538 research outputs found
An application of the renormalization group to the calculation of the vacuum decay rate in flat and curved space-time
I show that an application of renormalization group arguments may lead to
significant corrections to the vacuum decay rate for phase transitions in flat
and curved space-time. It can also give some information regarding its
dependence on the parameters of the theory, including the cosmological constant
in the case of decay in curved space-time.Comment: 10 pages, LaTeX, various comments and references adde
Derivative expansion and gauge independence of the false vacuum decay rate in various gauges
In theories with radiative symmetry breaking, the calculation of the false
vacuum decay rate requires the inclusion of higher-order terms in the
derivative expansion of the effective action. I show here that, in the case of
covariant gauges, the presence of infrared singularities forbids the consistent
calculation by keeping the lowest-order terms. The situation is remedied,
however, in the case of gauges. Using the Nielsen identities I show
that the final result is gauge independent for generic values of the gauge
parameter that are not anomalously small.Comment: Some comments and references adde
Symmetry breaking and restoration in Lifshitz type theories
We consider the one-loop effective potential at zero and finite temperature
in scalar field theories with anisotropic space-time scaling. For , there
is a symmetry breaking term induced at one-loop at zero temperature and we find
symmetry restoration through a first-order phase transition at high
temperature. For , we considered at first the case with a positive mass
term at tree level and found no symmetry breaking effects induced at one-loop,
and then we study the case with a negative mass term at tree level where we
cannot conclude about symmetry restoration effects at high temperature because
of the imaginary parts that appear in the effective potential for small values
of the scalar field.Comment: 11 pages, 2 figures, version accepted in Physics Letters
Symmetry breaking and restoration for interacting scalar and gauge fields in Lifshitz type theories
We consider the one-loop effective potential at zero and finite temperature
in field theories with anisotropic space-time scaling, with critical exponent
, including both scalar and gauge fields. Depending on the relative
strength of the coupling constants for the gauge and scalar interactions, we
find that there is a symmetry breaking term induced at one-loop at zero
temperature and we find symmetry restoration through a first-order phase
transition at high temperature.Comment: 12 pages, 2 figures, final version accepted in Phys. Let
Hard thermal loops with a background plasma velocity
I consider the calculation of the two and three-point functions for QED at
finite temperature in the presence of a background plasma velocity. The final
expressions are consistent with Lorentz invariance, gauge invariance and
current conservation, pointing to a straightforward generalization of the hard
thermal loop formalism to this physical situation. I also give the resulting
expression for the effective action and identify the various terms.Comment: 11 pages, no figure
Plasmon interactions in the quark-gluon plasma
Yang-Mills theory at finite temperature is rewritten as a theory of plasmons
which provides a Hamiltonian framework for perturbation theory with resummation
of hard thermal loops.Comment: 12 pages, LaTeX, minor typos corrected, discussion adde
A Finite Element Model of the Breast for Predicting Mechanical Deformations during Biopsy Procedures
Currently, High Field (1.5T) Superconducting MR image-guided needle breast procedures allow the physician only to calculate approximately the location and extent of a cancerous tumor in the compressed patient breast before inserting the needle. It can then become relatively uncertain that the tissue specimen removed during the biopsy actually belongs to the lesion of interest. A new method for guiding clinical breast biopsy is presented, based on a deformable finite element model of the breast. The geometry of the model is constructed from MR data, and its mechanical properties are modeled using a non-linear material model. This method allows imaging the breast without compression before the procedure, then compressing the breast and using the finite element model to predict the tumor’s position during the procedure
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