14469784
Effective field theory approach to N=4 supersymmetric Yang-Mills at finite temperature
We study the perturbation expansion of the free energy of N = 4 supersymmetric SU(N) Yang-Mills at finite temperature in powers of ’t Hooft’s coupling g2N in the large N limit. Infrared divergences are controlled by constructing a hierarchy of two 3 dimensional effective field theories. This procedure is applied to the calculation of the free energy to order (g2N)3/2, but it can be extended to higher order corrections. Agustin.Nieto@cern.ch mtytgat@ulb.ac.be In recent years some light has been shed on understanding the relation between string theory and gauge theories [1]. A particularly interesting system is N coincident, parallel D3-branes. This system realizes N = 4 supersymmetric U(N) Yang-Mills in its world volume (4 dimensions). In the large N limit, the 3-brane system becomes a black brane whose Bekenstein-Hawking entropy can be obtained by considering Ramond-Ramond charged 3brane classical solutions [2]. It is therefore interesting to compare the 3-brane thermodynamics with that of N = 4 supersymmetric U(N) Yang-Mills. The free energy density of N = 4 supersymmetric U(N) Yang-Mills in the ideal gas approximation is Fideal = −π2N2T /6. On the other hand, the free energy of a black 3-brane was found to be [2] FBH = (3/4) ×Fideal. Maldacena’s conjecture [3] helps to understand the relative factor 3/4 between Fideal and FBH. The conjecture relates type IIB superstrings on AdS5 × S to N = 4 supersymmetric SU(N) Yang-Mills in 4 dimensions and allows to compute the next-to-leading order correction to FBH in the strong coupling limit [4], FBH Fideal = 3 4 + 45ζ(3)
1471430
Neutrinos from Inert Doublet dark matter
We investigate the signatures of neutrinos produced in the annihilation of WIMP dark matter in the Earth, the Sun and at the Galactic centre within the framework of the Inert Doublet Model and extensions. We consider a dark matter candidate, that we take to be one of the neutral components of an extra Higgs doublet, in three distinct mass ranges, which have all been shown previously to be consistent with both WMAP abundance and direct detection experiments exclusion limits. Specifically, we consider a light WIMP with mass between 4 and 8 GeV (low), a WIMP with mass around 60-70 GeV (middle) and a heavy WIMP with mass above 500 GeV (high). In the first case, we show that capture in the Sun may be constrained using Super-Kamiokande data. In the last two cases, we argue that indirect detection through neutrinos is challenging but not altogether excluded. For middle masses, we try to make the most benefit of the proximity of the so-called 'iron resonance' that might enhance the capture of the dark matter candidate by the Earth. The signal from the Earth is further enhanced if light right-handed Majorana neutrinos are introduced, in which case the scalar dark matter candidate may annihilate into pairs of mono-energetic neutrinos. In the case of high masses, detection of neutrinos from the Galactic centre might be possible, provided the dark matter abundance is substantially boosted.
119253725
Is the Lorentz limiting speed equal to the speed of light? Photons vs neutrino tests
We discuss the possibility that the “limiting speed” climit (cl) appearing in Lorentz equations might be different (i.e. slightly larger) than the observed speed of light cn. We show that such a possibility can be tested by state-of-the-art Michelson–Morley experiments, but also by careful measurement of neutrino speeds. It would indeed suffice to show that cn<cν≤cl. Quite interestingly, current limits from both approaches are competitive, in some circumstances. We also comment on competing tests using gamma-ray burst, assuming a dispersive character for the propagation of light.
119212974
The inert doublet model: a new archetype of WIMP dark matter?
The Inert Doublet Model (IDM) is a two doublet extension of the Higgs-Brout-Englert sector of the Standard Model with a Z2 symmetry in order to prevent FCNC. If the Z2 symmetry is not spontaneously broken, the lightest neutral extra scalar is a dark matter candidate. We briefly review the phenomenology of the model, emphasizing its relevance for the issue of Electroweak Symmetry Breaking (EWSB) and the prospects for detection of dark matter.
