arXiv subjects

Daniel Boyanovsky

Publications and source records attributed to Daniel Boyanovsky.

At least 37 records · Page 2Linked to original sources

arXiv2020

On the origin of entropy of gravitationally produced dark matter: the entanglement entropy

We study the emergence of entropy in gravitational production of dark matter particles, ultra light scalars minimally coupled to gravity and heavier fermions, from inflation to radiation domination (RD). Initial conditions correspond to dark matter fields in their Bunch-Davies vacua during inflation. The "out" states are correlated particle-antiparticle pairs, and the distribution function is found in both cases. In the adiabatic regime the density matrix features rapid decoherence by dephasing from interference effects in the basis of "out" particle states, effectively reducing it to a diagonal form with a concomitant von Neumann entropy. We show that it is exactly the entanglement entropy obtained by tracing over one member of the correlated pairs. Remarkably, for both statistics the entanglement entropy is similar to the quantum kinetic entropy in terms of the distribution function with noteworthy differences stemming from pair correlations. The entropy and the kinetic fluid form of the energy momentum tensor all originate from decoherence of the density matrix. For ultra light scalar dark matter, the distribution function peaks at low momentum $\propto 1/k^3$ and the specific entropy is $\ll 1$. This is a hallmark of a \emph{condensed phase} but with vanishing field expectation value. For fermionic dark matter the distribution function is nearly thermal and the specific entropy is $\mathcal{O}(1)$ typical of a thermal species. We argue that the functional form of the entanglement entropy is quite general and applies to alternative production mechanisms such as parametric amplification during reheating.

gr-qc↗

arXiv2020

Gravitational production of nearly thermal fermionic Dark Matter

We consider the cosmological production of fermionic dark matter during inflation and a post-inflationary radiation dominated era. This fermion \emph{only interacts gravitationally}, has a mass $m$ much smaller than the Hubble scale during inflation (but is otherwise arbitrary) and is in its Bunch-Davies vacuum state during inflation. We focus on superhorizon modes at the end of inflation, and assume instantaneous reheating. We obtain the full energy momentum tensor discussing its renormalization, and show that the contribution from particle production is of the kinetic-fluid form near matter-radiation equality. We find \emph{exactly} the distribution function of produced particles $|B(k)|^2=\frac{1}{2}\Big[1-(1-e^{-\frac{k^2}{2mT_H}})^{1/2}\Big]$ which exhibits an " emergent temperature" $T_H=H_0\sqrt{Ω_R}\simeq 10^{-36}(\mathrm{eV})$. The abundance of the produced particles $Ω_{pp}$ is very similar to that of a non-relativistic degree of freedom thermalized at temperature $T_H$, $Ω_{pp} \propto m \, (m\,T_H)^{3/2}\simeq \big(m/10^8\mathrm{GeV})\big)^{5/2}$ and "cold" equation of state $w(a) \simeq (T_H/m a^2)$, both dominated by superhorizon modes at the end of inflation. We discuss subtle aspects of isocurvature perturbations.

astro-ph.CO↗

arXiv2020

Non-adiabatic cosmological production of ultra-light Dark Matter

We study the non-adiabatic cosmological production of ultra light dark matter (ULDM) under a minimal set of assumptions: a free ultra light real scalar as a spectator field in its Bunch-Davies vacuum state during inflation and instantaneous reheating into a radiation dominated era. For (ULDM) fields minimally coupled to gravity, non-adiabatic particle production yields a \emph{distribution function} peaked at \emph{low} comoving momentum $\mathcal{N}_k \propto 1/k^3$. The infrared behavior is a remnant of the infrared enhancement of light minimally coupled fields during inflation. We obtain the full energy momentum tensor, show explicity its equivalence with the fluid-kinetic one in the adiabatic regime, and extract the abundance, equation of state and free streaming length (cutoff in the matter power spectrum). Taking the upper bound on the scale of inflation from Planck, the (UDLM) saturates the dark matter abundance for $m \simeq 1.5\,\times 10^{-5}\mathrm{eV}$ with an equation of state parameter $w \simeq 10^{-14}$ and a free streaming length $λ_{fs} \simeq 70\,\mathrm{pc}$. Thus this cosmologically produced (ULDM) yields a \emph{cold} dark matter particle. We argue that the abundance from non-adiabatic production yields a \emph{lower bound} on generic (ULDM) and axion-like particles that must be included in any assessment of (ULDM) as a dark matter candidate.

