207 research outputs found
The Three Loop Equation of State of QED at High Temperature
We present the three loop contribution (order ) to the pressure of
massless quantum electrodynamics at nonzero temperature. The calculation is
performed within the imaginary time formalism. Dimensional regularization is
used to handle the usual, intermediate stage, ultraviolet and infrared
singularities, and also to prevent overcounting of diagrams during resummation.Comment: ANL-HEP-PR-94-02, SPhT/94-054 (revised final version
Cosmological Consequences of Slow-Moving Bubbles in First-Order Phase Transitions
In cosmological first-order phase transitions, the progress of true-vacuum
bubbles is expected to be significantly retarded by the interaction between the
bubble wall and the hot plasma. We examine the evolution and collision of
slow-moving true-vacuum bubbles. Our lattice simulations indicate that phase
oscillations, predicted and observed in systems with a local symmetry and with
a global symmetry where the bubbles move at speeds less than the speed of
light, do not occur inside collisions of slow-moving local-symmetry bubbles. We
observe almost instantaneous phase equilibration which would lead to a decrease
in the expected initial defect density, or possibly prevent defects from
forming at all. We illustrate our findings with an example of defect formation
suppressed in slow-moving bubbles. Slow-moving bubble walls also prevent the
formation of `extra defects', and in the presence of plasma conductivity may
lead to an increase in the magnitude of any primordial magnetic field formed.Comment: 10 pages, 7 figures, replaced with typos corrected and reference
added. To appear in Phys. Rev.
Black Hole Chromosphere at the LHC
If the scale of quantum gravity is near a TeV, black holes will be copiously
produced at the LHC. In this work we study the main properties of the light
descendants of these black holes. We show that the emitted partons are closely
spaced outside the horizon, and hence they do not fragment into hadrons in
vacuum but more likely into a kind of quark-gluon plasma. Consequently, the
thermal emission occurs far from the horizon, at a temperature characteristic
of the QCD scale. We analyze the energy spectrum of the particles emerging from
the "chromosphere", and find that the hard hadronic jets are almost entirely
suppressed. They are replaced by an isotropic distribution of soft photons and
hadrons, with hundreds of particles in the GeV range. This provides a new
distinctive signature for black hole events at LHC.Comment: Incorporates changes made for the version to be published in Phys.
Rev. D. Additional details provided on the effect of the chromosphere in
cosmic ray shower
Primordial black holes in braneworld cosmologies: astrophysical constraints
In two recent papers we explored the modifications to primordial black hole
physics when one moves to the simplest braneworld model, Randall--Sundrum type
II. Both the evaporation law and the cosmological evolution of the population
can be modified, and additionally accretion of energy from the background can
be dominant over evaporation at high energies. In this paper we present a
detailed study of how this impacts upon various astrophysical constraints,
analyzing constraints from the present density, from the present high-energy
photon background radiation, from distortion of the microwave background
spectrum, and from processes affecting light element abundances both during and
after nucleosynthesis. Typically, the constraints on the formation rate of
primordial black holes weaken as compared to the standard cosmology if black
hole accretion is unimportant at high energies, but can be strengthened in the
case of efficient accretion.Comment: 17 pages RevTeX4 file with three figures incorporated; final paper in
series astro-ph/0205149 and astro-ph/0208299. Minor changes to match version
accepted by Physical Review
High Energy Colliders as Black Hole Factories: The End of Short Distance Physics
If the fundamental Planck scale is of order a TeV, as the case in some
extra-dimensions scenarios, future hadron colliders such as the Large Hadron
Collider will be black hole factories. The non-perturbative process of black
hole formation and decay by Hawking evaporation gives rise to spectacular
events with up to many dozens of relatively hard jets and leptons, with a
characteristic ratio of hadronic to leptonic activity of roughly 5:1. The total
transverse energy of such events is typically a sizeable fraction of the beam
energy. Perturbative hard scattering processes at energies well above the
Planck scale are cloaked behind a horizon, thus limiting the ability to probe
short distances. The high energy black hole cross section grows with energy at
a rate determined by the dimensionality and geometry of the extra dimensions.
