972 research outputs found
The AdS/CFT Correspondence and a New Positive Energy Conjecture for General Relativity
We examine the AdS/CFT correspondence when the gauge theory is considered on
a compactified space with supersymmetry breaking boundary conditions. We find
that the corresponding supergravity solution has a negative energy, in
agreement with the expected negative Casimir energy in the field theory.
Stability of the gauge theory would imply that this supergravity solution has
minimum energy among all solutions with the same boundary conditions. Hence we
are lead to conjecture a new positive energy theorem for asymptotically locally
Anti-de Sitter spacetimes. We show that the candidate minimum energy solution
is stable against all quadratic fluctuations of the metric.Comment: 25 pages, harvma
Imprints of Short Distance Physics On Inflationary Cosmology
We analyze the impact of certain modifications to short distance physics on
the inflationary perturbation spectrum. For the specific case of power-law
inflation, we find distinctive -- and possibly observable -- effects on the
spectrum of density perturbations.Comment: Revtex 4, 3 eps figs, 4 page
Negative Energy Density in Calabi-Yau Compactifications
We show that a large class of supersymmetric compactifications, including all
simply connected Calabi-Yau and G_2 manifolds, have classical configurations
with negative energy density as seen from four dimensions. In fact, the energy
density can be arbitrarily negative -- it is unbounded from below.
Nevertheless, positive energy theorems show that the total ADM energy remains
positive. Physical consequences of the negative energy density include new
thermal instabilities, and possible violations of cosmic censorship.Comment: 25 pages, v2: few clarifying comments and reference adde
Vacuum Structure of Two-Dimensional Gauge Theories on the Light Front
We discuss the problem of vacuum structure in light-front field theory in the
context of (1+1)-dimensional gauge theories. We begin by reviewing the known
light-front solution of the Schwinger model, highlighting the issues that are
relevant for reproducing the -structure of the vacuum. The most
important of these are the need to introduce degrees of freedom initialized on
two different null planes, the proper incorporation of gauge field zero modes
when periodicity conditions are used to regulate the infrared, and the
importance of carefully regulating singular operator products in a
gauge-invariant way. We then consider SU(2) Yang-Mills theory in 1+1 dimensions
coupled to massless adjoint fermions. With all fields in the adjoint
representation the gauge group is actually SU(2), which possesses
nontrivial topology. In particular, there are two topological sectors and the
physical vacuum state has a structure analogous to a vacuum. We
formulate the model using periodicity conditions in for infrared
regulation, and consider a solution in which the gauge field zero mode is
treated as a constrained operator. We obtain the expected vacuum
structure, and verify that the discrete vacuum angle which enters has no effect
on the spectrum of the theory. We then calculate the chiral condensate, which
is sensitive to the vacuum structure. The result is nonzero, but inversely
proportional to the periodicity length, a situation which is familiar from the
Schwinger model. The origin of this behavior is discussed.Comment: 29 pages, uses RevTeX. Improved discussion of the physical subspace
generally and the vacuum states in particular. Basic conclusions are
unchanged, but some specific results are modifie
Some Remarks on Theories with Large Compact Dimensions and TeV-Scale Quantum Gravity
We comment on some implications of theories with large compactification radii
and TeV-scale quantum gravity. These include the behavior of high-energy
gravitational scattering cross sections and consequences for ultra-high-energy
cosmic rays and neutrino scattering, the question of how to generate naturally
light neutrino masses, the issue of quark-lepton unification, the equivalence
principle, and the cosmological constant.Comment: 28 pages, Late
CD5 expression promotes IL-10 production through activation of the MAPK/Erk pathway and upregulation of TRPC1 channels in B lymphocytes.