gr-qc↗

arXiv2019

Dynamics of relaxation and dressing of a quenched Bose polaron

We study the non-equilibrium dynamics of relaxation and dressing of a mobile impurity suddenly immersed--or quenched-- into a zero temperature homogeneous Bose Einstein condensate (BEC) with velocity $v$. A many body generalization of Weisskopf-Wigner theory is implemented to obtain the impurity fidelity, reduced density matrix and entanglement entropy. The dynamics depend crucially on the Mach number $β=v/c$, with $c$ the speed of sound of superfluid phonons and features many different time scales. Quantum Zeno behavior at early time is followed by relaxational and dressing dynamics determined by Cerenkov emission of long-wavelength phonons for $β>1$ with a decay rate $Γ_p \propto (β-1)^3$. The polaron dressing dynamics \emph{slows-down} as $β\rightarrow 1$ and is characterized by power laws $t^{-α}$ with different exponents for $β\lessgtr 1$. The asymptotic entanglement entropy features a sharp discontinuity and the residue features a cusp at $β=1$. These non-equilibrium features suggest \emph{universal} dynamical critical phenomena near $β\simeq 1$, and are a direct consequence of the linear dispersion relation of long wavelength superfluid phonons. We conjecture on the emergence of an asymptotic dynamical attractor with $β\leq 1$.

cond-mat.quant-gas↗

arXiv2019

Cosmological decay of Higgs-like scalars into a fermion channel

We study the decay of a Higgs-like scalar Yukawa coupled to massless fermions in post-inflationary cosmology, combining a non-perturbative method with an adiabatic expansion. The renormalized survival probability $\mathcal{P}_Φ(t)$ of a (quasi) particle ``born'' at time $t_b$ and decaying at rest in the comoving frame, $\mathcal{P}_Φ(t) = \Big[\frac{t}{t_b}\Big]^{-\frac{Y^2}{8π^2}}~ e^{ \frac{Y^2}{4π^2}\,\big(t/t_b\big)^{1/4} } \,e^{-Γ_0\,(t-t_b)}~ \mathcal{P}_Φ(t_b) $, with $Γ_0$ the decay rate at rest in Minkowski space-time. For an ultrarelativistic particle we find $\mathcal{P}_Φ(t) = e^{-\frac{2}{3}Γ_0\,t_{nr}\,(t/t_{nr})^{3/2}}~ \mathcal{P}_Φ(t_b)$ before it becomes non-relativistic at a time $t_{nr}$ as a consequence of the cosmological redshift. For $t\gg t_{nr}$ we find $\mathcal{P}_Φ(t) = \Big[\frac{t}{t_{nr}}\Big]^{-\frac{Y^2}{8π^2}}~ e^{ \frac{Y^2}{4π^2}\,\big(t/t_{nr}\big)^{1/4} }~\Big[\frac{t}{t_{nr}}\Big]^{Γ_0 t_{nr}/2} \,e^{-Γ_0\,(t-t_{nr})}~ \mathcal{P}_Φ(t_{nr})$. The extra power is a consequence of the memory on the past history of the decay process. We compare these results to an S-matrix inspired phenomenological Minkowski-like decay law modified by an instantaneous Lorentz factor to account for cosmological redshift. Such phenomenological description \emph{under estimates the lifetime of the particle}. For very long lived, very weakly coupled particles, we obtain an \emph{upper bound} for the survival probability as a function of redshift $z$ valid throughout the expansion history $\mathcal{P}_Φ(z) \gtrsim e^{-\frac{Γ_0}{H_0}\,Υ(z,z_b)}\,\mathcal{P}_Φ(z_b)$, where $Υ(z,z_b)$ only depends on cosmological parameters and $t_{nr}$.

hep-ph↗

arXiv2019

Quantum decay in renormalizable field theories: quasiparticle formation, Zeno and anti-Zeno effects