This dependence therefore probes the extra dimensions at distances larger than
the Planck scale.Comment: Latex, 28 pages. v4: minor changes, largely to agree with published
version; appendix added comparing convention
Effect of pre-existing baryon inhomogeneities on the dynamics of quark-hadron transition
Baryon number inhomogeneities may be generated during the epoch when the
baryon asymmetry of the universe is produced, e.g. at the electroweak phase
transition. The regions with excess baryon number will have a lower temperature
than the background temperature of the universe. Also the value of the quark
hadron transition temperature will be different in these regions as
compared to the background region. Since a first-order quark hadron transition
is very susceptible to small changes in temperature, we investigate the effect
of the presence of such baryonic lumps on the dynamics of quark-hadron
transition. We find that the phase transition is delayed in these lumps for
significant overdensities. Consequently, we argue that baryon concentration in
these regions grows by the end of the transition. We briefly discuss some
models which may give rise to such high overdensities at the onset of the
quark-hadron transition.Comment: 16 pages, no figures, minor changes, version to appear in Phys. Rev.
Simulações no CROPGRO/DSSAT do carbono no solo cultivado com soja sob plantio direto e preparo convencional, em clima subtropical do sul do Brasil.
Objetivou-se avaliar o potencial do modelo CROPGRO, inserido no DSSAT v.4,0 (Decision Support System for Agrotechnology Transfer) para simular o carbono no solo, no sistema plantio direto. Os dados foram coletados na Estação Experimental da Universidade Federal do Rio Grande do Sul (EEA/UFRGS), em Eldorado do Sul, durante o ano agrícola 2003/04, num delineamento em faixas, em Argissolo Vermelho distrófico típico. A semeadura da soja (cv. Fepagro RS10 - ciclo longo) ocorreu em 20/11/03 para uma população inicial em torno de 300 mil plantas ha-1. Foram utilizados dois sistemas de manejo do solo: preparo convencional (PC) e sistema plantio direto (PD) irrigados (I) e não irrigados (NI). Foram inseridos no DSSAT dados edáficos, meteorológicos diários e da cultura. Adotou-se o método Ceres, no CROPGROSoja para simular o teor de carbono (C) no solo. As simulações mostraram que há maior estoque de C em plantio direto irrigado em relação ao preparo convencional, demonstrando sensibilidade do CROPGRO-Soja ao manejo do solo. Os mais elevados resíduos de C em solo sob plantio direto evidenciam mitigações de emissões desse gás para a atmosfera em cultivos na região estudada
Phase Equilibration and Magnetic Field Generation in U(1) Bubble Collisions
We present the results of lattice computations of collisions of two expanding
bubbles of true vacuum in the Abelian Higgs model with a first-order phase
transition. New time-dependent analytical solutions for the Abelian field
strength and the phase of the complex field are derived from initial conditions
inferred from linear superposition and are shown to be in excellent agreement
with the numerical solutions especially for the case where the initial phase
difference between the bubbles is small. With a step-function approximation for
the initial phase of the complex field, solutions for the Abelian field
strength and other gauge-invariant quantities are obtained in closed form.
Possible extensions of the solution to the case of the electroweak phase
transition and the generation of primordial magnetic fields are briefly
discussed.Comment: LaTeX, 41 pages, 6 figures, submitted to Physical Review
Effect of Finite Mass on Primordial Nucleosynthesis
We have calculated the small effect of finite nucleon mass on the
weak-interaction rates that interconvert protons and neutrons in the early
Universe. We have modified the standard code for primordial nucleosynthesis to
include these corrections and find a small, systematic increase in the 4He
yield, , depending slightly on the
baryon-to-photon ratio. The fractional changes in the abundances of the other
light elements are a few percent or less for interesting values of the
baryon-to-photon ratio.Comment: 15 pages, 8 figures, uses psfig.st
Fluctuations and Bubble Dynamics in First-Order Phase Transitions
We numerically examine the effect of thermal fluctuations on a first-order
phase transition in 2+1 dimensions. By focusing on the expansion of a single
bubble we are able to calculate changes in the bubble wall's velocity as well
as changes in its structure relative to the standard case where the bubble
expands into a homogeneous background. Not only does the wall move faster, but
the transition from the symmetric to the asymmetric phase is no longer smooth,
even for a fairly strong transition. We discuss how these results affect the
standard picture of electroweak baryogenesis.Comment: Latex, 30 pages, 11 ps figures, short discussion added in conclusions
and minor clarifications, accepted to Phys Rev
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