2,011 research outputs found
Phase transition dynamics in the hot Abelian Higgs model
We present a detailed numerical study of the equilibrium and non-equilibrium
dynamics of the phase transition in the finite-temperature Abelian Higgs model.
Our simulations use classical equations of motion both with and without
hard-thermal-loop corrections, which take into account the leading quantum
effects. From the equilibrium real-time correlators, we determine the Landau
damping rate, the plasmon frequency and the plasmon damping rate. We also find
that, close to the phase transition, the static magnetic field correlator shows
power-law magnetic screening at long distances. The information about the
damping rates allows us to derive a quantitative prediction for the number
density of topological defects formed in a phase transition. We test this
prediction in a non-equilibrium simulation and show that the relevant time
scale for defect formation is given by the Landau damping rate.Comment: 22 pages, 3 figure
Decay of Magnetic Fields in the Early Universe
We study the evolution of a stochastic helical magnetic field generated in
the early Universe after the electroweak phase transition, using standard
magnetohydrodynamics (MHD). We find how the coherence length xi, magnetic
energy E_M and magnetic helicity H evolve with time. We show that the
self-similarity of the magnetic power spectrum alone implies that xi ~ t^{1/2}.
This in turn implies that magnetic helicity decays as H ~ t^{-2s}, and that the
magnetic energy decays as E_M ~ t^{-0.5-2s}, where s is inversely proportional
to the magnetic Reynolds number Re_M. These laws improve on several previous
estimates.Comment: 5pp LaTeX + World Sci procs class, 3 eps figs. Talk given at Strong
and Electroweak Matter, Oct 2-5 2002, Heidelber
Pressure of the standard model
We review the computation of the thermodynamic pressure of the entire minimal
standard model to three loop order, performed in hep-ph/0510375 and
hep-ph/0512177.Comment: 4 pages, 3 figures, to appear in the proceedings of Strong and
Electroweak Matter 200
A possible origin of superconducting currents in cosmic strings
The scattering and capture of right-handed neutrinos by an Abelian cosmic
string in the SO(10) grand unification model are considered. The scattering
cross-section of neutrinos per unit length due to the interaction with the
gauge and Higgs fields of the string is much larger in its scaling regime than
in the friction one because of the larger infrared cutoff of the former.The
probability of capture in a zero mode of the string accompanied by the emission
of a gauge or Higgs boson shows a resonant peak for neutrino momentum of the
order of its mass. Considering the decrease of number of strings per unit
comoving volume in the scaling epoch the cosmological consequences of the
superconducting strings formed in this regime will be much smaller than those
which could be produced already in the friction one.Comment: 14 pages Latex, 4 figues/ep
Big-bang nucleosynthesis and gamma-ray constraints on cosmic strings with a large Higgs condensate
We consider constraints on cosmic strings from their emission of Higgs particles, in the case that the strings have a Higgs condensate with amplitude of order the string mass scale, assuming that a fraction of the energy of the condensate can be turned into radiation near cusps. The injection of energy by the decaying Higgs particles affects the light element abundances predicted by standard big-bang nucleosynthesis (BBN) and also contributes to the diffuse gamma-ray background (DGRB) in the Universe today. We examine the two main string scenarios (Nambu-Goto and field theory) and find that the primordial helium and deuterium abundances strongly constrain the string tension and the efficiency of the emission process in the NG scenario, while the strongest BBN constraint in the FT scenario comes from the deuterium abundance. The Fermi-LAT measurement of the DGRB constrains the field theory scenario even more strongly than previously estimated from EGRET data, requiring that the product of the string tension μ and Newton’s constant G is bounded by Gμ≲2.7×10−11β−2ft, where β2ft is the fraction of the strings’ energy going into Higgs particles
The bispectrum of matter perturbations from cosmic strings
We present the first calculation of the bispectrum of the matter perturbations induced by cosmic strings. The calculation is performed in two different ways: the first uses the unequal time correlators (UETCs) of the string network - computed using a Gaussian model previously employed for cosmic string power spectra. The second approach uses the wake model, where string density perturbations are concentrated in sheet-like structures whose surface density grows with time. The qualitative and quantitative agreement of the two gives confidence to the results. An essential ingredient in the UETC approach is the inclusion of compensation factors in the integration with the Green's function of the matter and radiation fluids, and we show that these compensation factors must be included in the wake model also. We also present a comparison of the UETCs computed in the Gaussian model, and those computed in the unconnected segment model (USM) used by the standard cosmic string perturbation package CMBACT. We compare numerical estimates for the bispectrum of cosmic strings to those produced by perturbations from an inflationary era, and discover that, despite the intrinsically non-Gaussian nature of string-induced perturbations, the matter bispectrum is unlikely to produce competitive constraints on a population of cosmic strings
Consistent generation of ice-streams via thermo-viscous instabilities modulated by membrane stresses
Accurate computation of ice-stream location and dynamics is a key aspiration for theoretical glaciology. Ice-sheet models with thermo-viscous coupling have been shown to exhibit stream-like instabilities using shallow-ice approximation mechanics, but the location and width of these streams depends on the numerical implementation and are not unique. We present results from thermo-viscously coupled ice-sheet models incorporating membrane stresses. Spontaneous generation of fast-flowing linear features still occurs under certain parameter regimes, with computed stream widths between 20 km to 100 km, comparable with observations. These features are maintained as the grid-size is decreased. The thermo-viscous feedback mechanism that generates ice-streams under the shallow ice approximation still operates, now selecting a unique stream size. Computations of thermo-viscous ice flows should include membrane stresses when the bed is approximately flat, e. g. parts of Antarctica and former ice-sheets of the Northern hemisphere. Previous calculations of spontaneous ice-stream generation using the shallow ice approximation should be reassessed. Citation: Hindmarsh, R. C. A. (2009), Consistent generation of ice-streams via thermo-viscous instabilities modulated by membrane stresses, Geophys. Res. Lett., 36, L06502, doi:10.1029/2008GL036877
Scaling in a SU(2)/Z_3 model of cosmic superstring networks
Motivated by recent developments in superstring theory in the cosmological
context, we examine a field theory which contains string networks with 3-way
junctions. We perform numerical simulations of this model, identify the length
scales of the network that forms, and provide evidence that the length scales
tend towards a scaling regime, growing in proportion to time. We infer that the
presence of junctions does not in itself cause a superstring network to
dominate the energy density of the early Universe.Comment: 12pp, 3 fig
The Thermodynamics of Cosmic String densities in U(1) Scalar Field Theory
We present a full characterization of the phase transition in U(1) scalar
field theory and of the associated vortex string thermodynamics in 3D. We show
that phase transitions in the string densities exist and measure their critical
exponents, both for the long string and the short loops. Evidence for a natural
separation between these two string populations is presented. In particular our
results strongly indicate that an infinite string population will only exist
above the critical temperature. Canonical initial conditions for cosmic string
evolution are show to correspond to the infinite temperature limit of the
theory.Comment: 4 pages, 4 figures, RevTe
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