author(s): Grohs, E; Fuller, GM; Kishimoto, CT; Paris, MW | Abstract:

Neutrino-Accelerated Hot Hydrogen Burning

We examine the effects of significant electron antineutrino fluxes on hydrogen burning. Specifically, we find that the bottleneck weak nuclear reactions in the traditional p-p chain and the hot CNO cycle can be accelerated by antineutrino capture, increasing the energy generation rate. We also discuss how antineutrino 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 massive and supermassive compact objects.

Neutrino-Induced Hydrogen Burning

The principal hydrogen burning mechanisms that take place in stars have been elucidated and explored for many decades. However, the introduction of a prodigious flux of electron anti‐neutrinos would significantly accelerate these mechanisms and change the path toward the production of an α particle. We discuss the nature of such changes in the hydrogen burning mechanisms, and the side effects spawned from such alterations.