835 research outputs found
Optimization of plasmonâplasmon coupling in photorefractive layered media
In this paper we study grating-induced plasmonâplasmon coupling in photorefractive layered media using a weakcoupling approximation. The method used is applicable to general layered structures that support both plasmonic and optical modes, such as photorefractive liquid crystal cells. The approximate equations are accurate when compared to S matrix approaches and capture the plasmon propagation at the surface of the device along with the optical modes guided by the layered geometry underneath. Analysis of the resulting model provides insight into the effect of the control parameters in this device and the means to optimize the diffraction efficiency. For example, by considering the case in which the plasmon is spectrally separated from the guided modes it is possible to determine the optimum gold thickness and grating strength required to obtain the strongest possible diffraction
Observation of a kilogram-scale oscillator near its quantum ground state
We introduce a novel cooling technique capable of approaching the quantum ground state of a kilogram-scale system-an interferometric gravitational wave detector. The detectors of the Laser Interferometer Gravitational-wave Observatory (LIGO) operate within a factor of 10 of the standard quantum limit (SQL), providing a displacement sensitivity of 10â18 m in a 100 Hz band centered on 150 Hz. With a new feedback strategy, we dynamically shift the resonant frequency of a 2.7 kg pendulum mode to lie within this optimal band, where its effective temperature falls as low as 1.4 ÎŒK, and its occupation number reaches about 200 quanta. This work shows how the exquisite sensitivity necessary to detect gravitational waves can be made available to probe the validity of quantum mechanics on an enormous mass scale
The Fall of Stringy de Sitter
Kachru, Kallosh, Linde, & Trivedi recently constructed a four-dimensional de
Sitter compactification of IIB string theory, which they showed to be
metastable in agreement with general arguments about de Sitter spacetimes in
quantum gravity. In this paper, we describe how discrete flux choices lead to a
closely-spaced set of vacua and explore various decay channels. We find that in
many situations NS5-brane meditated decays which exchange NSNS 3-form flux for
D3-branes are comparatively very fast.Comment: 35 pp (11 pp appendices), 5 figures, v3. fixed minor typo
Black Hole Chromosphere at the LHC
If the scale of quantum gravity is near a TeV, black holes will be copiously
produced at the LHC. In this work we study the main properties of the light
descendants of these black holes. We show that the emitted partons are closely
spaced outside the horizon, and hence they do not fragment into hadrons in
vacuum but more likely into a kind of quark-gluon plasma. Consequently, the
thermal emission occurs far from the horizon, at a temperature characteristic
of the QCD scale. We analyze the energy spectrum of the particles emerging from
the "chromosphere", and find that the hard hadronic jets are almost entirely
suppressed. They are replaced by an isotropic distribution of soft photons and
hadrons, with hundreds of particles in the GeV range. This provides a new
distinctive signature for black hole events at LHC.Comment: Incorporates changes made for the version to be published in Phys.
Rev. D. Additional details provided on the effect of the chromosphere in
cosmic ray shower
Phenomenology of Randall-Sundrum Black Holes
We explore the phenomenology of microscopic black holes in the
Randall-Sundrum (RS) model. We consider the canonical framework in which both
gauge and matter fields are confined to the brane and only gravity spills into
the extra dimension. The model is characterized by two parameters, the mass of
the first massive graviton , and the curvature of the RS
anti-de Sitter space. We compute the sensitivity of present and future cosmic
ray experiments to various regions of and and compare with that
of Runs I and II at the Tevatron. As part of our phenomenological analysis, we
examine constraints placed on by AdS/CFT considerations.Comment: Version to appear in Physical Review D; contains additional analysis
on sensitivity of OW
Constraints on Cosmic Strings from the LIGO-Virgo Gravitational-Wave Detectors
Cosmic strings can give rise to a large variety of interesting astrophysical phenomena. Among them, powerful bursts of gravitational waves (GWs) produced by cusps are a promising observational signature. In this Letter we present a search for GWs from cosmic string cusps in data collected by the LIGO and Virgo gravitational wave detectors between 2005 and 2010, with over 625 days of live time. We find no evidence of GW signals from cosmic strings. From this result, we derive new constraints on cosmic string parameters, which complement and improve existing limits from previous searches for a stochastic background of GWs from cosmic microwave background measurements and pulsar timing data. In particular, if the size of loops is given by the gravitational backreaction scale, we place upper limits on the string tension (Newton's Constant x mass per unit length) below 10(exp 8) in some regions of the cosmic string parameter space
