5,241 research outputs found
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
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
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
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
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
Extended Ultraviolet Disks and Ultraviolet-bright Disks in Low-mass E/S0 Galaxies
We have identified 15 extended ultraviolet (XUV) disks in a largely field sample of 38 E/S0 galaxies that have stellar masses primarily below ~4 × 10^(10) M_☉ and comparable numbers on the red and blue sequences. We use a new purely quantitative XUV-disk definition designed with reference to the "Type 1" XUV-disk definition found in the literature, requiring UV extension relative to a UV-defined star formation threshold radius. The 39% ± 9% XUV-disk frequency for these E/S0s is roughly twice the ~20% reported for late-type galaxies (although differences in XUV-disk criteria complicate the comparison), possibly indicating that XUV disks are preferentially associated with galaxies experiencing weak or inefficient star formation. Consistent with this interpretation, we find that the XUV disks in our sample do not correlate with enhanced outer-disk star formation as traced by blue optical outer-disk colors. However, UV-Bright (UV-B) disk galaxies with blue UV colors outside their optical 50% light radii do display enhanced optical outer-disk star formation as well as enhanced atomic gas content. UV-B disks occur in our E/S0s with a 42^(+9)_–8% frequency and need not coincide with XUV disks; thus their combined frequency is 61% ± 9%. For both XUV and UV-B disks, UV colors typically imply <1 Gyr ages, and most such disks extend beyond the optical R_(25) radius. XUV disks occur over the full sample mass range and on both the red and blue sequences, suggesting an association with galaxy interactions or another similarly general evolutionary process. In contrast, UV-B disks favor the blue sequence and may also prefer low masses, perhaps reflecting the onset of cold-mode gas accretion or another mass-dependent evolutionary process. Virtually all blue E/S0s in the gas-rich regime below stellar mass M_t ~ 5 × 10^9 M_☉ (the "gas-richness threshold mass") display UV-B disks, supporting the previously suggested association of this population with active disk growth
Three-dimensional U(1) gauge+Higgs theory as an effective theory for finite temperature phase transitions
We study the three-dimensional U(1)+Higgs theory (Ginzburg-Landau model) as
an effective theory for finite temperature phase transitions from the 1 K scale
of superconductivity to the relativistic scales of scalar electrodynamics. The
relations between the parameters of the physical theory and the parameters of
the 3d effective theory are given. The 3d theory as such is studied with
lattice Monte Carlo techniques. The phase diagram, the characteristics of the
transition in the first order regime, and scalar and vector correlation lengths
are determined. We find that even rather deep in the first order regime, the
transition is weaker than indicated by 2-loop perturbation theory. Topological
effects caused by the compact formulation are studied, and it is demonstrated
that they vanish in the continuum limit. In particular, the photon mass
(inverse correlation length) is observed to be zero within statistical errors
in the symmetric phase, thus constituting an effective order parameter.Comment: 42 pages, 14 figure
A quantum jump description for the non-Markovian dynamics of the spin-boson model
We derive a time-convolutionless master equation for the spin-boson model in
the weak coupling limit. The temporarily negative decay rates in the master
equation indicate short time memory effects in the dynamics which is explicitly
revealed when the dynamics is studied using the non-Markovian jump description.
The approach gives new insight into the memory effects influencing the spin
dynamics and demonstrates, how for the spin-boson model the the co-operative
action of different channels complicates the detection of memory effects in the
dynamics.Comment: 9 pages, 6 figures, submitted to Proceedings of CEWQO200
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