119148641
Electroweak symmetry breaking induced by dark matter
Abstract The mechanism behind electroweak symmetry breaking (EWSB) and the nature of dark matter (DM) are currently among the most important issues in high energy physics. Since a natural dark matter candidate is a weakly interacting massive particle or WIMP, with mass around the electroweak scale, it is clearly of interest to investigate the possibility that DM and EWSB are closely related. In the context of a very simple extension of the Standard Model, the inert doublet model, we show that dark matter could play a crucial role in the breaking of the electroweak symmetry. In this model, dark matter is the lightest component of an inert scalar doublet. The coupling of the latter with the Standard Model Higgs doublet breaks the electroweak symmetry at one-loop, a la Coleman–Weinberg . The abundance of dark matter, the breaking of the electroweak symmetry and the constraints from electroweak precision measurements can all be accommodated by imposing (an exact or approximate) custodial symmetry.
119198386
Scalar dark matter models with significant internal bremsstrahlung
There has been interest recently on particle physics models that may give rise to sharp gamma ray spectral features from dark matter annihilation. Because dark matter is supposed to be electrically neutral, it is challenging to build weakly interacting massive particle models that may accommodate both a large cross section into gamma rays at, say, the Galactic center, and the right dark matter abundance. In this work, we consider the gamma ray signatures of a class of scalar dark matter models that interact with Standard Model dominantly through heavy vector-like fermions (the vector-like portal). We focus on a real scalar singlet S annihilating into lepton-antilepton pairs. Because this two-body final-state annihilation channel is d-wave suppressed in the chiral limit, σfv∝v4, we show that virtual internal bremsstrahlung emission of a gamma ray gives a large correction, both today and at the time of freeze-out. For the sake of comparison, we confront this scenario to the familiar case of a Majorana singlet annihilating into light lepton-antilepton pairs, and show that the virtual internal bremsstrahlung signal may be enhanced by a factor of (up to) two orders of magnitude. We discuss the scope and possible generalizations of the model.
15360804
SUSY Searches in All-Hadronic States with Large MET at the LHC
The CMS and ATLAS search strategy for SUSY in inclusive multijet plus high missing transverse energy final states is reviewed. This canonical SUSY signature may be a viable discovery channel for low mass SUSY in the early phase of the LHC. Methods for Standard Model background estimates, MET studies and filters for instrumental background are presented.
122512363
Exclusive meson production at HERMES
Abstract.Hard exclusive production of mesons in deep-inelastic scattering allows one to probe the so-far unknown Generalized Parton Distributions (GPDs) of the nucleon. The HERMES experiment has measured several different observables in exclusive meson production by scattering the 27.6GeV HERA lepton beam off an internal fixed gaseous target. Recent results on exclusive π+, ρ0 and pion pair production will be presented.
55047377
Optical characterization of n = 1.03 silica aerogel used as radiator in the RICH of HERMES
The optical properties of silica aerogel tiles with a refractive index of 1.03 and dimensions 11]11] 1c m 3, produced by the Matsushita Electric Works (Japan), have been measured in the wavelength range from 200 to 900 nm. The tiles are used as one of the two radiators of the ring imaging Cherenkov counter of the HERMES experiment at DESY-HERA. The transmittance of light has been measured on 200 tiles by means of a double beam spectrophotometer. The light trans#ectance and re#ectance have been measured on one tile by means of a single-beam spectrophotometer and an integrating re#ecting sphere. Typical values of the measured transmittances at a wavelength j"400 nm are around 0.67. The measured trans#ectance increases almost linearly from 0.4 to 0.96 in the interval 200}300 nm, and remains nearly constant at the value 0.95 in the complementary j-range. The measured re#ectance, mostly con"ned below 400 nm, is completely interpretable as backscattering from inside the aerogel, revealing an absence of light re#ection at the aerogel surfaces. The transmittance data have been "tted with the Hunt formula, whose parameters have been used to evaluate the number of unscattered and scattered Cherenkov photons produced by aerogel. For stacks of 5 tiles and quantum
202096488
Particle identification with the HERMES RICH
Abstract In early 1998 a dual-radiator RICH detector was installed into the HERMES spectrometer. It is designed to allow hadron identification over the HERMES kinematic range (2–20 GeV) using both an aerogel and C 4 F 10 gas radiator. Three different approaches that are currently pursued for particle identification are presented.
119748220
New results from hermes