2,227 research outputs found
Massive amplitudes on the Coulomb branch of N=4 SYM
We initiate a systematic study of amplitudes with massive external particles
on the Coulomb-branch of N=4 super Yang Mills theory: 1) We propose that
(multi-)soft-scalar limits of massless amplitudes at the origin of moduli space
can be used to determine Coulomb-branch amplitudes to leading order in the
mass. This is demonstrated in numerous examples. 2) We find compact explicit
expressions for several towers of tree-level amplitudes, including scattering
of two massive W-bosons with any number of positive helicity gluons, valid for
all values of the mass. 3) We present the general structure of superamplitudes
on the Coulomb branch. For example, the n-point "MHV-band" superamplitude is
proportional to a Grassmann polynomial of mixed degree 4 to 12, which is
uniquely determined by supersymmetry. We find explicit tree-level
superamplitudes for this MHV band and for other simple sectors of the theory.
4) Dual conformal generators are constructed, and we explore the dual conformal
properties of the simplest massive amplitudes. Our compact expressions for
amplitudes and superamplitudes should be of both theoretical and
phenomenological interest; in particular the tree-level results carry over to
truncations of the theory with less supersymmetry.Comment: 29 pages, 1 figur
Thermodynamics and Instabilities of a Strongly Coupled Anisotropic Plasma
We extend our analysis of a IIB supergravity solution dual to a spatially
anisotropic finite-temperature N=4 super Yang-Mills plasma. The solution is
static, possesses an anisotropic horizon, and is completely regular. The full
geometry can be viewed as a renormalization group flow from an AdS geometry in
the ultraviolet to a Lifshitz-like geometry in the infrared. The anisotropy can
be equivalently understood as resulting from a position-dependent theta-term or
from a non-zero number density of dissolved D7-branes. The holographic stress
tensor is conserved and anisotropic. The presence of a conformal anomaly plays
an important role in the thermodynamics. The phase diagram exhibits homogeneous
and inhomogeneous (i.e. mixed) phases. In some regions the homogeneous phase
displays instabilities reminiscent of those of weakly coupled plasmas. We
comment on similarities with QCD at finite baryon density and with the
phenomenon of cavitation.Comment: 62 pages, 13 figures; v2: typos fixed, added reference
Holographic entanglement entropy in AdS4/BCFT3 and the Willmore functional
We study the holographic entanglement entropy of spatial regions having arbitrary shapes in the AdS4/BCFT3 correspondence with static gravitational backgrounds, focusing on the subleading term with respect to the area law term in its expansion as the UV cutoff vanishes. An analytic expression depending on the unit vector normal to the minimal area surface anchored to the entangling curve is obtained. When the bulk spacetime is a part of AdS4, this formula becomes the Willmore functional with a proper boundary term evaluated on the minimal surface viewed as a submanifold of a three dimensional flat Euclidean space with boundary. For some smooth domains, the analytic expressions of the finite term are reproduced, including the case of a disk disjoint from a boundary which is either flat or circular. When the spatial region contains corners adjacent to the boundary, the subleading term is a logarithmic divergence whose coefficient is determined by a corner function that is known analytically, and this result is also recovered. A numerical approach is employed to construct extremal surfaces anchored to entangling curves with arbitrary shapes. This analysis is used both to check some analytic results and to find numerically the finite term of the holographic entanglement entropy for some ellipses at finite distance from a flat boundary
S100B as a potential biomarker and therapeutic target in multiple sclerosis
