We provide a semi-analytic study of the small scale aspects of the power spectra of warm dark matter (WDM) candidates that decoupled while relativistic with arbitrary distribution functions. These are characterized by two widely different scales k eq ∼ 0.01 (Mpc) −1 and k f s = √ 3 k eq /2 V 2 eq 1 2with V 2 eq 1 2 ≪ 1 the velocity dispersion at matter radiation equality. Density perturbations evolve through three stages: radiation domination when the particle is relativistic and non-relativistic and matter domination. An early ISW effect during the first stage leads to an enhancement of density perturbations and a plateau in the transfer function for k k f s . An effective fluid description emerges at small scales which includes the effects of free streaming in initial conditions and inhomogeneities. The transfer function features WDM-acoustic oscillations at scales k 2 k f s . We study the power spectra for two models of sterile neutrinos with m ∼ keV produced nonresonantly, at the QCD and EW scales respectively. The latter case yields acoustic oscillations on mass scales ∼ 10 8 M ⊙ . Our results reveal a quasi-degeneracy between the mass, distribution function and decoupling temperature suggesting caveats on the constraints on the mass of a sterile neutrino from current WDM N-body simulations and Lyman-α forest data. A simple analytic interpolation of the power spectra between large and small scales and its numerical implementation is given.

We study the production of sterile neutrinos in the region T ∼ MW in an extension beyond the standard model with the see-saw mass matrix originating in Yukawa couplings to Higgs-like scalars with masses and vev's of the order of the electroweak scale. Sterile neutrinos are produced by the decay of scalars and standard model vector bosons. We obtain the index of refraction, dispersion relations, mixing angles in the medium and production rates including those for right-handed sterile neutrinos, from the standard model and beyond the standard model self-energies. For 1 MW /T 3 we find narrow MSW resonances with k T for both left and right handed neutrinos even in absence of a lepton asymmetry in the (active) neutrino sector, as well as very low energy (k/T ≪ |ξ|) narrow MSW resonances in the presence of a lepton asymmetry consistent with the bounds from WMAP and BBN. For small vacuum mixing angle, consistent with observational bounds, the absorptive part of the self-energies lead to a strong damping regime very near the resonances resulting in the exact degeneracy of the propagating modes with a concomitant breakdown of adiabaticity. We argue that cosmological expansion sweeps through the resonances, resonant and non-resonant sterile neutrino production results in a highly non-thermal distribution function enhanced at small momentum k < T , with potentially important consequences for their free streaming length and transfer function at small scales. PACS numbers: 95.35.+d;12.60.Cn;95.30.Cq * Electronic address: juw31@pitt.edu † Electronic address: cmho@berkeley.edu ‡ Electronic address: boyan@pitt.edusatellites. A small scale cutoff in the (DM) power spectrum may also explain the apparent smallness of galaxies at z ∼ 3 found in ref. [25].Although the interpretation of cores in (dSphs) may be challenged by alternative explanations, and the missing satellite problem could be resolved by astrophysical mechanisms such as complex "gastrophysics", and recent simulations suggest that the dynamics of subhalos is not too different in (WDM) and (CDM) models [26], there is an intrinsic interest in studying alternatives to the standard (CDM) paradigm.Any particle physics explanation of (DM) involves extensions beyond the Standard Model (SM), allowing quite generally, both (CDM) and (WDM) candidates.Sterile neutrinos, namely SU (2) singlets, with masses in the ∼ keV range may be suitable (WDM) candidates [27,28,29,30,31,32,33,34,35] and may provide possible solutions to other astrophysical problems [31]. The main property that is relevant for structure formation of any (DM) candidate is its distribution function after decoupling [34,36] which depends on the production mechanism and the quantum kinetic evolution from production to decoupling. Sterile neutrinos may be produced by various different mechanisms [27,28,29,30,31,32,33], among them nonresonant mixing, or Dodelson-Widrow (DW) [27,28,29] has been invoked often. However, there seems to be some tension between the X-ray[38] and the Lyman-α forest data [39,40] leading to th...

In charged current weak interaction processes, neutrinos are produced in an entangled state with the charged lepton. This correlated state is disentangled by the measurement of the charged lepton in a detector at the production site. We study the dynamical aspects of disentanglement, propagation and detection, in particular the conditions under which the disentangled state is a coherent superposition of mass eigenstates. The appearance and disappearance far-detection processes are described from the time evolution of this disentangled "collapsed" state. The familiar quantum mechanical interpretation and factorization of the detection rate emerges when the quantum state is disentangled on time scales much shorter than the inverse oscillation frequency, in which case the final detection rate factorizes in terms of the usual quantum mechanical transition probability provided the final density of states is insensitive to the neutrino energy difference. We suggest possible corrections for short-baseline experiments. If the charged lepton is unobserved, neutrino oscillations and coherence are described in terms of a reduced density matrix obtained by tracing out an un-observed charged lepton. The diagonal elements in the mass basis describe the production of mass eigenstates whereas the off diagonal ones provide a measure of coherence. It is shown that coherences are of the same order of the diagonal terms on time scales up to the inverse oscillation frequency, beyond which the coherences oscillate as a result of the interference between mass eigenstates.

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The dynamics of neutrino mixing and oscillations are studied directly in finite real time in a model that effectively describes charged current weak interactions. Finite time corrections to the S-matrix result for the appearance and disappearance probabilities are obtained. It is observed that these effects may be of the same order of the S-matrix result in long-baseline appearance experiments. We argue that fundamentally, the S-matrix is ill-suited to describe long-baseline events due to the fact that the neutrino is produced in an entangled state with the charged lepton, which can be disentangled by the measurement of the charged lepton near the production site. The appearance and disappearance far-detection process is described from the time evolution of this disentangled "collapsed" state, allowing us to establish the conditions under which factorization of detection rates emerges in long-baseline experiments. We also study the time evolution of the reduced density matrix and show explicitly how oscillations are manifest in the off-diagonal terms, i.e., coherences, as a result of a finite time analysis. Lastly, we study a model for the "GSI anomaly" obtaining the time evolution of the population of parent and daughter particles directly in real time. We confirm that the decay rate of parent and growth rate December 3, 2018 12:39 WSPC/INSTRUCTION FILE nuoscillation-IJMPA-revised of daughters do not feature oscillatory behavior from interference of mass eigenstates.