Nonequilibrium pion dynamics near the critical point in a constituent quark model

2015

Phys. Rev. D

We study the production of sterile neutrinos in the early universe from π → lν s shortly after the QCD phase transition in the absence of a lepton asymmetry while including finite temperature corrections to the π mass and decay constant f π . Sterile neutrinos with masses 1M eV produced via this mechanism freeze-out at T f ≃ 10M eV with a distribution function that is highly nonthermal and features a sharp enhancement at low momentum thereby making this species cold even for very light masses. Dark matter abundance constraints from the CMB and phase space density constraints from the most dark matter dominated dwarf spheroidal galaxies provide upper and lower bounds respectively on combinations of mass and mixing angles. For π → µν s , the bounds lead to a narrow region of compatibility with the latest results from the 3.55KeV line. The non-thermal distribution function leads to free-streaming lengths (today) in the range of ∼ few kpc consistent with the observation of cores in dwarf galaxies. For sterile neutrinos with mass 1eV that are produced by this reaction, the most recent accelerator and astrophysical bounds on U ls combined with the non-thermal distribution function suggests a substantial contribution from these sterile neutrinos to N ef f .

Section: Introductionmentioning

confidence: 99%

Cosmological implications of light sterile neutrinos produced after the QCD phase transition

Lello

2015

Phys. Rev. D

“…Instead, in this section, we study the production from pion decay by relying on the well understood effective field theory description of weak interactions of pions, enhanced by the results of a systematic program that studied finite temperature corrections to the pion decay constant and mass implementing non-perturbative techniques from chiral perturbation theory, linear and non-linear sigma models and lattice gauge theory [105][106][107][108][109][110][111][112][113][114][115][116][117][118][119][120]. There are at least three important reasons that motivate this study: (1) it is a clear and relevant example of the quantum kinetic equation approach to production and freeze out that includes consistently finite temperature corrections.…”

Section: Sterile Neutrinos From Pion Decaymentioning

confidence: 99%

Sterile Neutrinos as Dark Matter: Alternative Production Mechanisms in the Early Universe

2021

Universe

We study various production mechanisms of sterile neutrinos in the early universe beyond and within the standard model. We obtain the quantum kinetic equations for production and the distribution function of sterile-like neutrinos at freeze-out, from which we obtain free streaming lengths, equations of state and coarse grained phase space densities. In a simple extension beyond the standard model, in which neutrinos are Yukawa coupled to a Higgs-like scalar, we derive and solve the quantum kinetic equation for sterile production and analyze the freeze-out conditions and clustering properties of this dark matter constituent. We argue that in the mass basis, standard model processes that produce active neutrinos also yield sterile-like neutrinos, leading to various possible production channels. Hence, the final distribution function of sterile-like neutrinos is a result of the various kinematically allowed production processes in the early universe. As an explicit example, we consider production of light sterile neutrinos from pion decay after the QCD phase transition, obtaining the quantum kinetic equation and the distribution function at freeze-out. A sterile-like neutrino with a mass in the keV range produced by this process is a suitable warm dark matter candidate with a free-streaming length of the order of few kpc consistent with cores in dwarf galaxies.

“…Instead, in this section we study the production from pion decay by relying on the well understood effective field theory description of weak interactions of pions, enhanced by the results of a systematic program that studied finite temperature corrections to the pion decay constant and mass implementing non-perturbative techniques from chiral perturbation theory, linear and non-linear sigma models and lattice gauge theory [164][165][166][167][168][169][170][171][172][173][174][175][176][177][178][179][180][181]. There are at least three important reasons that motivate this study: 1) it is a clear and relevant example of the quantum kinetic equation approach to production and freeze out that includes consistently finite temperature corrections.…”

Section: Jcap06(2016)011mentioning

confidence: 99%

The case for mixed dark matter from sterile neutrinos

Lello

J. Cosmol. Astropart. Phys.

2016

Sterile neutrinos are SU (2) singlets that mix with active neutrinos via a mass matrix, its diagonalization leads to mass eigenstates that couple via standard model vertices. We study the cosmological production of heavy neutrinos via standard model charged and neutral current vertices under a minimal set of assumptions: i) the mass basis contains a hierarchy of heavy neutrinos, ii) these have very small mixing angles with the active (flavor) neutrinos, iii) standard model particles, including light (active-like) neutrinos are in thermal equilibrium. If kinematically allowed, the same weak interaction processes that produce active-like neutrinos also produce the heavier species. We introduce the quantum kinetic equations that describe their production, freeze out and decay and discuss the various processes that lead to their production in a wide range of temperatures assessing their feasibility as dark matter candidates. The final distribution function at freeze-out is a mixture of the result of the various production processes. We identify processes in which finite temperature collective excitations may lead to the production of the heavy species. As a specific example, we consider the production of heavy neutrinos in the mass range M h 140 MeV from pion decay shortly after the QCD crossover including finite temperature corrections to the pion form factors and mass. We consider the different decay channels that allow for the production of heavy neutrinos showing that their frozen distribution functions exhibit effects from "kinematic entanglement" and argue for their viability as mixed dark matter candidates. We discuss abundance, phase space density and stability constraints and argue that heavy neutrinos with lifetime τ > 1/H 0 freeze out of local thermal equilibrium, and conjecture that those with lifetimes τ ≪ 1/H 0 may undergo cascade decay into lighter DM candidates and/or inject non-LTE neutrinos into the cosmic neutrino background. A comparison is made between production through pion decays with the production of non-resonant production via active-sterile mixing.