6,170 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
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
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Trade Adjustment Assistance (TAA) and Its Role in U.S. Trade Policy
[Excerpt] When Congress passed the Reciprocal Trade Agreements Act (RTAA) of 1934, it reflected an important transition in ânational trade policyâ away from âprotectionismâ toward greater âtrade liberalization.â This shift continues to be the dominant, but hardly uncontested, trade policy of the United States. The substantial national gains from trade have long been recognized, yet trade liberalizing legislation often faces strong political opposition because related costs, although much smaller, affect a vocal and concentrated constituency. Congress first addressed this inherent tension with legislation that allowed for the reimposition of tariffs and other trade barriers when domestic industries were threatened or hurt by imports. In 1962, however, Congress adopted an additional approach by providing trade adjustment assistance (TAA) directly to trade-affected firms and workers. It remains a controversial pillar of U.S. trade policy today.
This report discusses the role of TAA in U.S. trade policy, from its inception as a legislative option in the early 1950s, to its core role as an alternative to import relief that many argue has served to promote the long-term U.S. trade liberalization agenda. It will also consider the extent to which TAA has been linked to both renewal of trade agreements authority, and passage of trade agreement implementing legislation. TAA has become an integral part of an increasingly complex U.S. trade policy. Understanding the origins of TAA, the historical congressional debate, and legislative options considered by Congress over the past 50 years may help inform the current discussion of TAA reauthorization
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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