In a renormalizable theory the survival probability of an unstable quantum state features divergences as a consequence of the rapid growth of the density of states with energy. Introducing a high energy cutoff $Λ$, the transient dynamics during a time scale $\simeq 1/Λ$ describes the renormalization of the bare into a `quasiparticle' state which decays on longer time scales. During this early transient the decay law features Zeno behavior $e^{-(t/t_Z)^2}$ with the Zeno time-scale $t_Z \propto 1/Λ^{3/2}$. We introduce a dynamical renormalization framework that allows to separate consistently the dynamics of formation of the quasiparticle state and its decay on longer time scales by introducing a renormalization time scale along with alternative `schemes'. The survival probability obeys a renormalization group equation with respect to this scale. We find a transient \emph{suppression} of the decay law for large Lorentz factor as a consequence of the narrowing of the phase space for decay different from the usual time dilation. In presence of higher mass thresholds, the energy uncertainty associated with transient dynamics leads to an \emph{anti Zeno enhancement} with a transient acceleration of the decay into \emph{heavier particles}. There remains memory of the transient effects in the survival probability even at long time. We discuss possible consequences of these effects in cosmology.

hep-th↗

arXiv2018

Particle decay in post inflationary cosmology

We study scalar particle decay during the radiation and matter dominated epochs of a standard cosmological model. An adiabatic approximation is introduced that is valid for degrees of freedom with typical wavelengths much smaller than the particle horizon ($\propto$~Hubble radius) at a given time. We implement a non-perturbative method that includes the cosmological expansion and obtain a cosmological Fermi's Golden Rule that enables one to compute the decay law of a parent particle of mass $m_1$, along with the build up of the population of daughter particles of mass $m_2$. The survival probability of the decaying particle is $P(t)=e^{-\widetildeΓ_k(t)\,t}$ with $\widetildeΓ_k(t)$ being an \emph{effective momentum and time dependent decay rate}. It features a transition time scale $t_{nr}$ between the relativistic and non-relativistic regimes and for $k \neq 0$ is always smaller than the analogous rate in Minkowski spacetime, as a consequence of (local) time dilation and the cosmological redshift. For $t \ll t_{nr}$ the decay law is a "stretched exponential" $P(t) = e^{-(t/t^*)^{3/2}}$, whereas for the non-relativistic stage with $t \gg t_{nr}$, we find $P(t) = e^{-Γ_0 t}\,(t/t_{nr})^{Γ_0\,t_{nr}/2}$. The Hubble time scale $\propto 1/H(t)$ introduces an energy uncertainty $ΔE \sim H(t)$ which relaxes the constraints of kinematic thresholds. This opens new decay channels into heavier particles for $2πE_k(t) H(t) \gg 4m^2_2-m^2_1$, with $E_k(t)$ the (local) comoving energy of the decaying particle. As the expansion proceeds this channel closes and the usual two particle thresholds restrict the decay kinematics.

hep-ph↗

arXiv2018

Imprint of entanglement entropy in the power spectrum of inflationary fluctuations

If the inflaton couples to other degrees of freedom that populate the post-inflationary stage, such coupling modifies the dynamics of the inflaton \emph{during} inflation. We consider light fermions Yukawa coupled to the inflaton as "unobserved" degrees of freedom integrated out of the total density matrix. Tracing out these degrees of freedom yields a \emph{mixed} density matrix whose time evolution is described by an effective field theory. We show that the coupling leads to profuse fermion pair production for super-Hubble inflaton fluctuations which lead to the \emph{growth of entanglement entropy during inflation}. The power spectrum of inflaton fluctuations features scale invariance violations $\mathcal{P}(k) = \mathcal{P}_0(k)\,\,\exp\{8\,ξ_k\}$ with corrections to the \emph{index and its running directly correlated with the entanglement entropy}: $S_{vN} = - \sum_{k} \Big[ \ln(1-ξ_k) + \frac{ξ_k\,\ln(ξ_k)}{1-ξ_k} \Big]$. For super-Hubble fluctuations we find $ξ_k = -\frac{Y^2}{48π^2}\Big\{2\,N_T\,\ln(k/k_f) + \ln^2(k/k_f)\Big\}$ with $Y$ the Yukawa coupling, $N_T$ the total number of e-folds during inflation, and $k_f$ a "pivot" scale corresponding to the mode that crosses the Hubble radius at the end of inflation.

