6,473 research outputs found
Searching for Gravitational Waves from Binary Inspirals with LIGO
We describe the current status of the search for gravitational waves from
inspiralling compact binary systems in LIGO data. We review the result from the
first scientific run of LIGO (S1). We present the goals of the search of data
taken in the second scientific run (S2) and describe the differences between
the methods used in S1 and S2.Comment: 9 pages, 2 figures. Published in proceedings of the 8th Gravitational
Wave Data Analysis Workshop, Milwaukee, WI, USA, 17-20 December 200
Negative Energy in String Theory and Cosmic Censorship Violation
We find asymptotically anti de Sitter solutions in N=8 supergravity which
have negative total energy. This is possible since the boundary conditions
required for the positive energy theorem are stronger than those required for
finite mass (and allowed by string theory). But stability of the anti de Sitter
vacuum is still ensured by the positivity of a modified energy, which includes
an extra surface term. Some of the negative energy solutions describe classical
evolution of nonsingular initial data to naked singularities. Since there is an
open set of such solutions, cosmic censorship is violated generically in
supergravity. Using the dual field theory description, we argue that these
naked singularities will be resolved in the full string theory.Comment: 23 pages, 2 figures, v2: argument for forming naked singularities
clarified, references adde
Cosmic Strings and Superstrings
Cosmic strings are predicted by many field-theory models, and may have been
formed at a symmetry-breaking transition early in the history of the universe,
such as that associated with grand unification. They could have important
cosmological effects. Scenarios suggested by fundamental string theory or
M-theory, in particular the popular idea of brane inflation, also strongly
suggest the appearance of similar structures. Here we review the reasons for
postulating the existence of cosmic strings or superstrings, the various
possible ways in which they might be detected observationally, and the special
features that might discriminate between ordinary cosmic strings and
superstrings.Comment: Minor errors corrected and some references added, 34 pages, 6 figure
Bounds on Universal Extra Dimensions
We show that the bound from the electroweak data on the size of extra
dimensions accessible to all the standard model fields is rather loose. These
"universal" extra dimensions could have a compactification scale as low as 300
GeV for one extra dimension. This is because the Kaluza-Klein number is
conserved and thus the contributions to the electroweak observables arise only
from loops. The main constraint comes from weak-isospin violation effects. We
also compute the contributions to the S parameter and the vertex.
The direct bound on the compactification scale is set by CDF and D0 in the few
hundred GeV range, and the Run II of the Tevatron will either discover extra
dimensions or else it could significantly raise the bound on the
compactification scale. In the case of two universal extra dimensions, the
current lower bound on the compactification scale depends logarithmically on
the ultra-violet cutoff of the higher dimensional theory, but can be estimated
to lie between 400 and 800 GeV. With three or more extra dimensions, the cutoff
dependence may be too strong to allow an estimate.Comment: 22 pages, Latex, 1 eps figure. Published version; minor correction in
the Kaluza-Klein decompositio
Semi-Inclusive Lambda and Kshort Production in p-Au Collisions at 17.5 GeV/c
The first detailed measurements of the centrality dependence of strangeness
production in p-A collisions are presented. Lambda and Kshort dn/dy
distributions from 17.5 GeV/c p-Au collisions are shown as a function of "grey"
track multiplicity and the estimated number of collisions, nu, made by the
proton. The nu dependence of the Lambda yield deviates from a scaling of p-p
data by the number of participants, increasing faster than this scaling for
nu<=5 and saturating for larger nu. A slower growth in Kshort multiplicity with
nu is observed, consistent with a weaker nu dependence of K-Kbar production
than Y-K production.Comment: 5 pages, 3 figures, formatted with RevTex, current version has
enlarged figure catpion
B Production Asymmetries in Perturbative QCD
This paper explores a new mechanism for B production in which a b quark
combines with a light parton from the hard-scattering process before
hadronizing into the B hadron. This recombination mechanism can be calculated
within perturbative QCD up to a few nonperturbative constants. Though
suppressed at large transverse momentum by a factor Lambda_QCD m_b/p_t^2
relative to b quark fragmentation production, it can be important at large
rapidities. A signature for this heavy-quark recombination mechanism in
proton-antiproton colliders is the presence of rapidity asymmetries in B cross
sections. Given reasonable assumptions about the size of nonperturbative
parameters entering the calculation, we find that the asymmetries are only
significant for rapidities larger than those currently probed by collider
experiments.Comment: 17 pages, LaTeX, 4 ps figures, tightenlines, sections added, final
version accepted for publication in Phys. Rev.
Don't Stop Thinking About Leptoquarks: Constructing New Models
We discuss the general framework for the construction of new models
containing a single, fermion number zero scalar leptoquark of mass GeV which can both satisfy the D0/CDF search constraints as well as
low energy data, and can lead to both neutral and charged current-like final
states at HERA. The class of models of this kind necessarily contain new
vector-like fermions with masses at the TeV scale which mix with those of the
Standard Model after symmetry breaking. In this paper we classify all models of
this type and examine their phenomenological implications as well as their
potential embedding into SUSY and non-SUSY GUT scenarios. The general coupling
parameter space allowed by low energy as well as collider data for these models
is described and requires no fine-tuning of the parameters.Comment: Modified text, added table, and updated reference
Cardiorespiratory fitness is associated with hard and light intensity physical activity but not time spent sedentary in 10–14 year old schoolchildren: the HAPPY study
Sedentary behaviour is a major risk factor for developing chronic diseases and is associated with low cardiorespiratory fitness in adults. It remains unclear how sedentary behaviour and different physical activity subcomponents are related to cardiorespiratory fitness in children. The purpose of this study was to assess how sedentary behaviour and different physical activity subcomponents are associated with 10–14 year-old schoolchildren's cardiorespiratory fitness
Functional Genomic and Proteomic Analysis Reveals Disruption of Myelin-Related Genes and Translation in a Mouse Model of Early Life Neglect
Early life neglect is an important public health problem which can lead to lasting psychological dysfunction. Good animal models are necessary to understand the mechanisms responsible for the behavioral and anatomical pathology that results. We recently described a novel model of early life neglect, maternal separation with early weaning (MSEW), that produces behavioral changes in the mouse that persist into adulthood. To begin to understand the mechanism by which MSEW leads to these changes we applied cDNA microarray, next-generation RNA-sequencing (RNA-seq), label-free proteomics, multiple reaction monitoring (MRM) proteomics, and methylation analysis to tissue samples obtained from medial prefrontal cortex to determine the molecular changes induced by MSEW that persist into adulthood. The results show that MSEW leads to dysregulation of markers of mature oligodendrocytes and genes involved in protein translation and other categories, an apparent downward biasing of translation, and methylation changes in the promoter regions of selected dysregulated genes. These findings are likely to prove useful in understanding the mechanism by which early life neglect affects brain structure, cognition, and behavior
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