13,836 research outputs found
Further search for a neutral boson with a mass around 9 MeV/c2
Two dedicated experiments on internal pair conversion (IPC) of isoscalar M1
transitions were carried out in order to test a 9 MeV/c2 X-boson scenario. In
the 7Li(p,e+e-)8Be reaction at 1.1 MeV proton energy to the predominantly T=0
level at 18.15 MeV, a significant deviation from IPC was observed at large pair
correlation angles. In the 11B(d,n e+e-)12C reaction at 1.6 MeV, leading to the
12.71 MeV 1+ level with pure T=0 character, an anomaly was observed at 9
MeV/c2. The compatibility of the results with the scenario is discussed.Comment: 12 pages, 5 figures, 2 table
Comment on "1/f noise in the Bak-Sneppen model"
Contrary to the recently published results by Daerden and Vanderzande [Phys.
Rev. E 53, 4723 (1996)], we show that the time correlation function in the
random-neighbor version of the Bak-Sneppen model can be well approximated by an
exponential giving rise to a 1/f2 power spectrum.Comment: 2 pages, 2 figure
An algorithm for calculating the Lorentz angle in silicon detectors
Future experiments will use silicon sensors in the harsh radiation
environment of the LHC (Large Hadron Collider) and high magnetic fields. The
drift direction of the charge carriers is affected by the Lorentz force due to
the high magnetic field. Also the resulting radiation damage changes the
properties of the drift.
In this paper measurements of the Lorentz angle of electrons and holes before
and after irradiation are reviewed and compared with a simple algorithm to
compute the Lorentz angle.Comment: 13 pages, 7 figures, final version accepted by NIMA. Mainly
clarifications included and slightly shortene
Where is SUSY?
The direct searches for Superymmetry at colliders can be complemented by
direct searches for dark matter (DM) in underground experiments, if one assumes
the Lightest Supersymmetric Particle (LSP) provides the dark matter of the
universe. It will be shown that within the Constrained minimal Supersymmetric
Model (CMSSM) the direct searches for DM are complementary to direct LHC
searches for SUSY and Higgs particles using analytical formulae. A combined
excluded region from LHC, WMAP and XENON100 will be provided, showing that
within the CMSSM gluinos below 1 TeV and LSP masses below 160 GeV are excluded
(m_{1/2} > 400 GeV) independent of the squark masses.Comment: 16 pages, 10 figure
Low Mass Dark Matter and Invisible Higgs Width In Darkon Models
The Standard Model (SM) plus a real gauge-singlet scalar field dubbed darkon
(SM+D) is the simplest model possessing a weakly interacting massive particle
(WIMP) dark-matter candidate. In this model, the parameters are constrained
from dark matter relic density and direct searches. The fact that interaction
between darkon and SM particles is only mediated by Higgs boson exchange may
lead to significant modifications to the Higgs boson properties. If the dark
matter mass is smaller than a half of the Higgs boson mass, the Higgs boson can
decay into a pair of darkons resulting in a large invisible branching ratio.
The Higgs boson will be searched for at the LHC and may well be discovered in
the near future. If a Higgs boson with a small invisible decay width will be
found, the SM+D model with small dark matter mass will be in trouble. We find
that by extending the SM+D to a two-Higgs-doublet model plus a darkon (THDM+D)
it is possible to have a Higgs boson with a small invisible branching ratio and
at the same time the dark matter can have a low mass. We also comment on other
implications of this model.Comment: RevTeX, 15 pages, 11 figures. A few typos corrected and some
references adde
Search for SUSY in (Leptons +) Jets + E_T^miss final states
We study the observability of the squarks and gluinos in CMS at LHC.
Classical E_T^miss + jets final state as well as a number of additional
multilepton signatures (0 leptons, 1 lepton, 2 leptons of the same sign, 2
leptons of the opposite sign and 3 leptons) are investigated . The detection of
these sparticles relies on the observation of an excess of events over Standard
Model background expectations. The study is made in the framework of a minimal
SU(5) mSUGRA model as a function of m_0, m_1/2 for 4 sets of model parameters :
tan(beta) = 2 or 35 and sign(mu) = +/- 1 and for fixed value of A_0 = 0. The
CMS detector response is modelled using CMSJET 4.51 fast MC code (non-GEANT).
