1,088 research outputs found
Noncommutative Super Yang-Mills Theories with 8 Supercharges and Brane Configurations
In this paper we consider D=4 NCSYM theories with 8 supercharges. We study
these theories through a proper type IIA (and M-theory) brane configuration. We
find the one loop beta function of these theories and show that there is an
elliptic curve describing the moduli space of the theory, which is in principle
the same as the curve for the commutative counter-part of our theory. We study
some other details of the dynamics by means of this brane configuration.Comment: 14 pages, no figures, v2: typos correcte
On Measuring Split-SUSY Neutralino and Chargino Masses at the LHC
In Split-Supersymmetry models, where the only non-Standard Model states
produceable at LHC-energies consist of a gluino plus neutralinos and charginos,
it is conventionally accepted that only mass differences among these latter are
measureable at the LHC. The present work shows that application of a simple
`Kinematic Selection' technique allows full reconstruction of neutralino and
chargino masses from one event, in principle. A Monte Carlo simulation
demonstrates the feasibilty of using this technique at the LHC.Comment: 17 pages, 4 figures; EPJC versio
Noncommutative SO(n) and Sp(n) Gauge Theories
We study the generalization of noncommutative gauge theories to the case of
orthogonal and symplectic groups. We find out that this is possible, since we
are allowed to define orthogonal and symplectic subgroups of noncommutative
unitary gauge transformations even though the gauge potentials and gauge
transformations are not valued in the orthogonal and symplectic subalgebras of
the Lie algebra of antihermitean matrices. Our construction relies on an
antiautomorphism of the basic noncommutative algebra of functions which
generalizes the charge conjugation operator of ordinary field theory. We show
that the corresponding noncommutative picture from low energy string theory is
obtained via orientifold projection in the presence of a non-trivial NSNS
B-field.Comment: 17 pages; considerations about fermions added and some minor change
Final State Interactions in Hypernuclear Decay
We present an update of the One-Meson-Exchange (OME) results for the weak
decay of s- and p-shell hypernuclei (Ref. Phys. Rev. C {\bf 56}, 339 (1997)),
paying special attention to the role played by final state interactions between
the emitted nucleons. The present study also corrects for a mistake in the
inclusion of the and exchange mechanisms, which substantially
increases the ratio of neutron-induced to proton-induced transitions,
. With the most up-to-date model ingredients, we find that
the OME approach is able to describe very satisfactorily most of the measured
observables, including the ratio .Comment: 20 pages, 2 eps figure
Dirac Quantization of Open Strings and Noncommutativity in Branes
We apply the Dirac bracket quantization to open strings attached to branes in
the presence of background antisymmetric field and recover an inherent
noncommutativity in the internal coordinates of the brane.Comment: 25 pp, typos corrected, minor change
Weak Field Black Hole Formation in Asymptotically AdS Spacetimes
We use the AdS/CFT correspondence to study the thermalization of a strongly
coupled conformal field theory that is forced out of its vacuum by a source
that couples to a marginal operator. The source is taken to be of small
amplitude and finite duration, but is otherwise an arbitrary function of time.
When the field theory lives on , the source sets up a
translationally invariant wave in the dual gravitational description. This wave
propagates radially inwards in space and collapses to form a black
brane. Outside its horizon the bulk spacetime for this collapse process may
systematically be constructed in an expansion in the amplitude of the source
function, and takes the Vaidya form at leading order in the source amplitude.