Renormalization Group Flow of Quantum Gravity in the Einstein-Hilbert Truncation
The exact renormalization group equation for pure quantum gravity is used to
derive the non-perturbative \Fbeta-functions for the dimensionless Newton
constant and cosmological constant on the theory space spanned by the
Einstein-Hilbert truncation. The resulting coupled differential equations are
evaluated for a sharp cutoff function. The features of these flow equations are
compared to those found when using a smooth cutoff. The system of equations
with sharp cutoff is then solved numerically, deriving the complete
renormalization group flow of the Einstein-Hilbert truncation in . The
resulting renormalization group trajectories are classified and their physical
relevance is discussed. The non-trivial fixed point which, if present in the
exact theory, might render Quantum Einstein Gravity nonperturbatively
renormalizable is investigated for various spacetime dimensionalities.Comment: 58 pages, latex, 24 figure
Detecting Microscopic Black Holes with Neutrino Telescopes
If spacetime has more than four dimensions, ultra-high energy cosmic rays may
create microscopic black holes. Black holes created by cosmic neutrinos in the
Earth will evaporate, and the resulting hadronic showers, muons, and taus may
be detected in neutrino telescopes below the Earth's surface. We simulate such
events in detail and consider black hole cross sections with and without an
exponential suppression factor. We find observable rates in both cases: for
conservative cosmogenic neutrino fluxes, several black hole events per year are
observable at the IceCube detector; for fluxes at the Waxman-Bahcall bound,
tens of events per year are possible. We also present zenith angle and energy
distributions for all three channels. The ability of neutrino telescopes to
differentiate hadrons, muons, and possibly taus, and to measure these
distributions provides a unique opportunity to identify black holes, to
experimentally constrain the form of black hole production cross sections, and
to study Hawking evaporation.Comment: 20 pages, 9 figure
Black Holes from Cosmic Rays: Probes of Extra Dimensions and New Limits on TeV-Scale Gravity
If extra spacetime dimensions and low-scale gravity exist, black holes will
be produced in observable collisions of elementary particles. For the next
several years, ultra-high energy cosmic rays provide the most promising window
on this phenomenon. In particular, cosmic neutrinos can produce black holes
deep in the Earth's atmosphere, leading to quasi-horizontal giant air showers.
We determine the sensitivity of cosmic ray detectors to black hole production
and compare the results to other probes of extra dimensions. With n \ge 4 extra
dimensions, current bounds on deeply penetrating showers from AGASA already
provide the most stringent bound on low-scale gravity, requiring a fundamental
Planck scale M_D > 1.3 - 1.8 TeV. The Auger Observatory will probe M_D as large
as 4 TeV and may observe on the order of a hundred black holes in 5 years. We
also consider the implications of angular momentum and possible exponentially
suppressed parton cross sections; including these effects, large black hole
rates are still possible. Finally, we demonstrate that even if only a few black
hole events are observed, a standard model interpretation may be excluded by
comparison with Earth-skimming neutrino rates.Comment: 30 pages, 18 figures; v2: discussion of gravitational infall, AGASA
and Fly's Eye comparison added; v3: Earth-skimming results modified and
strengthened, published versio
Experimental Probes of Localized Gravity: On and Off the Wall
The phenomenology of the Randall-Sundrum model of localized gravity is
analyzed in detail for the two scenarios where the Standard Model (SM) gauge
and matter fields are either confined to a TeV scale 3-brane or may propagate
in a slice of five dimensional anti-deSitter space. In the latter instance, we
derive the interactions of the graviton, gauge, and fermion Kaluza-Klein (KK)
states. The resulting phenomenological signatures are shown to be highly
dependent on the value of the 5-dimensional fermion mass and differ
substantially from the case where the SM fields lie on the TeV-brane. In both
scenarios, we examine the collider signatures for direct production of the
graviton and gauge KK towers as well as their induced contributions to
precision electroweak observables. These direct and indirect signatures are
found to play a complementary role in the exploration of the model parameter
space. In the case where the SM field content resides on the TeV-brane, we show
that the LHC can probe the full parameter space and hence will either discover
or exclude this model if the scale of electroweak physics on the 3-brane is
less than 10 TeV. We also show that spontaneous electroweak symmetry breaking
of the SM must take place on the TeV-brane.Comment: 62 pages, Latex, 22 figure
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