32 research outputs found
Nonequilibrium quantum fields from first principles
Calculations of nonequilibrium processes become increasingly feasable in
quantum field theory from first principles. There has been important progress
in our analytical understanding based on 2PI generating functionals. In
addition, for the first time direct lattice simulations based on stochastic
quantization techniques have been achieved. The quantitative descriptions of
characteristic far-from-equilibrium time scales and thermal equilibration in
quantum field theory point out new phenomena such as prethermalization. They
determine the range of validity of standard transport or semi-classical
approaches, on which most of our ideas about nonequilibrium dynamics were based
so far. These are crucial ingredients to understand important topical phenomena
in high-energy physics related to collision experiments of heavy nuclei, early
universe cosmology and complex many-body systems.Comment: 10 pages, 5 figures, Acta Phys. Hung. version, minor change
Nonequilibrium Goldstone phenomenon in Hybrid Inflation
We study the onset of Goldstone phenomenon in a hybrid inflation scenario.
The physically motivated range of parameters is analyzed in order to meet the
cosmological constraints. Classical equations of motion are solved and the
evolution through the spontaneous symmetry breaking is followed. We emphasize
the role of topological defects that partially maintain the disordered phase
well after the waterfall. We study the emergence of the Goldstone excitations
and their role in the onset of the radiation dominated universe.Comment: 10 pages with 7 figures. Contribution to Strong and Electroweak
Matter (Heidelberg, 2002
Fate of the classical false vacuum
Thermalisation of configurations with initial white noise power spectrum is
studied in numerical simulations of a classical one-component theory
in 2+1 dimensions, coupled to a small amplitude homogenous external field. The
study is performed for energy densities corresponding to the broken symmetry
phase of the system in equilibrium. The effective equation of the order
parameter motion is reconstructed from its trajectory which starts from an
initial value near the metastable point and ends in the stable ground state.
This phenomenological theory quantitatively accounts for the decay of the false
vacuum. The large amplitude transition of the order parameter between the two
minima displays characteristics reflecting dynamical aspects of the Maxwell
construction.Comment: RevTeX 16 pages, 10 Postscript figures, version accepted in Phys.
Rev.
Lattice SU(3) thermodynamics and the onset of perturbative behaviour
We present the equation of state (pressure, trace anomaly, energy density and
entropy density) of the SU(3) gauge theory from lattice field theory in an
unprecedented precision and temperature range. We control both finite size and
cut-off effects. The studied temperature window () stretches
from the glueball dominated system into the perturbative regime, which allows
us to discuss the range of validity of these approaches. From the critical
couplings on fine lattices we get T_c/\Lambdamsbar=1.26(7) and use this ratio
to express the perturbative free energy in units. We also determine the
preferred renormalization scale of the Hard Thermal Loop scheme and we fit the
unknown order perturbative coefficient at extreme high temperatures
. We furthermore quantify the nonperturbative contribution to the
trace anomaly using two simple functional forms.Comment: 7 pages, Contribution to the The XXVIII International Symposium on
Lattice Field Theory; June 14 - 19, 2010, Villasimius, Sardinia, Ital
Topological features of the deconfinement transition
The first order transition between the confining and the center symmetry
breaking phases of the SU(3) Yang-Mills theory is marked by discontinuities in
various thermodynamics functions, such as the energy density or the value of
the Polyakov loop. We investigate the non-analytical behaviour of the
topological susceptibility and its higher cumulant around the transition
temperature and make the connection to the curvature of the phase diagram in
the plane and to the latent heat.Comment: 13 pages, 10 figure
Ab-initio calculation of the proton and the neutron's scalar couplings for new physics searches
Many low-energy, particle-physics experiments seek to reveal new fundamental
physics by searching for very rare scattering events on atomic nuclei. The
interpretation of their results requires quantifying the non-linear effects of
the strong interaction on the spin-independent couplings of this new physics to
protons and neutrons. Here we present a fully-controlled, ab-initio calculation
of these couplings to the quarks within those constituents of nuclei. We use
lattice quantum chromodynamics computations for the four lightest species of
quarks and heavy-quark expansions for the remaining two. We determine each of
