720 research outputs found
Regularisation of classical self interaction in strings
A general method of regularisation of classical self interaction in strings
is extended from the electromagnetic case (for which it was originally
developed) to the gravitation case, for which the result can also be
represented as a renormalisation.Comment: 4 pages, Latex. Contribution to proceedings of 1997 Cargese A.S.I.
``Strings, branes, and dualities'', ed. L. Baulieu, P. Winde
f(R) as a dark energy fluid
We study the equations for the evolution of cosmological perturbations in
and conclude that this modified gravity model can
be expressed as a dark energy fluid at background and linearised perturbation
order. By eliminating the extra scalar degree of freedom known to be present in
such theories, we are able to characterise the evolution of the perturbations
in the scalar sector in terms of equations of state for the entropy
perturbation and anisotropic stress which are written in terms of the density
and velocity perturbations of the dark energy fluid and those in the matter, or
the metric perturbations. We also do the same in the much simpler vector and
tensor sectors. In order to illustrate the simplicity of this formulation, we
numerically evolve perturbations in a small number of cases.Comment: 12 pages, 5 figure
Rigidity and stability of cold dark solid universe model
Observational evidence suggests that the large scale dynamics of the universe
is presently dominated by dark energy, meaning a non-luminous cosmological
constituent with a negative value of the pressure to density ratio ,
which would be unstable if purely fluid, but could be stable if effectively
solid with sufficient rigidity. It was suggested by Bucher and Spergel that
such a solid constituent might be constituted by an effectively cold (meaning
approximately static) distribution of cosmic strings with , or
membranes with the observationally more favoured value , but it was not
established whether the rigidity in such models actually would be sufficient
for stabilisation. The present article provides an explicit evaluation of the
rigidity to density ratio, which is shown to be given in both string and
membrane cases by , and it is confirmed that this is indeed
sufficient for stabilisation.Comment: 6 pages latex, revised version extended to include 4 figure
Scaling Dynamics of Domain Walls in the Cubic Anisotropy Model
We have investigated the dynamics of domain walls in the cubic anisotropy
model. In this model a global O(N) symmetry is broken to a set of discrete
vacua either on the faces, or vertices of a (hyper)cube. We compute the scaling
exponents for in two dimensions on grids of points and
compare them to the fiducial model of symmetry breaking. Since the model
allows for wall junctions lattice structures are locally stable and
modifications to the standard scaling law are possible. However, we find that
since there is no scale which sets the distance between walls, the walls appear
to evolve toward a self-similar regime with .Comment: 16 pages, 12 figure
Poly-essential and general Hyperelastic World (brane) models
This article provides a unified treatment of an extensive category of
non-linear classical field models whereby the universe is represented (perhaps
as a brane in a higher dimensional background) in terms of a structure of a
mathematically convenient type describable as hyperelastic, for which a
complete set of equations of motion is provided just by the energy-momentum
conservation law. Particular cases include those of a perfect fluid in
quintessential backgrounds of various kinds, as well as models of the elastic
solid kind that has been proposed to account for cosmic acceleration. It is
shown how an appropriately generalised Hadamard operator can be used to
construct a symplectic structure that controles the evolution of small
perturbations, and that provides a characteristic equation governing the
propagation of weak discontinuities of diverse (extrinsic and extrinsic) kinds.
The special case of a poly-essential model - the k-essential analogue of an
ordinary polytropic fluid - is examined and shown to be well behaved (like the
fluid) only if the pressure to density ratio is positive.Comment: 16 pages Latex, Contrib. to 10th Peyresq Pysics Meeting, June 2005:
Micro and Macro Structures of Spacetim
Generic junction conditions in brane-world scenarios
We present the generic junction conditions obeyed by a co-dimension one brane in an arbitrary background spacetime. As well as the usual Darmois-Israel junction conditions which relate the discontinuity in the extrinsic curvature to the to the energy-momentum tensor of matter which is localized to the brane, we point out that another condition must also be obeyed. This condition, which is the analogous to Newton's second law for a point particle, is trivially satisfied when symmetry is enforced by hand, but in more general circumstances governs the evolution of the brane world-volume. As an illustration of its effect we compute the force on the brane due to a form field
Cold Compressed Baryonic Matter with Hidden Local Symmetry and Holography
I describe a novel phase structure of cold dense baryonic matter predicted in
a hidden local symmetry approach anchored on gauge theory and in a holographic
dual approach based on the Sakai-Sugimoto model of string theory. This new
phase is populated with baryons with half-instanton quantum number in the
gravity sector which is dual to half-skyrmion in gauge sector in which chiral
symmetry is restored while light-quark hadrons are in the color-confined phase.
It is suggested that such a phase that aries at a density above that of normal
nuclear matter and below or at the chiral restoration point can have a drastic
influence on the properties of hadrons at high density, in particular on
short-distance interactions between nucleons, e.g., multi-body forces at short
distance and hadrons -- in particular kaons -- propagating in a dense medium.
Potentially important consequences on the structure of compact stars will be
predicted.Comment: 15 pages, to appear in proceedings of "Strong Coupling Gauge Theories
in LHC Era (SCGT09)," Nagoya, Japa
Hybrid Inflation Exit through Tunneling
For hybrid inflationary potentials, we derive the tunneling rate from field
configurations along the flat direction towards the waterfall regime. This
process competes with the classically rolling evolution of the scalar fields
and needs to be strongly subdominant for phenomenologically viable models.
Tunneling may exclude models with a mass scale below 10^12 GeV, but can be
suppressed by small values of the coupling constants. We find that tunneling is
negligible for those models, which do not require fine tuning in order to
cancel radiative corrections, in particular for GUT-scale SUSY inflation. In
contrast, electroweak scale hybrid inflation is not viable, unless the
inflaton-waterfall field coupling is smaller than approximately 10^-11.Comment: 17 pages, 2 figure
Strange and Heavy Flavoured Hypernuclei in Chiral Soliton Models
The extention of the chiral soliton approach to hypernuclei - strange or
heavy flavoured - becomes more reliable due to success in describing of other
properties of nuclei, e.g. the symmetry energy of nuclei with atomic numbers up
to ~30. The binding energies of the ground states of light hypernuclei with
strangeness S=-1 have been described in qualitative agreement with data. The
existence of charmed or beautiful hypernuclei and Theta-hypernuclei (strange,
charmed or beautiful) with large binding energy is expected within same
approach.Comment: 5 pages, 4 figures. Talk given at the 9-th International Conference
on Hypernuclei and Strange Particle Physics (HYP2006), Mainz, Germany, 10-14
October 2006. Extended version "Baryon States in Chiral Soliton Models; from
Nuclei to Exotic Baryons" presented at the International Workshop "High
Energy Physics in the LHC Era", Universidad Tecnica Federico Santa Maria,
Valparaiso, Chile, 11-15 December 200
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