This solution is dual to a remarkably rapid and intriguingly scale dependent
thermalization process in the field theory. When the field theory lives on a
sphere the resultant wave either slowly scatters into a thermal gas (dual to a
glueball type phase in the boundary theory) or rapidly collapses into a black
hole (dual to a plasma type phase in the field theory) depending on the time
scale and amplitude of the source function. The transition between these two
behaviors is sharp and can be tuned to the Choptuik scaling solution in
.Comment: 50 pages + appendices, 6 figures, v2: Minor revisions, references
adde
Emergence of Anti-Cancer Drug Resistance: Exploring the Importance of the Microenvironmental Niche via a Spatial Model
Practically, all chemotherapeutic agents lead to drug resistance. Clinically,
it is a challenge to determine whether resistance arises prior to, or as a
result of, cancer therapy. Further, a number of different intracellular and
microenvironmental factors have been correlated with the emergence of drug
resistance. With the goal of better understanding drug resistance and its
connection with the tumor microenvironment, we have developed a hybrid
discrete-continuous mathematical model. In this model, cancer cells described
through a particle-spring approach respond to dynamically changing oxygen and
DNA damaging drug concentrations described through partial differential
equations. We thoroughly explored the behavior of our self-calibrated model
under the following common conditions: a fixed layout of the vasculature, an
identical initial configuration of cancer cells, the same mechanism of drug
action, and one mechanism of cellular response to the drug. We considered one
set of simulations in which drug resistance existed prior to the start of
treatment, and another set in which drug resistance is acquired in response to
treatment. This allows us to compare how both kinds of resistance influence the
spatial and temporal dynamics of the developing tumor, and its clonal
diversity. We show that both pre-existing and acquired resistance can give rise
to three biologically distinct parameter regimes: successful tumor eradication,
reduced effectiveness of drug during the course of treatment (resistance), and
complete treatment failure
Plasma matrix metalloproteinases in neonates having surgery for congenital heart disease
During cardiopulmonary-bypass matrix-metalloproteinases released may contribute to ventricular dysfunction. This study was to determine plasma matrix-metalloproteinases in neonates after cardiopulmonary-bypass and their relation to post-operative course. A prospective observational study included 18 neonates having cardiac surgery. Plasma matrix-metalloproteinases-2 and 9 activities were measured by gelatin-zymography pre-operatively, on starting cardiopulmonarybypass, 7–8 min after aortic cross-clamp release, and 1h, 4h, 24h, and 3d after cardiopulmonary-bypass. Plasma concentrations of their tissue inhibitors 1 and 2 were determined by enzyme-linked immunosorbent assay. Cardiac function was assessed by serial echocardiography. Paired t-tests and Wilcoxon tests were used to assess temporal changes, and linear correlation with simultaneous clinical and cardiac function parameters were assessed using Pearson's product-moment correlation coefficient. Plasma matrix-metalloproteinases activities and their tissue inhibitor concentrations decreased during cardiopulmonary-bypass. Matrix-metalloproteinase-2 plasma activity increased progressively starting 1h after cardiopulmonarybypass and returned to pre-operative levels at 24h. Matrix-metalloproteinase-9 plasma activity increased significantly after release of aortic cross-clamp, peaked 7–8min later, and returned to baseline at 24h. Plasma tissueinhibitor 1 and 2 concentrations increased 1h after cardiopulmonary-bypass. Cardiac function improved from 4h to 3d after surgery (p<0.05). There was no evidence of significant correlations between matrix-metalloproteinases or their inhibitors and cardiac function, inotrope scores, organ dysfunction scores, ventilation days, or hospital days. The temporal profile of plasma matrix-metalloproteinases and their inhibitors after cardiopulmonary-bypass in neonates are similar to adults. In neonates, further study should determine whether circulating matrix-metalloproteinases are useful biomarkers of disease activity locally within the myocardium, and hence of clinical outcomes
Teleparallel Gravity and Dimensional Reductions of Noncommutative Gauge Theory
We study dimensional reductions of noncommutative electrodynamics on flat
space which lead to gauge theories of gravitation. For a general class of such
reductions, we show that the noncommutative gauge fields naturally yield a
Weitzenbock geometry on spacetime and that the induced diffeomorphism invariant
field theory can be made equivalent to a teleparallel formulation of gravity
which macroscopically describes general relativity. The Planck length is
determined in this setting by the Yang-Mills coupling constant and the
noncommutativity scale. The effective field theory can also contain
higher-curvature and non-local terms which are characteristic of string theory.
Some applications to D-brane dynamics and generalizations to include the
coupling of ordinary Yang-Mills theory to gravity are also described.Comment: 31 pages LaTeX; References adde
Search for a strongly decaying neutral charmed pentaquark
We present a search for a charmed pentaquark decaying strongly to
. Finding no evidence for such a state, we set limits on the cross
section times branching ratio relative to and under particular
assumptions about the production mechanism.Comment: To be published in Physics Letters
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