astro-ph.CO↗

arXiv2018

Information loss in effective field theory: entanglement and thermal entropies

Integrating out high energy degrees of freedom to yield a low energy effective field theory leads to a loss of information with a concomitant increase in entropy. We obtain the effective field theory of a light scalar field interacting with heavy fields after tracing out the heavy degrees of freedom from the time evolved density matrix. The initial density matrix describes the light field in its ground state and the heavy fields in equilibrium at a common temperature $T$. For $T=0$, we obtain the reduced density matrix in a perturbative expansion, it reveals an emergent mixed state as a consequence of the entanglement between light and heavy fields. We obtain the effective action that determines the time evolution of the \emph{reduced} density matrix for the light field in a non-perturbative Dyson resummation of one-loop correlations of the heavy fields. The Von-Neumann \emph{entanglement entropy} associated with the reduced density matrix is obtained for the non-resonant and resonant cases in the asymptotic long time limit. In the non-resonant case the reduced density matrix displays an \emph{incipient} thermalization albeit with a wave-vector, time and coupling dependent \emph{effective temperature} as a consequence of memory of initial conditions. The entanglement entropy is time independent and is the \emph{thermal entropy} for this effective, non-equilibrium temperature. In the resonant case the light field fully \emph{thermalizes} with the heavy fields, the reduced density matrix looses memory of the initial conditions and the entanglement entropy becomes the \emph{thermal entropy} of the light field. We discuss the relation between the entanglement entropy ultraviolet divergences and renormalization.

hep-th↗

arXiv2017

Heisenberg-Langevin vs. quantum master equation

The quantum master equation is an important tool in the study of quantum open systems. It is often derived under a set of approximations, chief among them the Born (factorization) and Markov (neglect of memory effects) approximations. In this article we study the paradigmatic model of quantum Brownian motion of an harmonic oscillator coupled to a bath of oscillators with a Drude-Ohmic spectral density. We obtain analytically the \emph{exact} solution of the Heisenberg-Langevin equations, with which we study correlation functions in the asymptotic stationary state. We compare the \emph{exact} correlation functions to those obtained in the asymptotic long time limit with the quantum master equation in the Born approximation \emph{with and without} the Markov approximation. In the latter case we implement a systematic derivative expansion that yields the \emph{exact} asymptotic limit under the factorization approximation \emph{only}. We find discrepancies that could be significant when the bandwidth of the bath $Λ$ is much larger than the typical scales of the system. We study the \emph{exact} interaction energy as a \emph{proxy} for the correlations missed by the Born approximation and find that its dependence on $Λ$ is similar to the \emph{discrepancy} between the exact solution and that of the quantum master equation in the Born approximation. We quantify the regime of validity of the quantum master equation in the Born approximation with or without the Markov approximation in terms of the system's relaxation rate $γ$, its \emph{unrenormalized} natural frequency $Ω$ and $Λ$: $γ/Ω\ll 1$ and \emph{also} $γΛ/Ω^2 \ll 1$. The reliability of the Born approximation is discussed within the context of recent experimental settings and more general environments.

quant-ph↗

arXiv2017

Kinetic mixing between a Higgs and a nearly degenerate Dark scalar: oscillations and displaced vertices

Extensions beyond the Standard Model allow for a gauge singlet scalar to be kinetically coupled with the Higgs. We consider kinetic mixing between a Dark scalar gauge singlet \emph{nearly degenerate} with the Higgs, focusing on the \emph{dynamical} aspects of the mixing phenomena. The renormalization program is carried out by obtaining the one-loop effective action which yields an effective non-hermitian Hamiltonian to study the dynamics of mixing. The scalar Higgs becomes a coherent superposition of the mass eigenstates, thus kinetic mixing leads to oscillations and common decay channels in striking similarity with neutral meson mixing. Near degeneracy yields an \emph{enhancement} of the kinetic coupling. For small kinetic mixing we find that the mass eigenstates feature different lifetimes which result in a wide separation of time scales of evolution along with important coherence aspects from Dark scalar-Higgs interference. The wide separation of scales is manifest as displaced decay vertices which could potentially be a telltale experimental signal of kinetic mixing.

hep-ph↗

arXiv2017

Coherence and entanglement of mechanical oscillators mediated by coupling to different baths