the six quark contributions with an accuracy better than 15%. Our results are
especially important for guiding and interpreting experimental searches for our
universe's dark matter.Comment: 39 pages, 13 figure
Hadronic vacuum polarization contribution to the anomalous magnetic moments of leptons from first principles
We compute the leading, strong-interaction contribution to the anomalous
magnetic moment of the electron, muon and tau using lattice quantum
chromodynamics (QCD) simulations. Calculations include the effects of , ,
and quarks and are performed directly at the physical values of the
quark masses and in volumes of linear extent larger than . All
connected and disconnected Wick contractions are calculated. Continuum limits
are carried out using six lattice spacings. We obtain
,
and
, where the first error
is statistical and the second is systematic.Comment: 17 pages, 8 figures (in 13 PDF files), RevTeX 4.1. Minor changes to
results and to text. References updated. Matches version published in
Physical Review Letter
The approach to thermalization in the classical phi^4 theory in 1+1 dimensions: energy cascades and universal scaling
We study the dynamics of thermalization and the approach to equilibrium in
the classical phi^4 theory in 1+1 spacetime dimensions. At thermal equilibrium
we exploit the equivalence between the classical canonical averages and
transfer matrix quantum traces of the anharmonic oscillator to obtain exact
results for the temperature dependence of several observables, which provide a
set of criteria for thermalization. We find that the Hartree approximation is
remarkably accurate in equilibrium. The non-equilibrium dynamics is studied by
numerically solving the equations of motion in light-cone coordinates for a
broad range of initial conditions and energy densities.The time evolution is
described by several stages with a cascade of energy towards the ultraviolet.
After a transient stage, the spatio-temporal gradient terms become larger than
the nonlinear term and a stage of universal cascade emerges.This cascade starts
at a time scale t_0 independent of the initial conditions (except for very low
energy density). Here the power spectra feature universal scaling behavior and
the front of the cascade k(t) grows as a power law k(t) sim t^alpha with alpha
lesssim 0.25. The wake behind the cascade is described as a state of Local
Thermodynamic Equilibrium (LTE) with all correlations being determined by the
equilibrium functional form with an effective time dependent temperatureTeff(t)
which slowly decreases as sim t^{-alpha}.Two well separated time scales emerge
while Teff(t) varies slowly, the wavectors in the wake with k < k(t) attain LTE
on much shorter time scales.This universal scaling stage ends when the front of
the cascade reaches the cutoff at a time t_1 sim a^{-1/alpha}. Virialization
starts to set much earlier than LTE. We find that strict thermalization is
achieved only for an infinite time scale.Comment: relevance for quantum field theory discussed providing validity
criteria. To appear in Phys. Rev.
Ab initio calculation of the neutron-proton mass difference
The existence and stability of atoms rely on the fact that neutrons are more massive than protons. The measured mass difference is only 0.14% of the average of the two masses. A slightly smaller or larger value would have led to a dramatically different universe. Here, we show that this difference results from the competition between electromagnetic and mass isospin breaking effects. We performed lattice quantum-chromodynamics and quantum-electrodynamics computations with four nondegenerate Wilson fermion flavors and computed the neutron-proton mass-splitting with an accuracy of 300 kilo-electron volts, which is greater than 0 by 5 standard deviations. We also determine the splittings in the Sigma, Xi, D, and Xi(cc) isospin multiplets, exceeding in some cases the precision of experimental measurements
Isospin splittings in the light-baryon octet from lattice QCD and QED
While electromagnetic and up-down quark mass difference effects on octet
baryon masses are very small, they have important consequences. The stability
of the hydrogen atom against beta decay is a prominent example. Here we include
these effects by adding them to valence quarks in a lattice QCD calculation
based on simulations with 5 lattice spacings down to 0.054 fm,
lattice sizes up to 6 fm and average up-down quark masses all the way down to
their physical value. This allows us to gain control over all systematic
errors, except for the one associated with neglecting electromagnetism in the
sea. We compute the octet baryon isomultiplet mass splittings, as well as the
individual contributions from electromagnetism and the up-down quark mass
difference. Our results for the total splittings are in good agreement with
experiment.Comment: 5 pages, 3 figures. Version accepted for publication by Phys. Rev.
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