146 research outputs found
Lattice QCD-based equations of state at vanishing net-baryon density
We present realistic equations of state for QCD matter at vanishing
net-baryon density which embed recent lattice QCD results at high temperatures
combined with a hadron resonance gas model in the low-temperature, confined
phase. In the latter, we allow an implementation of partial chemical
equilibrium, in which particle ratios are fixed at the chemical freeze-out, so
that a description closer to the experimental situation is possible. Given the
present uncertainty in the determination of the chemical freeze-out temperature
from first-principle lattice QCD calculations, we consider different values
within the expected range. The corresponding equations of state can be applied
in the hydrodynamic modeling of relativistic heavy-ion collisions at the LHC
and at the highest RHIC beam energies. Suitable parametrizations of our results
as functions of the energy density are also provided
Lattice QCD-based equations of state at vanishing net-baryon density
We construct a realistic equation of state for QCD matter at vanishing
net-baryon density, which is based on recent lattice QCD results at high
temperatures combined with a hadron resonance gas model in the low-temperature,
confined phase. Partial chemical equilibrium, in which certain particle ratios
are fixed at the chemical freeze-out, can be implemented, allowing a
description closer to the experimental situation. Given the present uncertainty
in the chemical freeze-out temperature, we consider different values within the
expected range. The resulting equations of state can be applied in the
hydrodynamic modeling of relativistic heavy-ion collisions at the LHC and at
the highest RHIC beam energies. Suitable parametrizations of our results are
provided
Determination of freeze-out conditions from fluctuation observables measured at RHIC
We extract chemical freeze-out conditions via a thermal model approach from
fluctuation observables measured at RHIC and compare with results from lattice
QCD and statistical hadronization model fits. The possible influence of
additional critical and non-critical fluctuation sources not accounted for in
our analysis is discussed
Parametrization for chemical freeze-out conditions from net-charge fluctuations measured at RHIC
We discuss details of our thermal model applied to extract chemical
freeze-out conditions from fluctuations in the net-electric charge and
net-proton number measured at RHIC. A parametrization for these conditions as a
function of the beam energy is given
Antiproton fluxes from light neutralinos
We analyze how the measurements of the low-energy spectrum of cosmic
antiprotons can provide information on relic neutralinos. The analysis is
focused on the light neutralinos which emerge in supersymmetric schemes where
gaugino-mass unification is not assumed. We determine which ranges of the
astrophysical parameters already imply stringent constraints on the
supersymmetric configurations and those ranges which make the antiproton flux
sensitive to the primary component generated by the neutralino
self-annihilation. Our results are derived from some general properties of the
antiproton flux proved to be valid for a generic cold dark matter candidate
Species Doublers as Super Multiplet Partners in Lattice Supersymmetry
We propose a new lattice superfield formalism in momentum representation
which accommodates species doublers of the lattice fermions and their bosonic
counterparts as super multiplets. We explicitly show that one dimensional
model with interactions has exact supersymmetry on the lattice for all super
charges with lattice momentum. In coordinate representation the finite
difference operator is made to satisfy Leibnitz rule by introducing a non local
product, the "star" product, and the exact lattice supersymmetry is realized.
Supersymmetric Ward identities are shown to be satisfied at one loop level
Angularities and other shapes
I discuss soft-gluon resummation and power corrections for event shape
distributions, mostly in e+ e- annihilation. I consider specifically the
thrust, the C parameter, and the class of angularities, and show how
factorization techniques and dressed gluon exponentiation lead to predictive
models of power corrections that are firmly grounded in perturbative QCD. The
scaling rule for the shape function for angularities is derived as an example.
Finally, I make a few remarks on possible generalizations to hadron collisions,
and on their relevance to LHC studies
Theoretical issues at LEP2 and LC
After 12 years of glorious data taking LEP has been shut down. During the
past two years an incredible effort has been devoted to get more accurate
predictions and estimates of the related theoretical uncertainties. Many of the
theoretical questions driven by LEP are also relevant at the LC, where
predictions will be needed with even higher accuracy. This is particularly true
for 4-fermion Physics. In this contribution, I review some of the most
important theoretical achievements at LEP in understanding W and Z pair
production, 4-fermion + 1 visible photon signatures and in solving problems
related with gauge invariance. Issues on single W Physics are covered
elsewhere.
Part of the presented work is in progress, the final LEP2 analysis still being
under way
Topics on four-fermion Physics at electron-positron colliders
I review the most recent progresses in the calculation of four-fermion
processes in electron-positron collision
Are Constants Constant?
The prospect of a time-dependent Higgs vacuum expectation value is examined
within the standard model of electroweak interactions. It is shown that the
classical equation of motion for the Higgs field admits a solution that is a
doubly-periodic function of time. The corresponding Dirac equation for the
electron field is equivalent to a second order differential equation with
doubly-periodic coefficients. In the limit of very large primitive period of
the Higgs background this equation can be solved in WKBJ approximation, showing
plane-wave solutions with a time-dependent distortion factor which can be made
arbitrarily small
- …