We study the non-equilibrium dynamics of two coupled mechanical oscillators with general linear couplings to two uncorrelated thermal baths at temperatures $T_1$ and $T_2$, respectively. We obtain the complete solution of the Heisenberg-Langevin equations, which reveal a coherent mixing among the normal modes of the oscillators as a consequence of their off-diagonal couplings to the baths. Unique renormalization aspects resulting from this mixing are discussed. Diagonal and off-diagonal (coherence) correlation functions are obtained analytically in the case of strictly Ohmic baths with different couplings in the strong and weak coupling regimes. An asymptotic non-equilibrium stationary state emerges for which we obtain the complete expressions for the correlations and coherence. Remarkably the coherence survives in the high temperature, classical limit for $T_1 \neq T_2$. In the case of vanishing detuning between the oscillator normal modes both coupling to one and the same bath the coherence retains memory of the initial conditions at long time. A perturbative expansion of the early time evolution reveals that the emergence of coherence is a consequence of the entanglement between the normal modes of the oscillators \emph{mediated} by their couplings to the baths. This \emph{suggests} the survival of entanglement in the high temperature limit for different temperatures of the baths which is essentially a consequence of the non-equilibrium nature of the asymptotic stationary state. An out of equilibrium setup with small detuning and large $|T_1- T_2|$ produces non-vanishing steady-state coherence and entanglement in the high temperature limit of the baths.

quant-ph↗

arXiv2017

Production of heavy sterile neutrinos from vector boson decay at electroweak temperatures

In the standard model extended with a seesaw mass matrix, we study the production of sterile neutrinos from the decay of vector bosons at $T\simeq M_{W,Z}$. We derive a general quantum kinetic equation for the production of sterile neutrinos and their effective mixing angles valid in a wide range of temperature, to all orders in interactions of the standard model, and to leading order mixing angle $θ\ll 1$. Production rates and effective mixing angles depend sensitively on helicity. Positive helicity states interact more weakly with the medium and their effective mixing angle is not modified significantly whereas the mixing angle for negative helicity is strongly suppressed by the medium. If $M_s \lesssim 8.35\,\mathrm{MeV}$, there are fewer states with negative helicity produced than those with positive helicity. There is an MSW resonance in the absence of lepton asymmetry, but is screened by the damping rate, without production enhancement. Negative helicity states freeze-out at $T^-_f\simeq 5\,\mathrm{GeV}$ and positive helicity states freeze-out at $T^+_f \simeq 8\,\mathrm{GeV}$, both distributions are far from thermal. Negative helicity states feature a broader momentum distribution than that for those with positive helicity. Sterile neutrinos produced via vector boson decay do not satisfy the abundance, lifetime and cosmological constraints to be the sole dark matter component in the universe but might solve the $^{7}Li$ problem, albeit at the very edge of the possible parameter space. A heavy sterile neutrino with a mass of a few MeV could decay into light sterile neutrinos, of a few keV in mass, that contribute to warm dark matter. We argue that heavy sterile neutrinos with lifetime $\leq 1/H_0$ reach local thermodynamic equilibrium.

hep-ph↗

arXiv2016

The case for mixed dark matter from sterile neutrinos

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. The same weak interaction processes that produce active-like neutrinos also produce the heavier species. We introduce the 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. We identify processes in which finite temperature collective excitations lead to the production of the heavy species. As a specific example, we consider the production of heavy neutrinos 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 \emph{conjecture} that those with lifetimes $τ\ll 1/H_0$ may undergo cascade decay into lighter DM candidates and/or inject non-LTE neutrinos into the cosmic neutrino background. We provide a comparison with non-resonant production via active-sterile mixing.

