1,230 research outputs found
The back reaction and the effective Einstein's equation for the Universe with ideal fluid cosmological perturbations
We investigate the back reaction of cosmological perturbations on the
evolution of the Universe using the renormalization group method. Starting from
the second order perturbed Einstein's equation, we renormalize a scale factor
of the Universe and derive the evolution equation for the effective scale
factor which includes back reaction due to inhomogeneities of the Universe. The
resulting equation has the same form as the standard Friedman-Robertson-Walker
equation with the effective energy density and pressure which represent the
back reaction effect.Comment: 16 pages, to appear in Phys. Rev.
Postmodern String Theory: Stochastic Formulation
In this paper we study the dynamics of a statistical ensemble of strings,
building on a recently proposed gauge theory of the string geodesic field. We
show that this stochastic approach is equivalent to the Carath\'eodory
formulation of the Nambu-Goto action, supplemented by an averaging procedure
over the family of classical string world-sheets which are solutions of the
equation of motion. In this new framework, the string geodesic field is
reinterpreted as the Gibbs current density associated with the string
statistical ensemble. Next, we show that the classical field equations derived
from the string gauge action, can be obtained as the semi-classical limit of
the string functional wave equation. For closed strings, the wave equation
itself is completely analogous to the Wheeler-DeWitt equation used in quantum
cosmology. Thus, in the string case, the wave function has support on the space
of all possible spatial loop configurations. Finally, we show that the string
distribution induces a multi-phase, or {\it cellular} structure on the
spacetime manifold characterized by domains with a purely Riemannian geometry
separated by domain walls over which there exists a predominantly Weyl
geometry.Comment: 24pages, ReVTe
Emergent electrodynamics from the Nambu model for spontaneous Lorentz symmetry breaking
After imposing the Gauss law constraint as an initial condition upon the
Hilbert space of the Nambu model, in all its generic realizations, we recover
QED in the corresponding non-linear gauge A_{\mu}A^{\mu}=n^{2}M^{2}. Our result
is non-perturbative in the parameter M for n^{2}\neq 0 and can be extended to
the n^{2}=0 case. This shows that in the Nambu model, spontaneous Lorentz
symmetry breaking dynamically generates gauge invariance, provided the Gauss
law is imposed as an initial condition. In this way electrodynamics is
recovered, with the photon being realized as the Nambu-Goldstone modes of the
spontaneously broken symmetry, which finally turns out to be non-observableComment: 17 page
Volume Expansion of Swiss-Cheese Universe
In order to investigate the effect of inhomogeneities on the volume expansion
of the universe, we study modified Swiss-Cheese universe model. Since this
model is an exact solution of Einstein equations, we can get an insight into
non-linear dynamics of inhomogeneous universe from it. We find that
inhomogeneities make the volume expansion slower than that of the background
Einstein-de Sitter universe when those can be regarded as small fluctuations in
the background universe. This result is consistent with the previous studies
based on the second order perturbation analysis. On the other hand, if the
inhomogeneities can not be treated as small perturbations, the volume expansion
of the universe depends on the type of fluctuations. Although the volume
expansion rate approaches to the background value asymptotically, the volume
itself can be finally arbitrarily smaller than the background one and can be
larger than that of the background but there is an upper bound on it.Comment: 22 pages, 7 figures, to be submitted to Phys. Rev.
The vacuum structure in a supersymmetric gauged Nambu-Jona-Lasinio model
The dynamical breakdown of the symmetry triggered by a
top-antitop condensate is studied in a supersymmetric version of the gauged
Nambu-Jona-Lasinio model. An effective potential approach is used to
investigate the vacuum structure and the equivalence with the minimal
supersymmetric standard model. The role of the soft supersymmetry breaking
terms is analyzed in detail in a version of the model where the electroweak
gauge interactions are turned off.Comment: 32 pages (+2 figures not included), Latex, LPTHE 93/0
Back Reaction Problem in the Inflationary Universe
We investigate the back reaction of cosmological perturbations on an
inflationary universe using the renormalization-group method. The second-order
zero mode solution which appears by the nonlinearity of the Einstein equation
is regarded as a secular term of a perturbative expansion, we renormalized a
constant of integration contained in the background solution and absorbed the
secular term to this constant in a gauge-invariant manner. The resultant
renormalization-group equation describes the back reaction effect of
inhomogeneity on the background universe. For scalar type classical
perturbation, by solving the renormalization-group equation, we find that the
back reaction of the long wavelength fluctuation works as a positive spatial
curvature, and the short wavelength fluctuation works as a radiation fluid. For
the long wavelength quantum fluctuation, the effect of back reaction is
equivalent to a negative spatial curvature.Comment: 17 page
Two photon decay of and at finite temperature and density
A comparative study of the anomalous decays , at
finite temperature and at finite density, is performed in the framework of the
three--flavor Nambu--Jona-Lasinio. The similarities and differences between
both scenarios are discussed. In both cases the lifetimes of these mesons
decrease significantly at the critical point, although this might not be
sufficient to observe enhancement of these decays in heavy-ion collisions.Comment: 5 pages, 1 figure. Talk given at Strange Quark Matter 2004, Cape
Town, South Africa, 15-20 September, 200
Solutions of gauge invariant cosmological perturbations in long-wavelength limit
We investigate gauge invariant cosmological perturbations in a spatially flat
Friedman-Robertson-Walker universe with scalar fields. It is well known that
the evolution equation for the gauge invariant quantities has exact solutions
in the long-wavelength limit. We find that these gauge invariant solutions can
be obtained by differentiating the background solution with respect to
parameters contained in the background system. This method is very useful when
we analyze the long-wavelength behavior of cosmological perturbation with
multiple scalar fields.Comment: 17 pages, will appear in Classical and Quantum Gravit
Application of dispersion relations to low-energy meson-nucleon scattering
Relativistic dispersion relations are used to derive equations for low-energy S-, P-, and D-wave meson-nucleon scattering under the assumption that the (3,3) resonance dominates the dispersion integrals. The P-wave equations so obtained differ only slightly from those of the static fixed-source theory. The conclusions of the static theory are re-examined in the light of their new derivation
An Attempt to Construct the Standard Model with Monopoles
We construct a model in which stable magnetic monopoles have magnetic charges
that are identical to the electric charges on leptons and quarks and the
colored monopoles are confined by strings in color singlets.Comment: 10 pages; LaTeX Added clarifying remarks, a Comment on the scattering
of particles, acknowledgements and references. Version to be publishe
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