555 research outputs found
Particle Currents in a Space-Time dependent and CP-violating Higgs Background: a Field Theory Approach
Motivated by cosmological applications like electroweak baryogenesis, we
develop a field theoretic approach to the computation of particle currents on a
space-time dependent and CP-violating Higgs background. We consider the
Standard Model model with two Higgs doublets and CP violation in the scalar
sector, and compute both fermionic and Higgs currents by means of an expansion
in the background fields. We discuss the gauge dependence of the results and
the renormalization of the current operators, showing that in the limit of
local equilibrium, no extra renormalization conditions are needed in order to
specify the system completely.Comment: 21 pages, LaTeX file, uses epsf.sty. 4 figures available as a
compressed .ep
Flux vacua in DBI type Einstein-Maxwell theory
We study compactification of extra dimensions in a theory of
Dirac-Born-Infeld (DBI) type gravity. We investigate the solution for Minkowski
spacetime with an extra space as well as that for de Sitter spacetime
() with an extra space. They are derived by the effective potential
method in the presence of the magnetic flux on the extra sphere. We also
consider the higher dimensional generalization of the solutions. We find that,
in a certain model, the radius of the extra space has a minimum value
independent of the higher-dimensional Newton constant in weak-field limit.Comment: 13 pages, no figure. A reference added, typos fixe
Hairy black holes in theories with massive gravitons
This is a brief survey of the known black hole solutions in the theories of
ghost-free bigravity and massive gravity. Various black holes exist in these
theories, in particular those supporting a massive graviton hair. However, it
seems that solutions which could be astrophysically relevant are the same as in
General Relativity, or very close to them. Therefore, the no-hair conjecture
essentially applies, and so it would be hard to detect the graviton mass by
observing black holes.Comment: References added. 20 pages, 3 figures, based on the talk given at the
7-th Aegean Summer School "Beyond Einstein's theory of gravity", September
201
Thermal Stability of Corrugated Epitaxial Graphene Grown on Re(0001)
We report on a novel approach to determine the relationship between the corrugation and the thermal stability of epitaxial graphene grown on a strongly interacting substrate. According to our density functional theory calculations, the C single layer grown on Re(0001) is strongly corrugated, with a buckling of 1.6 angstrom, yielding a simulated C 1s core level spectrum which is in excellent agreement with the experimental one. We found that corrugation is closely knit with the thermal stability of the C network: C-C bond breaking is favored in the strongly buckled regions of the moire cell, though it requires the presence of diffusing graphene layer vacancies
Bosonic Thermal Masses in Supersymmetry
Effective thermal masses of bosonic particles in a plasma play an important
role in many different phenomena. We compute them in general supersymmetric
models at leading order. The origin of different corrections is explicitly
shown for the formulas to be applicable when some particles decouple. The
correct treatment of Boltzmann decoupling in the presence of trilinear
couplings and mass mixing is also discussed. As a relevant example, we present
results for the Minimal Supersymmetric Standard Model.Comment: 20 pages, LaTeX, plus one postscript figur
Information and Discrimination from b Quark Production on Z Resonance
We introduce and define operatively in a model independent way a new ``heavy"
b-vertexparameter, , that can be derived from the measurement of a
special polarization asymmetry for production of b-quarks on Z resonance. We
show that the combination of the measurement of with that of a second
and previously defined ``heavy" b-vertex parameter can
discriminate a number of models of New Physics that remain associated to
different ``trajectories" in the plane of the variations of the two parameters.
This is shown in particular for some popular SUSY and technicolor-type models.
In general, this discrimination is possible if a measurement of
\underline{both} parameters is performed.Comment: 22 pages, 6 figures available by air mail upon request, (e-mail
[email protected] PM/94-04, UTS-DFT-94-02 .( revised version
with corrected references
Black or red phosphorus yields the same blue phosphorus film
After the discovery of graphene, many other 2D materials have been predicted theoretically and successfully prepared. In this context, single-sheet black phosphorus - phosphorene - is emerging as a viable contender in the field of (2D) semiconductors. Phosphorene offers high carrier mobility and an anisotropic structure that gives rise to a modulation of physical and chemical properties. This opens the way to many novel and fascinating applications related to field-effect transistors and optoelectronic devices. In previous studies, a single layer of blue phosphorene intermixed with Au atoms was grown using purified black phosphorus as a precursor. Starting from the observation that phosphorus vapor mainly consists of P clusters, in this work we aimed at obtaining blue phosphorus using much less expensive purified red phosphorus as an evaporant. By means of microscopy, spectroscopy and diffraction experiments, we show that black or red phosphorus deposition on Au(111) substrates yields the same blue phosphorus film
Fermion scattering off electroweak phase transition kink walls with hypermagnetic fields
We study the scattering of fermions off a finite width kink wall during the
electroweak phase transition in the presence of a background hypermagnetic
field. We derive and solve the Dirac equation for such fermions and compute the
reflection and transmission coefficients for the case when the fermions move
from the symmetric to the broken symmetry phase. We show that the chiral nature
of the fermion coupling with the background field in the symmetric phase
generates an axial asymmetry in the scattering processes. We discuss possible
implications of such axial charge segregation for baryon number generation.Comment: 9 pages, 3 Postscript figures, uses RevTeX4. Expanded discussion,
published versio
On the Importance of Electroweak Corrections for Majorana Dark Matter Indirect Detection
Recent analyses have shown that the inclusion of electroweak corrections can
alter significantly the energy spectra of Standard Model particles originated
from dark matter annihilations. We investigate the important situation where
the radiation of electroweak gauge bosons has a substantial influence: a
Majorana dark matter particle annihilating into two light fermions. This
process is in p-wave and hence suppressed by the small value of the relative
velocity of the annihilating particles. The inclusion of electroweak radiation
eludes this suppression and opens up a potentially sizeable s-wave contribution
to the annihilation cross section. We study this effect in detail and explore
its impact on the fluxes of stable particles resulting from the dark matter
annihilations, which are relevant for dark matter indirect searches. We also
discuss the effective field theory approach, pointing out that the opening of
the s-wave is missed at the level of dimension-six operators and only encoded
by higher orders.Comment: 25 pages, 6 figures. Minor corrections to match version published in
JCA
Resonant Amplification of Electroweak Baryogenesis at Preheating
We explore viable scenarios for parametric resonant amplification of
electroweak (EW) gauge fields and Chern-Simons number during preheating,
leading to baryogenesis at the electroweak (EW) scale. In this class of
scenarios time-dependent classical EW gauge fields, essentially
spatially-homogeneous on the horizon scales, carry Chern-Simons number which
can be amplified by parametric resonance up to magnitudes at which unsuppressed
topological transitions in the Higgs sector become possible. Baryon number
non-conservation associated with the gauge sector and the highly
non-equilibrium nature of preheating allow for efficient baryogenesis. The
requisite large CP violation can arise either from the time dependence of a
slowly varying Higgs field (spontaneous baryogenesis), or from a resonant
amplification of CP violation induced in the gauge sector through loops. We
identify several CP violating operators in the Standard Model and its minimal
extensions that can facilitate efficient baryogenesis at preheating, and show
how to overcome would-be exponential suppression of baryogenesis associated
with tunneling barriers.Comment: 51 pages, 8 figues; minor corrections; references adde
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