179 research outputs found
Super Heavy Dark Matter Anisotropies from D-particles in the Early Universe
We discuss a way of producing anisotropies in the spectrum of superheavy Dark
matter, which are due to the distortion of the inflationary space time induced
by the recoil of D-particles upon their scattering with ordinary string matter
in the Early Universe. We calculate such distortions by world-sheet Liouville
string theory (perturbative) methods. The resulting anisotropies are found to
be proportional to the average recoil velocity and density of the D-particles.
In our analysis we employ a regulated version of de Sitter space, allowing for
graceful exit from inflation. This guarantees the asymptotic flatness of the
space time, as required for a consistent interpretation, within an effective
field theory context, of the associated Bogolubov coefficients as particle
number densities. The latter are computed by standard WKB methods.Comment: 30 pages Latex, two eps figures incorporate
Vacuum thin shell solutions in five-dimensional Lovelock gravity
Junction conditions for vacuum solutions in five-dimensional
Einstein-Gauss-Bonnet gravity are studied. We focus on those cases where two
spherically symmetric regions of space-time are joined in such a way that the
induced stress tensor on the junction surface vanishes. So a spherical vacuum
shell, containing no matter, arises as a boundary between two regions of the
space-time. Such solutions are a generalized kind of spherically symmetric
empty space solutions, described by metric functions of the class . New
global structures arise with surprising features. In particular, we show that
vacuum spherically symmetric wormholes do exist in this theory. These can be
regarded as gravitational solitons, which connect two asymptotically (Anti)
de-Sitter spaces with different masses and/or different effective cosmological
constants. We prove the existence of both static and dynamical solutions and
discuss their (in)stability under perturbations that preserve the symmetry.
This leads us to discuss a new type of instability that arises in
five-dimensional Lovelock theory of gravity for certain values of the coupling
of the Gauss-Bonnet term.Comment: 9 pages. This is an extended version of the authors' contribution to
the Proceedings of the Marcel Grossmann Meeting, held in Paris, 12-18 July
200
Impact of Low-Energy Constraints on Lorentz Violation
We extend previous analyses of the violation of Lorentz invariance induced in
a non-critical string model of quantum space-time foam, discussing the
propagation of low-energy particles through a distribution of non-relativistic
D-particles.We argue that nuclear and atomic physics experiments do not
constitute sensitive probes of this approach to quantum gravity due to a
difference in the dispersion relations for massive probes as compared to those
for massless ones, predicted by the model.Comment: 4 pages revte
`Mass without mass' from thin shells in Gauss-Bonnet gravity
Five tensor equations are obtained for a thin shell in Gauss-Bonnet gravity.
There is the well known junction condition for the singular part of the stress
tensor intrinsic to the shell, which we also prove to be well defined. There
are also equations relating the geometry of the shell (jump and average of the
extrinsic curvature as well as the intrinsic curvature) to the non-singular
components of the bulk stress tensor on the sides of the thin shell.
The equations are applied to spherically symmetric thin shells in vacuum. The
shells are part of the vacuum, they carry no energy tensor. We classify these
solutions of `thin shells of nothingness' in the pure Gauss-Bonnet theory.
There are three types of solutions, with one, zero or two asymptotic regions
respectively. The third kind of solution are wormholes. Although vacuum
solutions, they have the appearance of mass in the asymptotic regions. It is
striking that in this theory, exotic matter is not needed in order for
wormholes to exist- they can exist even with no matter.Comment: 13 pages, RevTex, 8 figures. Version 2: includes discussion on the
well-defined thin shell limit. Version 3: typos fixed, a reference added,
accepted for publication in Phys. Rev.
Shock waves and Birkhoff's theorem in Lovelock gravity
Spherically symmetric shock waves are shown to exist in Lovelock gravity.
They amount to a change of branch of the spherically symmetric solutions across
a null hypersurface. The implications of their existence for the status of
Birkhoff's theorem in the theory is discussed.Comment: 9 pages, no figures, clarifying changes made in the text of section
III and references adde
Phase transitions in general gravity theories
Phase transitions between two competing vacua of a given theory are quite
common in physics. We discuss how to construct the space-time solutions that
allow the description of phase transitions between different branches (or
asymptotics) of a given higher curvature gravity theory at finite temperature.Comment: 4 pages, 1 figure, Contribution to the Conference Proceedings of the
Spanish Relativity Meeting in Portugal (ERE2012
Generalized Batchelor functions of isotropic turbulence
We generalize Batchelor's parameterization of the autocorrelation functions
of isotropic turbulence in a form involving a product expansion with multiple
small scales. The richer small scale structure acquired this way, compared to
the usual Batchelor function, is necessary so that the associated energy
spectrum approximate well actual spectra in the universal equilibrium range. We
propose that the generalized function provides an approximation of arbitrary
accuracy for actual spectra of isotropic turbulence over the universal
equilibrium range. The degree of accuracy depends on the number of higher
moments which are determinable and it is reflected in the number of small
scales involved. The energy spectrum of the generalized function is derived,
and for the case of two small scales is compared with data from high-resolution
direct numerical simulations. We show that the compensated spectra (which
illustrate the bottleneck effect) and dissipation spectra are encapsulated
excellently, in accordance with our proposal
- …