Multiple sclerosis (MS) pathology is characterized by neuroinflammation and demyelination. Recently, the inflammatory molecule S100B was identified in cerebrospinal fluid (CSF) and serum of MS patients. Although seen as an astrogliosis marker, lower/physiological levels of S100B are involved in oligodendrocyte differentiation/maturation. Nevertheless, increased S100B levels released upon injury may induce glial reactivity and oligodendrocyte demise, exacerbating tissue damage during an MS episode or delaying the following remyelination. Here, we aimed to unravel the functional role of S100B in the pathogenesis of MS. Elevated S100B levels were detected in the CSF of relapsing-remitting MS patients at diagnosis. Active demyelinating MS lesions showed increased expression of S100B and its receptor, the receptor for advanced glycation end products (RAGE), in the lesion area, while chronic active lesions displayed increased S100B in demyelinated areas with lower expression of RAGE in the rim. Interestingly, reactive astrocytes were identified as the predominant cellular source of S100B, whereas RAGE was expressed by activated microglia/macrophages. Using an ex vivo demyelinating model, cerebral organotypic slice cultures treated with lysophosphatidylcholine (LPC), we observed a marked elevation of S100B upon demyelination, which co-localized mostly with astrocytes. Inhibition of S100B action using a directed antibody reduced LPC-induced demyelination, prevented astrocyte reactivity and abrogated the expression of inflammatory and inflammasome-related molecules. Overall, high S100B expression in MS patient samples suggests its usefulness as a diagnostic biomarker for MS, while the beneficial outcome of its inhibition in our demyelinating model indicates S100B as an emerging therapeutic target in MS.This work was supported by Medal of Honor L’Oréal
for Women in Science (FCT, UNESCO, L’Óreal) and innovation
grant (Ordem dos Farmacêuticos) to AF, a post-doctoral grant from
Fundação para a Ciência e Tecnologia (FCT-SFRH/BPD/96794/2013)
and a DuPré Grant from the European Committee for Treatment and
Research in Multiple Sclerosis (ECTRIMS) to AB, and by FCT-Pest-
OE/SAU/UI4013 to iMed.ULisboa.info:eu-repo/semantics/publishedVersio
Measurement of the branching fraction and CP content for the decay B(0) -> D(*+)D(*-)
This is the pre-print version of the Article. The official published version can be accessed from the links below. Copyright @ 2002 APS.We report a measurement of the branching fraction of the decay B0→D*+D*- and of the CP-odd component of its final state using the BABAR detector. With data corresponding to an integrated luminosity of 20.4 fb-1 collected at the Υ(4S) resonance during 1999–2000, we have reconstructed 38 candidate signal events in the mode B0→D*+D*- with an estimated background of 6.2±0.5 events. From these events, we determine the branching fraction to be B(B0→D*+D*-)=[8.3±1.6(stat)±1.2(syst)]×10-4. The measured CP-odd fraction of the final state is 0.22±0.18(stat)±0.03(syst).This work is supported by DOE and NSF (USA), NSERC (Canada), IHEP (China), CEA and CNRS-IN2P3 (France), BMBF (Germany), INFN (Italy), NFR (Norway), MIST (Russia), and PPARC (United Kingdom). Individuals have received support from the A.P. Sloan Foundation, Research Corporation, and Alexander von Humboldt Foundation
A search for the decay modes B+/- to h+/- tau l
We present a search for the lepton flavor violating decay modes B+/- to h+/-
tau l (h= K,pi; l= e,mu) using the BaBar data sample, which corresponds to 472
million BBbar pairs. The search uses events where one B meson is fully
reconstructed in one of several hadronic final states. Using the momenta of the
reconstructed B, h, and l candidates, we are able to fully determine the tau
four-momentum. The resulting tau candidate mass is our main discriminant
against combinatorial background. We see no evidence for B+/- to h+/- tau l
decays and set a 90% confidence level upper limit on each branching fraction at
the level of a few times 10^-5.Comment: 15 pages, 7 figures, submitted to Phys. Rev.