The results obtained are presented as 5 sigma detection contours in the m_0,
m_1/2 planes and with optimized selection cuts in various regions of the
parameter space. The result of these investigations is that with integrated
luminosity L=10^5 pb^-1 the squark and gluino mass reach is about 2.5 TeV and
covers most of the interesting parts of parameter space according to neutralino
relic density expectations. The influence of signal and background
cross-section uncertainties on the reach contours is estimated. The effect of
pile-up on signal and background is also discussed. This effect is found to be
insignificant for E_T^miss and single lepton signatures, whilst only a minor
deterioration is seen for multilepton final states.Comment: 28 pages, 28 figure
U(N|M) quantum mechanics on Kaehler manifolds
We study the extended supersymmetric quantum mechanics, with supercharges
transforming in the fundamental representation of U(N|M), as realized in
certain one-dimensional nonlinear sigma models with Kaehler manifolds as target
space. We discuss the symmetry algebra characterizing these models and, using
operatorial methods, compute the heat kernel in the limit of short propagation
time. These models are relevant for studying the quantum properties of a
certain class of higher spin field equations in first quantization.Comment: 21 pages, a reference adde
A fixed point formula for the index of multi-centered N=2 black holes
We propose a formula for computing the (moduli-dependent) contribution of
multi-centered solutions to the total BPS index in terms of the
(moduli-independent) indices associated to single-centered solutions. The main
tool in our analysis is the computation of the refined index Tr(-y)^{2J_3} of
configurational degrees of freedom of multi-centered BPS black hole solutions
in N=2 supergravity by localization methods. When the charges carried by the
centers do not allow for scaling solutions (i.e. solutions where a subset of
the centers can come arbitrarily close to each other), the phase space of
classical BPS solutions is compact and the refined index localizes to a finite
set of isolated fixed points under rotations, corresponding to collinear
solutions. When the charges allow for scaling solutions, the phase space is
non-compact but appears to admit a compactification with finite volume and
additional non-isolated fixed points. We give a prescription for determining
the contributions of these fixed submanifolds by means of a `minimal
modification hypothesis', which we prove in the special case of dipole halo
configurations.Comment: 61 pages, 3 figure
The inner environment of Z~CMa: High-Contrast Imaging Polarimetry with NaCo
Context. Z\,CMa is a binary composed of an embedded Herbig Be and an FU Ori
class star separated by au. Observational evidence indicate a complex
environment in which each star has a circumstellar disk and drives a jet, and
the whole system is embedded in a large dusty envelope.
Aims. We aim to probe the circumbinary environment of Z\,CMa in the inner 400
au in scattered light.
Methods. We use high contrast imaging polarimetry with VLT/NaCo at and
bands.
Results. The central binary is resolved in both bands. The polarized images
show three bright and complex structures: a common dust envelope, a sharp
extended feature previously reported in direct light, and an intriguing bright
clump located 0\farcs3 south of the binary, which appears spatially connected
to the sharp extended feature.
Conclusions.We detect orbital motion when compared to previous observations,
and report a new outburst driven by the Herbig star. Our observations reveal
the complex inner environment of Z\,CMa with unprecedented detail and contrast.Comment: Accepted for publication in A&A Letter
The Rapidly Rotating, Hydrogen Deficient, Hot Post-Asymptotic Giant Branch Star ZNG 1 in the Globular Cluster M5
We report observations of the hot post-asymptotic giant branch star ZNG 1 in
the globular cluster M5 (NGC 5904) with the Far Ultraviolet Spectroscopic
Explorer (FUSE). From the resulting spectrum, we derive an effective
temperature T_eff = 44300 +/- 300 K, a surface gravity log g = 4.3 +/- 0.1, a
rotational velocity v sin i = 170 +/- 20 km/s, and a luminosity log (L/L_sun) =
3.52 +/- 0.04. The atmosphere is helium-rich (Y = 0.93), with enhanced carbon
(2.6% by mass), nitrogen (0.51%) and oxygen (0.37%) abundances. The spectrum
shows evidence for a wind with terminal velocity near 1000 km/s and an
expanding shell of carbon- and nitrogen-rich material around the star. The
abundance pattern of ZNG 1 is suggestive of the ``born-again'' scenario,
whereby a star on the white-dwarf cooling curve undergoes a very late shell
flash and returns to the AGB, but the star's rapid rotation is more easily
explained by a previous interaction with a binary companion.Comment: 8 pages, 2 PostScript figures, Latex with emulateapj5. Accepted for
publication in ApJ Letter
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