652 research outputs found
Reply to the "Comment on: Detecting Vanishing Dimensions Via Primordial Gravitational Wave Astronomy"
The "Comment on: Detecting Vanishing Dimensions Via Primordial Gravitational
Wave Astronomy" [arXiv:1104.1223] is misleading and premised on a
misinterpretation of the main content of Phys. Rev. Lett. 106, 101101 (2011)
[arXiv:1102.3434]. The main claim in the comment - that in some exotic theories
different from general relativity (GR) there might be local degrees of freedom
even in lower dimensional spaces - is trivial. Nevertheless, the authors of the
Comment fail to come-up with a single self-consistent example. This claim,
however, has no implications for our paper, in which we make it clear we are
working within the framework of "vanishing" or "evolving" dimensions as defined
in arXiv:1003.5914.Comment: Accepted for publication in Phys. Rev. Let
Hawking radiation of unparticles
Unparticle degrees of freedom, no matter how weakly coupled to the standard
model particles, must affect the evolution of a black hole, which thermally
decays into all available degrees of freedom. We develop a method for
calculating the grey-body factors for scalar unparticles for 3+1 and higher
dimensional black holes. We find that the power emitted in unparticles may be
quite different from the power emitted in ordinary particles. Depending on the
parameters in the model, unparticles may become the dominant channel. This is
of special interest for small primordial black holes and also in models with
low scale quantum gravity where the experimental signature may significantly be
affected. We also discuss the sensitivity of the results on the (currently
unknown) unparticle normalization.Comment: Calculations for different normalization of unparticles included,
discussion expanded, version published in Phys. Rev.
Energy flux through the horizon in the black hole-domain wall systems
We study various configurations in which a domain wall (or cosmic string),
described by the Nambu-Goto action, is embedded in a background space-time of a
black hole in and higher dimensional models. We calculate energy fluxes
through the black hole horizon. In the simplest case, when a static domain wall
enters the horizon of a static black hole perperdicularly, the energy flux is
zero. In more complicated situations, where parameters which describe the
domain wall surface are time and position dependent, the flux is non-vanishing
is principle. These results are of importance in various conventional
cosmological models which accommodate the existence of domain walls and strings
and also in brane world scenarios.Comment: references added, accepted for publication in JHE
Detecting Vanishing Dimensions Via Primordial Gravitational Wave Astronomy
Lower-dimensionality at higher energies has manifold theoretical advantages
as recently pointed out. Moreover, it appears that experimental evidence may
already exists for it - a statistically significant planar alignment of events
with energies higher than TeV has been observed in some earlier cosmic ray
experiments. We propose a robust and independent test for this new paradigm.
Since (2+1)-dimensional spacetimes have no gravitational degrees of freedom,
gravity waves cannot be produced in that epoch. This places a universal maximum
frequency at which primordial waves can propagate, marked by the transition
between dimensions. We show that this cut-off frequency may be accessible to
future gravitational wave detectors such as LISA.Comment: Somewhat expanded version with discussions that could not fit into
the PRL version; references adde
Fermionic Zero Modes on Domain Walls
We study fermionic zero modes in the domain wall background. The fermions
have Dirac and left- and right-handed Majorana mass terms. The source of the
Dirac mass term is the coupling to a scalar field . The source of the
Majorana mass terms could also be the coupling to a scalar field or a
vacuum expectation value of some other field acquired in a phase transition
well above the phase transition of the field . We derive the fermionic
equations of motion and find the necessary and sufficient conditions for a zero
mode to exist. We also find the solutions numerically. In the absence of the
Majorana mass terms, the equations are solvable analytically. In the case of
massless fermions a zero energy solution exists and we show that although this
mode is not discretely normalizable it is Dirac delta function normalizable and
should be viewed as part of a continuum spectrum rather than as an isolated
zero mode.Comment: 6 pages, 3 figures, matches version published in PR
A black hole solution to the cosmological monopole problem
We propose a solution to the cosmological monopole problem: Primordial black
holes, produced in the early universe, can accrete magnetic monopoles before
the relics dominate the energy density of the universe. These small black holes
quickly evaporate and thereby convert most of the monopole energy density into
radiation. We estimate the range of parameters for which this solution is
possible: under very conservative assumptions we find that the black hole mass
must be less than 10^9 gm.Comment: accepted for publication in Phys. Lett.
Non-Universal Power Law of the "Hall Scattering Rate" in a Single-Layer Cuprate Bi_{2}Sr_{2-x}La_{x}CuO_{6}
In-plane resistivity \rho_{ab}, Hall coefficient, and magnetoresistance (MR)
are measured in a series of high-quality Bi_{2}Sr_{2-x}La_{x}CuO_{6} crystals
with various carrier concentrations, from underdope to overdope. Our crystals
show the highest T_c (33 K) and the smallest residual resistivity ever reported
for Bi-2201 at optimum doping. It is found that the temperature dependence of
the Hall angle obeys a power law T^n with n systematically decreasing with
increasing doping, which questions the universality of the Fermi-liquid-like
T^2 dependence of the "Hall scattering rate". In particular, the Hall angle of
the optimally-doped sample changes as T^{1.7}, not as T^2, while \rho_{ab}
shows a good T-linear behavior. The systematics of the MR indicates an
increasing role of spin scattering in underdoped samples.Comment: 4 pages, 5 figure
Effect of FET geometry on charge ordering of transition metal oxides
We examine the effect of an FET geometry on the charge ordering phase diagram
of transition metal oxides using numerical simulations of a semiclassical model
including long-range Coulomb fields, resulting in nanoscale pattern formation.
We find that the phase diagram is unchanged for insulating layers thicker than
approximately twice the magnetic correlation length. For very thin insulating
layers, the onset of a charge clump phase is shifted to lower values of the
strength of the magnetic dipolar interaction, and intermediate diagonal stripe
and geometric phases can be suppressed. Our results indicate that, for
sufficiently thick insulating layers, charge injection in an FET geometry can
be used to experimentally probe the intrinsic charge ordering phases in these
materials.Comment: 4 pages, 4 postscript figure
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