1,435 research outputs found
A Stochastic Approach to Thermal Fluctuations during a First Order Electroweak Phase Transition
We investigate the role played by subcritical bubbles at the onset of the
electroweak phase transition. Treating the configuration modelling the thermal
fluctuations around the homogeneous zero configuration of the Higgs field as a
stochastic variable, we describe its dynamics by a phenomenological Langevin
equation. This approach allows to properly take into account both the effects
of the thermal bath on the system: a systematic dyssipative force, which tends
to erase out any initial subcritical configuration, and a random stochastic
force responsible for the fluctuations. We show that the contribution to the
variance \lgh\phi^2(t)\rg_V in a given volume from any initial
subcritical configuration is quickly damped away and that, in the limit of long
times, \lgh\phi^2(t)\rg_V approaches its equilibrium value provided by the
stochastic force and independent from the viscosity coefficient, as predicted
by the fluctuation-dissipation theorem. In agreement with some recent claims,
we conclude that thermal fluctuations do not affect the nucleation of critical
bubbles at the onset of the electroweak phase transition making electroweak
baryogenesis scenarios still a viable possibility to explain the primordial
baryon asymmetry in the Universe.Comment: Two figures: fig1.metafile and fig2.metafile. Just print them as
usual file.p
CP Violating Solitons in the Early Universe
Solitons in extensions of the Standard Model can serve as localized sources
of CP violation. Depending on their stability properties, they may serve either
to create or to deplete the baryon asymmetry. The conditions for existence of a
particular soliton candidate, the membrane solution of the two-Higgs model, are
presented. In the generic case, investigated by Bachas and Tomaras, membranes
exist and are metastable for a wide range of parameters. For the more viable
supersymmetric case, it is shown that the present-day existence of CP-violating
membranes is experimentally excluded, but preliminary studies suggest that they
may have existed in the early universe soon after the electroweak phase
transition, with important consequences for the baryon asymmetry of the
universe.Comment: Talk given by Ola Tornkvist, to appear in the proceedings of
Fundamental Physics at the Birth of the Universe, II, in Rome, Italy, 19-24
May 1997. Revtex, 7 pages, 1 postscript figure, uses epsf.tex, aps.sty,
prl.sty, preprint.sty. Preprint number correcte
Clockwork Inflation
We investigate the recently proposed clockwork mechanism delivering light
degrees of freedom with suppressed interactions and show, with various
examples, that it can be efficiently implemented in inflationary scenarios to
generate flat inflaton potentials and small density perturbations without
fine-tunings. We also study the clockwork graviton in de Sitter and,
interestingly, we find that the corresponding clockwork charge is
site-dependent. As a consequence, the amount of tensor modes is generically
suppressed with respect to the standard cases where the clockwork set-up is not
adopted. This point can be made a virtue in resurrecting models of inflation
which were supposed to be ruled out because of the excessive amount of tensor
modes from inflation.Comment: 19 pages, 1 fugur
On the Inflationary Perturbations of Massive Higher-Spin Fields
Cosmological perturbations of massive higher-spin fields are generated during
inflation, but they decay on scales larger than the Hubble radius as a
consequence of the Higuchi bound. By introducing suitable couplings to the
inflaton field, we show that one can obtain statistical correlators of massive
higher-spin fields which remain constant or decay very slowly outside the
Hubble radius. This opens up the possibility of new observational signatures
from inflation.Comment: 22 page
The Halo Mass Function from Excursion Set Theory with a Non-Gaussian Trispectrum
A sizeable level of non-Gaussianity in the primordial cosmological
perturbations may be induced by a large trispectrum, i.e. by a large connected
four-point correlation function. We compute the effect of a primordial
non-Gaussian trispectrum on the halo mass function, within excursion set
theory. We use the formalism that we have developed in a previous series of
papers and which allows us to take into account the fact that, in the presence
of non-Gaussianity, the stochastic evolution of the smoothed density field, as
a function of the smoothing scale, is non-markovian. In the large mass limit,
the leading-order term that we find agrees with the leading-order term of the
results found in the literature using a more heuristic Press-Schecther
(PS)-type approach. Our approach however also allows us to evaluate
consistently the subleading terms, which depend not only on the four-point
cumulant but also on derivatives of the four-point correlator, and which cannot
be obtained within non-Gaussian extensions of PS theory. We perform explicitly
the computation up to next-to-leading order.Comment: LaTeX file, 15 page
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