astro-ph.CO↗

arXiv2016

Fermionic influence (action) on inflationary fluctuations

Motivated by apparent persistent large scale anomalies in the CMB we study the influence of fermionic degrees of freedom on the dynamics of inflaton fluctuations as a possible source of violations of (nearly) scale invariance on cosmological scales. We obtain the non-equilibrium effective action of an inflaton-like scalar field with Yukawa interactions ($Y_{D,M}$) to light \emph{fermionic} degrees of freedom both for Dirac and Majorana fields in de Sitter space-time. The effective action leads to Langevin equations of motion for the fluctuations of the inflaton-like field, with self-energy corrections and a stochastic gaussian noise. We solve the Langevin equation in the super-Hubble limit implementing a dynamical renormalization group resummation. For a nearly massless inflaton its power spectrum of super Hubble fluctuations is \emph{enhanced}, $\mathcal{P}(k;η) = (\frac{H}{2π})^2\,e^{γ_t[-kη] }$ with $γ_t[-kη] = \frac{1}{6π^2} \Big[\sum_{i=1}^{N_D}{Y^2_{i,D}}+2\sum_{j=1}^{N_M}{Y^2_{j,M}}\Big]\,\Big\{\ln^2[-kη]-2 \ln[-kη]\ln[ -kη_0] \Big\} $ for $N_D$ Dirac and $N_M$ Majorana fermions, and $η_0$ is the renormalization scale at which the inflaton mass vanishes. The full power spectrum is shown to be renormalization group invariant. These corrections to the super-Hubble power spectrum entail a violation of scale invariance as a consequence of the coupling to the fermionic fields. The effective action is argued to be \emph{exact} in a limit of large number of fermionic fields. A cancellation between the enhancement from fermionic degrees of freedom and suppression from light scalar degrees of freedom \emph{conformally coupled to gravity} suggests the possibility of a finely tuned \emph{supersymmetry} among these fields.

gr-qc↗

arXiv2015

Cosmological Implications of Light Sterile Neutrinos produced after the QCD Phase Transition

We study the production of sterile neutrinos in the early universe from $π\rightarrow l ν_s$ 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 $\lesssim 1 MeV$ produced via this mechanism freeze-out at $T_f \simeq 10 MeV$ with a distribution function that is highly non-thermal and features a sharp enhancement at low momentum thereby making this species \emph{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 $π\rightarrow μν_s$, the bounds lead to a narrow region of compatibility with the latest results from the $3.55 \mathrm{KeV}$ line. The non-thermal distribution function leads to free-streaming lengths (today) in the range of $\sim \mbox{few kpc}$ consistent with the observation of cores in dwarf galaxies. For sterile neutrinos with mass $\lesssim 1 eV$ 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 $N_{eff}$.

astro-ph.CO↗

arXiv2014

Nearly degenerate heavy sterile neutrinos in cascade decay: mixing and oscillations

Some extensions beyond the Standard Model propose the existence of nearly degenerate heavy sterile neutrinos. If kinematically allowed these can be resonantly produced and decay in a cascade to common final states. The common decay channels lead to mixing of the heavy sterile neutrino states and interference effects. We implement non-perturbative methods to study the dynamics of the cascade decay to common final states, which features similarities but also noteworthy differences with the case of neutral meson mixing. We show that mixing and oscillations among the nearly degenerate sterile neutrinos can be detected as \emph{quantum beats} in the distribution of final states produced from their decay. These oscillations would be a telltale signal of mixing between heavy sterile neutrinos. We study in detail the case of two nearly degenerate sterile neutrinos produced in the decay of pseudoscalar mesons and decaying into a purely leptonic "visible" channel: $ν_h \rightarrow e^+ e^- ν_a$. Possible cosmological implications for the effective number of neutrinos $N_{eff}$ are discussed.

hep-ph↗

arXiv2014

Space-time evolution of heavy sterile neutrinos in cascade decays

Heavy sterile-like neutrinos may be produced resonantly from the decay of pseudoscalar mesons and may decay into several different channels in a cascade $Φ\rightarrow L^αν_h;ν_h\rightarrow \{X\}$. In general these are rare events with displaced vertices. We provide a non-perturbative and manifestly unitary framework that describes the cascade decay and yields the space-time evolution of the probabilities for sterile neutrinos, final states and the total number of events at a far detector. The results are general, valid for Dirac or Majorana neutrinos and only input the total decay rates and branching ratios for the production and decay channels. We apply the general results to two examples of "visible" decay: i) $K^+\rightarrow e^+ ν_h\rightarrow (e^+) e^+ e^- ν_e$ via a standard model charged current vertex and ii) the radiative decay $K^+\rightarrow μ^+ ν_h \rightarrow (μ^+) ν_a γ$. For this latter cascade process we find substantial corrections to previous assessments within the parameter space argued to solve the anomalous excess of electron-like events at MiniBooNE. These large corrections may help relieve the tension with recent experimental bounds on radiative decays of heavy sterile neutrinos.

hep-ph↗