CD5 is constitutively expressed on T cells and a subset of mature normal and leukemic B cells in patients with chronic lymphocytic leukemia (CLL). Important functional properties are associated with CD5 expression in B cells, including signal transducer and activator of transcription 3 activation, IL-10 production and the promotion of B-lymphocyte survival and transformation. However, the pathway(s) by which CD5 influences the biology of B cells and its dependence on B-cell receptor (BCR) co-signaling remain unknown. In this study, we show that CD5 expression activates a number of important signaling pathways, including Erk1/2, leading to IL-10 production through a novel pathway independent of BCR engagement. This pathway is dependent on extracellular calcium (Ca2+) entry facilitated by upregulation of the transient receptor potential channel 1 (TRPC1) protein. We also show that Erk1/2 activation in a subgroup of CLL patients is associated with TRPC1 overexpression. In this subgroup of CLL patients, small inhibitory RNA (siRNA) for CD5 reduces TRPC1 expression. Furthermore, siRNAs for CD5 or for TRPC1 inhibit IL-10 production. These findings provide new insights into the role of CD5 in B-cell biology in health and disease and could pave the way for new treatment strategies for patients with B-CLL
(Re)constructing Dimensions
Compactifying a higher-dimensional theory defined in R^{1,3+n} on an
n-dimensional manifold {\cal M} results in a spectrum of four-dimensional
(bosonic) fields with masses m^2_i = \lambda_i, where - \lambda_i are the
eigenvalues of the Laplacian on the compact manifold. The question we address
in this paper is the inverse: given the masses of the Kaluza-Klein fields in
four dimensions, what can we say about the size and shape (i.e. the topology
and the metric) of the compact manifold? We present some examples of
isospectral manifolds (i.e., different manifolds which give rise to the same
Kaluza-Klein mass spectrum). Some of these examples are Ricci-flat, complex and
K\"{a}hler and so they are isospectral backgrounds for string theory. Utilizing
results from finite spectral geometry, we also discuss the accuracy of
reconstructing the properties of the compact manifold (e.g., its dimension,
volume, and curvature etc) from measuring the masses of only a finite number of
Kaluza-Klein modes.Comment: 23 pages, 3 figures, 2 references adde
Application of Pauli-Villars regularization and discretized light-cone quantization to a single-fermion truncation of Yukawa theory
We apply Pauli-Villars regularization and discretized light-cone quantization
to the nonperturbative solution of (3+1)-dimensional Yukawa theory in a
single-fermion truncation. Three heavy scalars, including two with negative
norm, are used to regulate the theory. The matrix eigenvalue problem is solved
for the lowest-mass state with use of a new, indefinite-metric Lanczos
algorithm. Various observables are extracted from the wave functions, including
average multiplicities and average momenta of constituents, structure
functions, and a form factor slope.Comment: 21 pages, 7 figures, RevTeX; published version: more extensive data
in the tables of v
Scaling violations of quark and gluon jet fragmentation functions in e+e- annihilations at sqrt(s) = 91.2 and 183-209 GeV
Flavour inclusive, udsc and b fragmentation functions in unbiased jets, and
flavour inclusive, udsc, b and gluon fragmentation functions in biased jets are
measured in e+e- annihilations from data collected at centre-of-mass energies
of 91.2, and 183-209 GeV with the OPAL detector at LEP. The unbiased jets are
defined by hemispheres of inclusive hadronic events, while the biased jet
measurements are based on three-jet events selected with jet algorithms.
Several methods are employed to extract the fragmentation functions over a wide
range of scales. Possible biases are studied in the results are obtained. The
fragmentation functions are compared to results from lower energy e+e-
experiments and with earlier LEP measurements and are found to be consistent.
Scaling violations are observed and are found to be stronger for the
fragmentation functions of gluon jets than for those of quarks. The measured
fragmentation functions are compared to three recent theoretical
next-to-leading order calculations and to the predictions of three Monte Carlo
event generators. While the Monte Carlo models are in good agreement with the
data, the theoretical predictions fail to describe the full set of results, in
particular the b and gluon jet measurements.Comment: 46 pages, 17 figures, Submitted to Eur. Phys J.
Determination of alpha_s using Jet Rates at LEP with the OPAL detector
Hadronic events produced in e+e- collisions by the LEP collider and recorded
by the OPAL detector were used to form distributions based on the number of
reconstructed jets. The data were collected between 1995 and 2000 and
correspond to energies of 91 GeV, 130-136 GeV and 161-209 GeV. The jet rates
were determined using four different jet-finding algorithms (Cone, JADE, Durham
and Cambridge). The differential two-jet rate and the average jet rate with the
Durham and Cambridge algorithms were used to measure alpha(s) in the LEP energy
range by fitting an expression in which order alpah_2s calculations were
matched to a NLLA prediction and fitted to the data. Combining the measurements
at different centre-of-mass energies, the value of alpha_s (Mz) was determined
to be
alpha(s)(Mz)=0.1177+-0.0006(stat.)+-0.0012$(expt.)+-0.0010(had.)+-0.0032(theo.)
\.Comment: 40 pages, 17 figures, Submitted to Euro. Phys. J.
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