5,342 research outputs found
A study of the pion effective mass at finite temperature using the linear sigma model
We have used the Cornwall--Jackiw--Tomboulis method of composite operators
and its formulation at finite temperature by Amelino-Camelia and Pi, in order
to calculate the effective potential of the O(4) linear sigma model beyond the
Hartree approximation. We have obtained a system of gap equations for the
effective mass of sigma and the pions as well as for the condensate, the order
parameter of the chiral phase transition. We find that the thermal effective
mass of the pions at low temperatures remains lower than in the Hartree case,
nevertheless deviates from the chiral limit. Our observation is consistent with
other results which have been published previously.Comment: Typos in address and references corrected. Latex2e, 5 pages, 2 .eps
figures. Contribution to the proceedings of the conference: X Hadron Physics
and VII Relativistic Aspects of Nuclear Physics: A joint meeting on QCD and
QGP, (HADRON-RANP 2004), 28 March--3 April 2004, Angra dos Reis, Rio de
Janeiro, Brazi
Baryogenesis at the electroweak phase transition
A possible solution to the observed baryon asymmetry in the universe is
described, based on the physics of the standard model of electroweak
interactions. At temperatures high enough electroweak physics provides
violation of baryon number, while C and CP symmetries are not exactly
conserved, although in the context of the minimal electroweak model with one
Higgs doublet the rate of CP violation is not sufficient enough to generate the
observed asymmetry. The condition that the universe must be out of thermal
equilibrium requires the electroweak phase transition (EWPT) to be first order.
The dynamics of the phase transition in the minimal model is investigated
through the effective potential, which is calculated at the one loop order.
Finite temperature effects on the effective potential are treated numerically
and within the high temperature approximation, which is found to be in good
agreement with the exact calculation. At the one loop level the phase
transition was found to be of the first order, while the strength of the
transition depends on the unknown parameters of the theory which are the Higgs
boson and top quark masses.Comment: 30 pages, 15 eps figures, revtex4, based on MSc thesis report
submitted to Manchester Universit
Linear sigma model at finite temperature
The chiral phase transition is investigated within the framework of thermal
field theory using the O(N) linear sigma model as an effective theory. We
calculate the thermal effective potential by using the
Cornwall-Jackiw-Tomboulis formalism of composite operators. The thermal
effective potential is calculated for N=4 involving as usual the sigma and the
three pions, and in the large-N approximation involving N-1 pion fields. In
both cases, the system of the resulting gap equations for the thermal effective
masses of the particles has been solved numerically, and we have investigated
the evolution of the effective potential. In the N=4 case, there is indication
of a first-order phase transition, while in the large N approximation the phase
transition appears as second-order. In this analysis, we have ignored quantum
fluctuations and have used the imaginary time formalism for calculations. We
have extended our calculation in order to include the full effect of two loops
in the calculation of the effective potential. In this case, the effective
masses are momentum dependent. In order to perform the calculations, we found
the real time formalism to be convenient. We have calculated the effective
masses of pions at the low-temperature phase and we found a quadratic
dependence on temperature, in contrast to the Hartree case, where the mass is
proportional to temperature. The sigma mass was investigated in the presence of
massive pions, and we found a small deviation compared to the Hartree case. In
all cases, the system approaches the behaviour of the ideal gas at the high
temperature limit.Comment: 33 pages, 40 eps figures, based on PhD thesis submitted to Manchester
University in Oct 200
Thermal effective potential of the linear sigma model
We have attempted an approach to the chiral phase transition of QCD using the
linear sigma model as an effective theory. In order to get some insight into
how the phase transition could proceed, we have calculated the finite
temperature effective potential of this model in the Hartree and large N
approximations using the Cornwall-Jackiw-Tomboulis formalism of composite
operators.Comment: 4 pages revtex, 5 eps figures, axodraw.sty, poster presented in the
5th International Workshop on Thermal Field Theories, Regensburg, German
One loop corrections to coupling constants in String Effective Field Theory
In the framework of a recently proposed method for computing exactly string
amplitudes regularized in the infra-red, I determine the one-loop correlators
for auxiliary fields in the symmetric orbifold model. The
-field correlation function turns out to give the one-loop corrections for
the gauge couplings, which amounts to a string-theory supersymmetry Ward
identity. The two-point function for uncharged fields leads to the one-loop
renormalization of the moduli K\"ahler metric, and eventually to the
corrections for the Yukawa couplings.Comment: Plain TeX, 19p
Gravitational duality, topologically massive gravity and holographic fluids
Self-duality in Euclidean gravitational set ups is a tool for finding
remarkable geometries in four dimensions. From a holographic perspective,
self-duality sets an algebraic relationship between two a priori independent
boundary data: the boundary energy-momentum tensor and the boundary Cotton
tensor. This relationship, which can be viewed as resulting from a topological
mass term for gravity boundary dynamics, survives under the Lorentzian
signature and provides a tool for generating exact bulk Einstein spaces
carrying, among others, nut charge. In turn, the holographic analysis exhibits
perfect-fluid-like equilibrium states and the presence of non-trivial vorticity
allows to show that infinite number of transport coefficients vanish.Comment: 37 page
String Theory on AdS3: Some Open Questions
String theory on curved backgrounds has received much attention on account of
both its own interest, and of its relation with gauge theories. Despite the
progress made in various directions, several quite elementary questions remain
unanswered, in particular in the very simple case of three-dimensional anti-de
Sitter space. I will very briefly review these problems, discuss in some detail
the important issue of constructing a consistent spectrum for a string
propagating on ADS3 plus torsion background, and comment on potential
solutions.Comment: 18 pages, latex. To appear in the proceedings of the TMR European
program meeting "Quantum aspects of gauge theories, supersymmetry and
unification", Paris, France, 1--7 September, 1999; v2: comments and
references adde
NS5-branes, holography and CFT deformations
A few supergravity solutions representing configurations of NS5-branes admit
exact conformal field theory (CFT) description. Deformations of these solutions
should be described by exactly marginal operators of the corresponding
theories. We briefly review the essentials of these constructions and present,
as a new case, the operators responsible for turning on angular momentum.Comment: 6 pages, 2 figures, Proceedings contribution to the 9th Hellenic
School on Elementary Particle Physics and Gravity}, Corfu, Greece, September
200
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