7,506 research outputs found
A new limit on the Ultra-High-Energy Cosmic-Ray flux with the Westerbork Synthesis Radio Telescope
A particle cascade (shower) in a dielectric, for example as initiated by an
ultra-high energy cosmic ray, will have an excess of electrons which will emit
coherent \v{C}erenkov radiation, known as the Askaryan effect. In this work we
study the case in which such a particle shower occurs in a medium just below
its surface. We show, for the first time, that the radiation transmitted
through the surface is independent of the depth of the shower below the surface
when observed from far away, apart from trivial absorption effects. As a direct
application we use the recent results of the NuMoon project, where a limit on
the neutrino flux for energies above \,eV was set using the Westerbork
Synthesis Radio Telescope by measuring pulsed radio emission from the Moon, to
set a limit on the flux of ultra-high-energy cosmic rays.Comment: Accepted for publication in Phys. Rev.
Implications of Improved Higgs Mass Calculations for Supersymmetric Models
We discuss the allowed parameter spaces of supersymmetric scenarios in light
of improved Higgs mass predictions provided by FeynHiggs 2.10.0. The Higgs mass
predictions combine Feynman-diagrammatic results with a resummation of leading
and subleading logarithmic corrections from the stop/top sector, which yield a
significant improvement in the region of large stop masses. Scans in the pMSSM
parameter space show that, for given values of the soft supersymmetry-breaking
parameters, the new logarithmic contributions beyond the two-loop order
implemented in FeynHiggs tend to give larger values of the light CP-even Higgs
mass, M_h, in the region of large stop masses than previous predictions that
were based on a fixed-order Feynman-diagrammatic result, though the differences
are generally consistent with the previous estimates of theoretical
uncertainties. We re-analyze the parameter spaces of the CMSSM, NUHM1 and
NUHM2, taking into account also the constraints from CMS and LHCb measurements
of B_s to \mu+\mu- and ATLAS searches for MET events using 20/fb of LHC data at
8 TeV. Within the CMSSM, the Higgs mass constraint disfavours tan beta lesssim
10, though not in the NUHM1 or NUHM2.Comment: 22 pages, 17 figure
The NUHM2 after LHC Run 1
We make a frequentist analysis of the parameter space of the NUHM2, in which
the soft supersymmetry (SUSY)-breaking contributions to the masses of the two
Higgs multiplets, , vary independently from the universal soft
SUSY-breaking contributions to the masses of squarks and sleptons. Our
analysis uses the MultiNest sampling algorithm with over points
to sample the NUHM2 parameter space. It includes the ATLAS and CMS Higgs mass
measurements as well as their searches for supersymmetric jets + MET signals
using the full LHC Run~1 data, the measurements of by
LHCb and CMS together with other B-physics observables, electroweak precision
observables and the XENON100 and LUX searches for spin-independent dark matter
scattering. We find that the preferred regions of the NUHM2 parameter space
have negative SUSY-breaking scalar masses squared for squarks and sleptons,
, as well as . The tension present in the
CMSSM and NUHM1 between the supersymmetric interpretation of and
the absence to date of SUSY at the LHC is not significantly alleviated in the
NUHM2. We find that the minimum with 21 degrees of freedom
(dof) in the NUHM2, to be compared with in the
CMSSM, and in the NUHM1. We find that the
one-dimensional likelihood functions for sparticle masses and other observables
are similar to those found previously in the CMSSM and NUHM1.Comment: 20 pages latex, 13 figure
Photonic band structure of highly deformable, self-assembling systems
We calculate the photonic band structure at normal incidence of highly
deformable, self-assembling systems - cholesteric elastomers subjected to
external stress. Cholesterics display brilliant reflection and lasing owing to
gaps in their photonic band structure. The band structure of cholesteric
elastomers varies sensitively with strain, showing new gaps opening up and
shifting in frequency. A novel prediction of a total band gap is made, and is
expected to occur in the vicinity of the previously observed de Vries bandgap,
which is only for one polarisation
Supersymmetric Dark Matter after LHC Run 1
Different mechanisms operate in various regions of the MSSM parameter space
to bring the relic density of the lightest neutralino, neutralino_1, assumed
here to be the LSP and thus the Dark Matter (DM) particle, into the range
allowed by astrophysics and cosmology. These mechanisms include coannihilation
with some nearly-degenerate next-to-lightest supersymmetric particle (NLSP)
such as the lighter stau (stau_1), stop (stop_1) or chargino (chargino_1),
resonant annihilation via direct-channel heavy Higgs bosons H/A, the light
Higgs boson h or the Z boson, and enhanced annihilation via a larger Higgsino
component of the LSP in the focus-point region. These mechanisms typically
select lower-dimensional subspaces in MSSM scenarios such as the CMSSM, NUHM1,
NUHM2 and pMSSM10. We analyze how future LHC and direct DM searches can
complement each other in the exploration of the different DM mechanisms within
these scenarios. We find that the stau_1 coannihilation regions of the CMSSM,
NUHM1, NUHM2 can largely be explored at the LHC via searches for missing E_T
events and long-lived charged particles, whereas their H/A funnel, focus-point
