163 research outputs found
Plasma photoemission from string theory
Leading 't Hooft coupling corrections to the photoemission rate of the planar
limit of a strongly-coupled {\cal {N}}=4 SYM plasma are investigated using the
gauge/string duality. We consider the full order \alpha'^3 type IIB string
theory corrections to the supergravity action, including higher order terms
with the Ramond-Ramond five-form field strength. We extend our previous results
presented in arXiv:1110.0526. Photoemission rates depend on the 't Hooft
coupling, and their curves suggest an interpolating behaviour from strong
towards weak coupling regimes. Their slopes at zero light-like momentum give
the electrical conductivity as a function of the 't Hooft coupling, in full
agreement with our previous results of arXiv:1108.6306. Furthermore, we also
study the effect of corrections beyond the large N limit.Comment: 36 pages, 5 figures, paragraph added in the conclusions, references
added, typos correcte
Cosmological Consequences of Nearly Conformal Dynamics at the TeV scale
Nearly conformal dynamics at the TeV scale as motivated by the hierarchy
problem can be characterized by a stage of significant supercooling at the
electroweak epoch. This has important cosmological consequences. In particular,
a common assumption about the history of the universe is that the reheating
temperature is high, at least high enough to assume that TeV-mass particles
were once in thermal equilibrium. However, as we discuss in this paper, this
assumption is not well justified in some models of strong dynamics at the TeV
scale. We then need to reexamine how to achieve baryogenesis in these theories
as well as reconsider how the dark matter abundance is inherited. We argue that
baryonic and dark matter abundances can be explained naturally in these setups
where reheating takes place by bubble collisions at the end of the strongly
first-order phase transition characterizing conformal symmetry breaking, even
if the reheating temperature is below the electroweak scale GeV. We
also discuss inflation as well as gravity wave smoking gun signatures of this
class of models.Comment: 22 pages, 7 figure
A Framework for Fire Safety Management in School Facilities
Schools are high-risk type of facilities in fire emergencies. This requires the implementation of safety measures, which comprise administrative and operational efforts to mitigate the occurrence of fire accidents. The review of literature indicated the lack of practical approaches that can be easily adopted for safety management in school facilities. This paper presents the development and implementation of a generic framework for fire safety management in school facilities. A literature review in the domain of fire safety in schools was performed to comprehend various knowledge areas in this context. A generic framework for fire safety management in school facilities was developed. The framework was implemented in a secondary school, located in the Eastern Province of Saudi Arabia, as a case study, to illustrate its applicability. An action plan was developed to improve the level of fire safety in the school facility, under review. The findings indicated that the framework provides a methodological and systematic approach for assessing the level of fire safety in schools, as well as determine the possible actions for improving the overall safety condition in such facilities. The paper provides a useful focus for practitioners and researchers concerned with fire safety in the educational workplace
On the possibility of light string resonances at the LHC and Tevatron from Randall-Sundrum throats
In string realizations of the Randall-Sundrum scenario, the higher-spin Regge
excitations of Standard Model states localized near the IR brane are warped
down to close to the TeV scale. We argue that, as a consequence of the
localization properties of Randall-Sundrum models of flavour, the lightest such
resonance is the spin-3/2 excitation of the right-handed top quark over a
significant region of parameter space. A mild accidental cancellation allows
this resonance to be as light or lighter than the Kaluza-Klein excitations of
the Standard Model states. We consider from a bottom-up effective theory point
of view the production and possible observability of such a spin-3/2 excitation
at the LHC and Tevatron. Current limits are weaker than might be expected
because of the excess of WWjj events at the Tevatron reported by CDF for an
invariant mass of 400-500 GeV.Comment: 17 pages, 6 figures Version published in JHEP with minor correction
Sequestered Dark Matter
We show that hidden-sector dark matter is a generic feature of the type IIB
string theory landscape and that its lifetime may allow for a discovery through
the observation of very energetic gamma-rays produced in the decay. Throats or,
equivalently, conformally sequestered hidden sectors are common in flux
compactifications and the energy deposited in these sectors can be calculated
if the reheating temperature of the standard model sector is known. Assuming
that throats with various warp factors are available in the compact manifold,
we determine which throats maximize the late-time abundance of sequestered dark
matter. For such throats, this abundance agrees with cosmological data if the
standard model reheating temperature was 10^10 - 10^11 GeV. In two distinct
scenarios, the mass of dark matter particles, i.e. the IR scale of the throat,
is either around 10^5 GeV or around 10^10 GeV. The lifetime and the decay
channels of our dark matter candidates depend crucially on the fact that the
Klebanov-Strassler throat is supersymmetric. Furthermore, the details of
supersymmetry breaking both in the throat and in the visible sector play an
essential role. We identify a number of scenarios where this type of dark
matter can be discovered via gamma-ray observations.Comment: 36 pages, 3 figures; v2: references added, v3: introduction extended
and typos correcte
String Phenomenology at the LHC
We consider extensions of the standard model based on open strings ending on
D-branes, with gauge bosons due to strings attached to stacks of D-branes and
chiral matter due to strings stretching between intersecting D-branes. Assuming
that the fundamental string mass scale is in the TeV range and the theory is
weakly coupled, we review possible signals of string physics at the Large
Hadron Collider.Comment: 10 pages, 3 eps figures. Solicited Brief Review prepared for Modern
Physics Letters A; typographical error in equations (8), (9), (10), and (11)
has been correcte
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