231 research outputs found
GeV-scale hot sterile neutrino oscillations: a numerical solution
The scenario of baryogenesis through GeV-scale sterile neutrino oscillations
is governed by non-linear differential equations for the time evolution of a
sterile neutrino density matrix and Standard Model lepton and baryon
asymmetries. By employing up-to-date rate coefficients and a non-perturbatively
estimated Chern-Simons diffusion rate, we present a numerical solution of this
system, incorporating the full momentum and helicity dependences of the density
matrix. The density matrix deviates significantly from kinetic equilibrium,
with the IR modes equilibrating much faster than the UV modes. For equivalent
input parameters, our final results differ moderately (~50%) from recent
benchmarks in the literature. The possibility of producing an observable baryon
asymmetry is nevertheless confirmed. We illustrate the dependence of the baryon
asymmetry on the sterile neutrino mass splitting and on the CP-violating phase
measurable in active neutrino oscillation experiments.Comment: 26 pages. v2: clarifications and references adde
GeV-scale hot sterile neutrino oscillations: a derivation of evolution equations
Starting from operator equations of motion and making arguments based on a
separation of time scales, a set of equations is derived which govern the
non-equilibrium time evolution of a GeV-scale sterile neutrino density matrix
and active lepton number densities at temperatures T > 130 GeV. The density
matrix possesses generation and helicity indices; we demonstrate how helicity
permits for a classification of various sources for leptogenesis. The
coefficients parametrizing the equations are determined to leading order in
Standard Model couplings, accounting for the LPM resummation of 1+n 2+n
scatterings and for all 2 2 scatterings. The regime in which sphaleron
processes gradually decouple so that baryon plus lepton number becomes a
separate non-equilibrium variable is also considered.Comment: 33 pages. v2: clarifications added; published versio
Sterile neutrino dark matter via GeV-scale leptogenesis?
It has been proposed that in a part of the parameter space of the Standard
Model completed by three generations of keV...GeV right-handed neutrinos,
neutrino masses, dark matter, and baryon asymmetry can be accounted for
simultaneously. Here we numerically solve the evolution equations describing
the cosmology of this scenario in a 1+2 flavour situation at temperatures GeV, taking as initial conditions maximal lepton asymmetries produced
dynamically at higher temperatures, and accounting for late entropy and lepton
asymmetry production as the heavy flavours fall out of equilibrium and decay.
For 7 keV dark matter mass and other parameters tuned favourably,
of the observed abundance can be generated. Possibilities for increasing the
abundance are enumerated.Comment: 20 page
Precision study of GeV-scale resonant leptogenesis
Low-scale leptogenesis is most efficient in the limit of an extreme mass
degeneracy of right-handed neutrino flavours. Two variants of this situation
are of particular interest: large neutrino Yukawa couplings, which boost the
prospects of experimental scrutiny, and small ones, which may lead to large
lepton asymmetries surviving down to T < 5 GeV. We study benchmarks of these
cases within a "complete" framework which tracks both helicity states of
right-handed neutrinos as well as their kinetic non-equilibrium, and includes a
number of effects not accounted for previously. For two right-handed flavours
with GeV-scale masses, Yukawa couplings up to are
found to be viable for baryogenesis, with as the
optimal degeneracy. Late-time lepton asymmetries are most favourably produced
with . We show that the system reaches a stationary
state at T < 15 GeV, in which lepton asymmetries can be more than times
larger than the baryon asymmetry, reach flavour equilibrium, and balance
against helicity asymmetries.Comment: 43 pages. v2: improvements in presentation, published versio
Neutrino dynamics below the electroweak crossover
We estimate the thermal masses and damping rates of active (m < eV) and
sterile (M ~ GeV) neutrinos with thermal momenta k ~ 3T at temperatures below
the electroweak crossover (5 GeV < T < 160 GeV). These quantities fix the
equilibration or "washout" rates of Standard Model lepton number densities.
Sterile neutrinos interact via direct scatterings mediated by Yukawa couplings,
and via their overlap with active neutrinos. Including all leading-order
reactions we find that the washout rate generally exceeds the Hubble rate for 5
GeV < T < 30 GeV. Therefore it is challenging to generate a large lepton
asymmetry facilitating dark matter computations operating at T < 5 GeV, whereas
the generation of a baryon asymmetry at T > 130 GeV remains an option. Our
differential rates are tabulated in a form suitable for studies of specific
scenarios with given neutrino Yukawa matrices.Comment: 42 pages. v2: references and clarifications adde
Lattice constraints on the thermal photon rate
We estimate the photon production rate from an SU(3) plasma at temperatures
of about 1.1Tc and 1.3Tc. Lattice results for the vector current correlator at
spatial momenta k ~ (2-6)T are extrapolated to the continuum limit and analyzed
with the help of a polynomial interpolation for the corresponding spectral
function, which vanishes at zero frequency and matches to high-precision
perturbative results at large invariant masses. For small invariant masses the
interpolation is compared with the NLO weak-coupling result, hydrodynamics, and
a holographic model. At vanishing invariant mass we extract the photon rate
which for k \gsim 3T is found to be close to the NLO weak-coupling prediction.
For k \lsim 2T uncertainties remain large but the photon rate is likely to fall
below the NLO prediction, in accordance with the onset of a strongly
interacting behaviour characteristic of the hydrodynamic regime.Comment: 20 pages. v2: clarifications adde
GSE, data management system programmers/User' manual
The GSE data management system is a computerized program which provides for a central storage source for key data associated with the mechanical ground support equipment (MGSE). Eight major sort modes can be requested by the user. Attributes that are printed automatically with each sort include the GSE end item number, description, class code, functional code, fluid media, use location, design responsibility, weight, cost, quantity, dimensions, and applicable documents. Multiple subsorts are available for the class code, functional code, fluid media, use location, design responsibility, and applicable document categories. These sorts and how to use them are described. The program and GSE data bank may be easily updated and expanded
Seawater intrusion and coastal groundwater resources management. Examples from two Mediterranean regions: Catalonia and Sardinia
Seawater intrusion is a natural phenomenon that allows the encroachment of saline water into aquifers. Nevertheless, many human actions along the coastline, in particular groundwater withdrawal, enhance this process and finally cause the salinization of groundwater resources. Here we review the hydrogeological basis of seawater intrusion and describe specific cases in Catalonia and Sardinia, as examples of environmental problems and water management actions. We emphasize the origin of salinization and the hydrogeological details of each case, as well as the solutions that have been implemented to prevent groundwater salinization
Gravitational wave background from Standard Model physics: complete leading order
We compute the production rate of the energy density carried by gravitational waves emitted by a Standard Model plasma in thermal equilibrium, consistently to leading order in coupling constants for momenta k ⌠ÏT. Summing up the contributions from the full history of the universe, the highest temperature of the radiation epoch can be constrained by the so-called Neff parameter. The current theoretical uncertainty âNeff†10â3 corresponds to Tmax†2 Ă 1017 GeV. In the course of the computation, we show how a subpart of the production rate can be determined with the help of standard packages, even if subsequently an IR subtraction and thermal resummation need to be implemented
Quarkonium in Hot Medium
I review recent progress in studying quarkonium properties in hot medium as
well as possible consequences for quarkonium production in heavy ion
collisions.Comment: Invited talk at SQM 2009, Buzios, Brazil, Sep. 27 -Oct. 2 2009,
LaTeX, 8 pages,3 figures; typos corrected, references adde
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