and chargino_1 coannihilation regions can largely be explored by the LZ and
Darwin DM direct detection experiments. We find that the dominant DM mechanism
in our pMSSM10 analysis is chargino_1 coannihilation: {parts of its parameter
space can be explored by the LHC, and a larger portion by future direct DM
searches.Comment: 21 pages, 8 figure
Light scattering from three-level systems: The T-matrix of a point-dipole with gain
We present an extension of the T-matrix approach to scattering of light by a
three-level system, using a description based on a Master equation. More
particularly, we apply our formalism to calculate the T-matrix of a pumped
three-level atom, providing an exact and analytical expression describing the
influence of a pump on the light scattering properties of an atomic three-level
system
Gammaâray burst studies by COMPTEL during its first year of operation
During the first year of Compton GRO operations, more than 20 cosmic gammaâray burstâdetected by the BATSE instrument â occurred inside the 1 sr field of view of the imaging gammaâray telescope COMPTEL. Using COMPTELâs primary mode of operation (the telescope mode) direct images (with âŒ1° GRB location accuracy) and event spectra (0.7 MeV â 30 MeV) with spectral resolution better than 10% FWHM have been obtained. In its secondary mode of burst operations, COMPTEL has recorded time resolved spectra (0.1 MeV â 10 MeV) from its large NaI detectors. This paper summarises the results on cosmic GRB sources obtained by COMPTEL during its first year of operation
The pMSSM10 after LHC Run 1
We present a frequentist analysis of the parameter space of the pMSSM10, in
which the following 10 soft SUSY-breaking parameters are specified
independently at the mean scalar top mass scale Msusy = Sqrt[M_stop1 M_stop2]:
the gaugino masses M_{1,2,3}, the 1st-and 2nd-generation squark masses M_squ1 =
M_squ2, the third-generation squark mass M_squ3, a common slepton mass M_slep
and a common trilinear mixing parameter A, the Higgs mixing parameter mu, the
pseudoscalar Higgs mass M_A and tan beta. We use the MultiNest sampling
algorithm with 1.2 x 10^9 points to sample the pMSSM10 parameter space. A
dedicated study shows that the sensitivities to strongly-interacting SUSY
masses of ATLAS and CMS searches for jets, leptons + MET signals depend only
weakly on many of the other pMSSM10 parameters. With the aid of the Atom and
Scorpion codes, we also implement the LHC searches for EW-interacting
sparticles and light stops, so as to confront the pMSSM10 parameter space with
all relevant SUSY searches. In addition, our analysis includes Higgs mass and
rate measurements using the HiggsSignals code, SUSY Higgs exclusion bounds, the
measurements B-physics observables, EW precision observables, the CDM density
and searches for spin-independent DM scattering. We show that the pMSSM10 is
able to provide a SUSY interpretation of (g-2)_mu, unlike the CMSSM, NUHM1 and
NUHM2. As a result, we find (omitting Higgs rates) that the minimum chi^2/dof =
20.5/18 in the pMSSM10, corresponding to a chi^2 probability of 30.8 %, to be
compared with chi^2/dof = 32.8/24 (31.1/23) (30.3/22) in the CMSSM (NUHM1)
(NUHM2). We display 1-dimensional likelihood functions for SUSY masses, and
show that they may be significantly lighter in the pMSSM10 than in the CMSSM,
NUHM1 and NUHM2. We discuss the discovery potential of future LHC runs, e+e-
colliders and direct detection experiments.Comment: 47 pages, 29 figure
COMPTEL observations of cosmic gammaâray bursts
The imaging Îłâray telescope COMPTEL on board NASAâs Compton GammaâRay Observatory (GRO) has observed many cosmic gammaâray bursts during the early mission phase of GRO. COMPTEL records timeâresolved burst spectra over 0.1 MeV to 10 MeV energies, and, for the first time, produces direct singleâtelescope gammaâray images (0.8â30 MeV) of cosmic gammaâray bursts occurring in its 1 sr field of field
Radio Sources in Galaxy Clusters at 28.5 GHz
We present serendipitous detections of radio sources at 28.5 GHz (1 cm),
which resulted from our program to image thermal Sunyaev-Zeldovich (SZ) effect
in 56 galaxy clusters. We find 64 radio sources with fluxes down to 0.4 mJy,
and within 250 arcseconds from the pointing centers. The spectral indices (S ~
\nu^-\alpha) of 54 sources with published low frequency flux densities range
from -0.6 to 2 with a mean of 0.77, and a median of 0.84. Extending low
frequency surveys of radio sources towards galaxy clusters CL 0016+16, Abell
665, and Abell 2218 to 28.5 GHz, and selecting sources with 1.4 GHz flux
density greater than 7 mJy to form an unbiased sample, we find a mean spectral
index of 0.71 and a median of 0.71. We find 4 to 7 times more sources predicted
from a low frequency survey in areas without galaxy clusters. This excess
cannot be accounted for by gravitational lensing of a background radio
population by cluster potentials, indicating most of the detected sources are
associated with galaxy clusters. For the cluster Abell 2218, the presence of
unsubtracted radio sources with 28.5 GHz flux densities less than 0.5 mJy, can
only contribute to temperature fluctuations at a level of 10 to 25 \muK. The
corresponding error due to radio point source contamination in the Hubble
constant derived through a combined analysis of 28.5 GHz SZ images and X-ray
emission observations ranges from 1% to 6%.Comment: 18 pages, 8 figures, to appear in April 1998 issue of A
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