Diffractive Dijet Production at sqrt(s)=630 and 1800 GeV at the Fermilab Tevatron
We report a measurement of the diffractive structure function of
the antiproton obtained from a study of dijet events produced in association
with a leading antiproton in collisions at GeV at the
Fermilab Tevatron. The ratio of at GeV to
obtained from a similar measurement at GeV is compared with
expectations from QCD factorization and with theoretical predictions. We also
report a measurement of the (-Pomeron) and ( of parton in
Pomeron) dependence of at GeV. In the region
, GeV and , is
found to be of the form , which obeys
- factorization.Comment: LaTeX, 9 pages, Submitted to Phys. Rev. Letter
Evidence for an excess of B -> D(*) Tau Nu decays
Based on the full BaBar data sample, we report improved measurements of the
ratios R(D(*)) = B(B -> D(*) Tau Nu)/B(B -> D(*) l Nu), where l is either e or
mu. These ratios are sensitive to new physics contributions in the form of a
charged Higgs boson. We measure R(D) = 0.440 +- 0.058 +- 0.042 and R(D*) =
0.332 +- 0.024 +- 0.018, which exceed the Standard Model expectations by 2.0
sigma and 2.7 sigma, respectively. Taken together, our results disagree with
these expectations at the 3.4 sigma level. This excess cannot be explained by a
charged Higgs boson in the type II two-Higgs-doublet model. We also report the
observation of the decay B -> D Tau Nu, with a significance of 6.8 sigma.Comment: Expanded section on systematics, text corrections, improved the
format of Figure 2 and included the effect of the change of the Tau
polarization due to the charged Higg
Measurement of D-s(+) and D-s(*+) production in B meson decays and from continuum e(+)e(-) annihilation at √s=10.6 GeV
This is the pre-print version of the Article. The official published version can be accessed from the links below. Copyright @ 2002 APSNew measurements of Ds+ and Ds*+ meson production rates from B decays and from qq̅ continuum events near the Υ(4S) resonance are presented. Using 20.8 fb-1 of data on the Υ(4S) resonance and 2.6 fb-1 off-resonance, we find the inclusive branching fractions B(B⃗Ds+X)=(10.93±0.19±0.58±2.73)% and B(B⃗Ds*+X)=(7.9±0.8±0.7±2.0)%, where the first error is statistical, the second is systematic, and the third is due to the Ds+→φπ+ branching fraction uncertainty. The production cross sections σ(e+e-→Ds+X)×B(Ds+→φπ+)=7.55±0.20±0.34pb and σ(e+e-→Ds*±X)×B(Ds+→φπ+)=5.8±0.7±0.5pb are measured at center-of-mass energies about 40 MeV below the Υ(4S) mass. The branching fractions ΣB(B⃗Ds(*)+D(*))=(5.07±0.14±0.30±1.27)% and ΣB(B⃗Ds*+D(*))=(4.1±0.2±0.4±1.0)% are determined from the Ds(*)+ momentum spectra. The mass difference m(Ds+)-m(D+)=98.4±0.1±0.3MeV/c2 is also measured.This work was supported by DOE and NSF (USA), NSERC (Canada), IHEP (China), CEA and CNRS-IN2P3 (France), BMBF (Germany), INFN (Italy), NFR (Norway), MIST (Russia), and PPARC (United Kingdom). Individuals have received support from the Swiss NSF, A. P. Sloan Foundation, Research Corporation, and Alexander von Humboldt Foundation
Search for the decay modes D^0 → e^+e^-, D^0 → μ^+μ^-, and D^0 → e^±μ∓
We present searches for the rare decay modes D^0→e^+e^-, D^0→μ^+μ^-, and D^0→e^±μ^∓ in continuum e^+e^-→cc events recorded by the BABAR detector in a data sample that corresponds to an integrated luminosity of 468 fb^(-1). These decays are highly Glashow–Iliopoulos–Maiani suppressed but may be enhanced in several extensions of the standard model. Our observed event yields are consistent with the expected backgrounds. An excess is seen in the D^0→μ^+μ^- channel, although the observed yield is consistent with an upward background fluctuation at the 5% level. Using the Feldman–Cousins method, we set the following 90% confidence level intervals on the branching fractions: B(D^0→e^+e^-)<1.7×10^(-7), B(D^0→μ^+μ^-) within [0.6,8.1]×10^(-7), and B(D^0→e^±μ^∓)<3.3×10^(-7)
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