1,034 research outputs found
Transport coefficients of a unitarized pion gas
The latest experimental results in relativistic heavy-ion collisions show
that the matter there produced requires transport coefficients because of the
important collective properties found. We review the theoretical calculation of
these transport coefficients in the hadron side at low temperatures by
computing them in a gas composed of low energy pions. The interaction of these
pions is taken from an effective chiral theory and further requiring scattering
unitarity. The propagation of D and D* mesons in the thermalized pion gas is
also studied in order to extract the heavy quark diffusion coefficients in the
system.Comment: 7 pages, 3 figures, contribution to the International School of
Nuclear Physics, 33rd Course: From Quarks and Gluons to Hadrons and Nuclei,
Erice-Sicily: 16-24 September 201
On the Equivalence Theorem in the Description of the Symmetry Breaking Sector of the Standard Model
We develop an alternative formulation of the symmetry breaking sector of the
Standard Model as a gauged non-linear sigma model (NLSM) following the
philosophy of the Chiral lagrangian approach, which is the only compatible with
all the experimental and theoretical constraints. We derive the BRS symmetry of
the model and the corresponding quantum lagrangian, which is a generalization
of the standard Faddeev-Popov method, in a way which is covariant with respect
to the reparametrizations of the coset space of the NLSM. Then we use the BRS
invariance of the quantum lagrangian to state the Equivalence Theorem for the
renormalized -matrix elements calculated as a chiral expansion.Comment: LaTeX. Final version as it will appear in Nuclear Physics B (1994
Brout-Englert-Higgs mechanism for accelerating observers
In this work we consider the spontaneous symmetry breaking of the electroweak
gauge group into taken place in the Standard
Model of particle physics as seen from the point of view of an accelerating
observer. According to the Unruh effect that observer detects the Minkowski
vacuum as a thermal bath at a temperature proportional to the proper
acceleration . Then we show that (in a certain large limit) when the
acceleration is bigger than the critical value (where is
the Higgs vacuum expectation value), the electroweak
gauge symmetry is restored and all elementary particles become massless. In
addition, even observers with , can see this symmetry restoration in the
region close to the Rindler horizon
Dark matter clues in the muon anomalous magnetic moment
We study the possibility to explain the non-baryonic dark matter abundance
and improve the present fits on the muon anomalous magnetic moment through the
same new physics. The only viable way to solve simultaneously both problems
which is known to date is by using supersymmetric theories. However in this
work we show that massive brane fluctuations (branons) in large
extra-dimensions models can provide a more economical alternative to
supersymmetry. This is so because the low-energy branon physics depends
effectively on only three parameters. Next collider experiments, such as LHC or
ILC, will be sensitive to branon phenomenology in the natural parameter region
where the theory is able to account for the two effects.Comment: 4 pages, 3 figures, REVTeX
The Equivalence Theorem for Chiral Lagrangians
In this work we derive the version of the Equivalence Theorem that applies
when the symmetry breaking sector of the Standard Model is described by a
general chiral lagrangian. The demonstration is valid for renormalized fields
for any value of the gauge parameter (in gauges) and any
parametrization of the coset space. It is based in the absence of gauge
anomalies which makes it possible to build an (anti)-BRS invariant chiral
lagrangian in terms of the renormalized fields and therefore to use the
corresponding Ward identities to obtain the theorem.Comment: 18 pages, LaTeX, FT/UCM/2/94 (We have corrected some errata
Bulk viscosity of low-temperature strongly interacting matter
We study the bulk viscosity of a pion gas in unitarized Chiral Perturbation
Theory at low and moderate temperatures, below any phase transition to a
quark-gluon plasma phase. We argue that inelastic processes are irrelevant and
exponentially suppressed at low temperatures. Since the system falls out of
chemical equilibrium upon expansion,a pion chemical potential must be
introduced, so we extend the existing theory to include it. We control the zero
modes of the collision operator and Landau's conditions of fit when solving the
Boltzmann equation with the elastic collision kernel. The dependence of the
bulk viscosity with temperature is reminiscent of the findings of
Fernandez-Fraile and Gomez Nicola, while the numerical value is closer to that
of Davesne. In the zero-temperature limit we correctly recover the vanishing
viscosity associated to a non-relativistic monoatomic gas.Comment: 8 pages, 8 figure
Primordial torsion fields as an explanation of the anisotropy in cosmological electromagnetic propagation
In this note we provide a simple explanation of the recent finding of
anisotropy in electromagnetic (EM) propagation claimed by Nodland and Ralston
(astro-ph/9704196). We consider, as a possible origin of such effect, the
effective coupling between EM fields and some tiny background torsion field.
The coupling is obtained after integrating out charged fermions, it is gauge
invariant and does not require the introduction of any new physics.Comment: 8 pages, LaTeX, one figure, enlarged version with minor correction
Study of gamma gamma -> W_L W_L and gamma gamma -> Z_L Z_L reactions with Chiral Lagrangians
We analyze the effects of a strongly interacting symmetry breaking sector of
the Standard Model in and reactions at TeV energies by using Chiral Lagrangians and Chiral
Perturbation Theory. We find significant deviations from the Standard Model
predictions for the differential cross sections at high invariant mass of the
gauge bosons pair. We study the experimental signals that could be obtained in
a high energy and high luminosity dedicated collider and
estimate the sensitivity that such experiments could reach to the values of the
effective lagrangian parameters.Comment: 14 pages, LaTeX, 4 figures (not included), FTUAM92/2
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