472 research outputs found
Dissipative Liouville Cosmology: A Case Study
We consider solutions of the cosmological equations pertaining to a
dissipative, dilaton-driven off-equilibrium Liouville Cosmological model, which
may describe the effective field theoretic limit of a non-critical string model
of the Universe. The non-criticality may be the result of an early-era
catastrophic cosmic event, such as a big-bang, brane-world collision etc. The
evolution of the various cosmological parameters of the model are obtained, and
the effects of the dilaton and off-shell Liouville terms, including briefly
those on relic densities, which distinguish the model from conventional
cosmologies, are emphasised.Comment: 19 pages latex, 11 eps figures incorporate
Estimates of hadron azimuthal anisotropy from multiparton interactions in proton-proton collisions at sqrt(s) = 14 TeV
We estimate the amount of collective "elliptic flow" expected at mid-rapidity
in proton-proton (p-p) collisions at the CERN Large Hadron Collider (LHC),
assuming that any possible azimuthal anisotropy of the produced hadrons with
respect to the plane of the reaction follows the same overlap-eccentricity and
particle-density scalings as found in high-energy heavy ion collisions. Using a
Glauber eikonal model, we compute the p-p eccentricities, transverse areas and
particle-multiplicities for various phenomenological parametrisations of the
proton spatial density. For realistic proton transverse profiles, we find
integrated elliptic flow v2 parameters below 3% in p-p collisions at sqrt(s) =
14 TeV.Comment: 17 pages, 9 figures. Very minor mods. Version to appear in EPJ-
TeV-scale bileptons, see-saw type II and lepton flavor violation in core-collapse supernova
Electrons and electron neutrinos in the inner core of the core-collapse
supernova are highly degenerate and therefore numerous during a few seconds of
explosion. In contrast, leptons of other flavors are non-degenerate and
therefore relatively scarce. This is due to lepton flavor conservation. If this
conservation law is broken by some non-standard interactions, electron
neutrinos are converted to muon and tau-neutrinos, and electrons - to muons.
This affects the supernova dynamics and the supernova neutrino signal. We
consider lepton flavor violating interactions mediated by scalar bileptons,
i.e. heavy scalars with lepton number 2. It is shown that in case of TeV-mass
bileptons the electron fermi gas is equilibrated with non-electron species
inside the inner supernova core at a time-scale of order of (1-100) ms. In
particular, a scalar triplet which generates neutrino masses through the
see-saw type II mechanism is considered. It is found that supernova core is
sensitive to yet unprobed values of masses and couplings of the triplet.Comment: accepted to Eur.Phys.J.
A Phenomenological Analysis of Gluon Mass Effects in Inclusive Radiative Decays of the and $\Upsilon
The shapes of the inclusive photon spectra in the processes \Jp \to \gamma
X and \Up \to \gamma X have been analysed using all available experimental
data.
Relativistic, higher order QCD and gluon mass corrections were taken into
account in the fitted functions. Only on including the gluon mass corrections,
were consistent and acceptable fits obtained. Values of
GeV and GeV were found for the
effective gluon masses (corresponding to Born level diagrams) for the \Jp and
\Up respectively. The width ratios \Gamma(V \to {\rm hadrons})/\Gamma(V \to
\gamma+ {\rm hadrons}) V=\Jp, \Up were used to determine and . Values consistent with the current world
average were obtained only when gluon mass correction factors,
calculated using the fitted values of the effective gluon mass, were applied. A
gluon mass GeV, as suggested with these results, is consistent with
previous analytical theoretical calculations and independent phenomenological
estimates, as well as with a recent, more accurate, lattice calculation of the
gluon propagator in the infra-red region.Comment: 50 pages, 11 figures, 15 table
Growth and mortality of coccolithophores during spring in a temperate Shelf Sea (Celtic Sea, April 2015)
Coccolithophores are key components of phytoplankton communities, exerting a critical impact on the global carbon cycle and the Earthâs climate through the production of coccoliths made of calcium carbonate (calcite) and bioactive gases. Microzooplankton grazing is an important mortality factor in coccolithophore blooms, however little is currently known regarding the mortality (or growth) rates within non-bloom populations. Measurements of coccolithophore calcite production (CP) and dilution experiments to determine microzooplankton (â¤63âŻÂľm) grazing rates were made during a spring cruise (April 2015) at the Central Celtic Sea (CCS), shelf edge (CS2), and within an adjacent April bloom of the coccolithophore Emiliania huxleyi at station J2.
CP at CCS ranged from 10.4 to 40.4âŻÂľmol C mâ3 dâ1 and peaked at the height of the spring phytoplankton bloom (peak chlorophyll-a concentrations âź6âŻmgâŻmâ3). Cell normalised calcification rates declined from âź1.7 to âź0.2âŻpmol C cellâ1 dâ1, accompanied by a shift from a mixed coccolithophore species community to one dominated by the more lightly calcified species E. huxleyi and Calciopappus caudatus. At the CCS, coccolithophore abundance increased from 6 to 94 cells mLâ1, with net growth rates ranging from 0.06 to 0.21 dâ1 from the 4th to the 28th April. Estimates of intrinsic growth and grazing rates from dilution experiments, at the CCS ranged from 0.01 to 0.86 dâ1 and from 0.01 to 1.32 dâ1, respectively, which resulted in variable net growth rates during April. Microzooplankton grazers consumed 59 to >100% of daily calcite production at the CCS. Within the E. huxleyi bloom a maximum density of 1986 cells mLâ1 was recorded, along with CP rates of 6000âŻÂľmol C mâ3 dâ1 and an intrinsic growth rate of 0.29 dâ1, with âź80% of daily calcite production being consumed.
Our results show that microzooplankton can exert strong top-down control on both bloom and non-bloom coccolithophore populations, grazing over 60% of daily growth (and calcite production). The fate of consumed calcite is unclear, but may be lost either through dissolution in acidic food vacuoles, and subsequent release as CO2, or export to the seabed after incorporation into small faecal pellets. With such high microzooplankton-mediated mortality losses, the fate of grazed calcite is clearly a high priority research direction
Search for a W' boson decaying to a bottom quark and a top quark in pp collisions at sqrt(s) = 7 TeV
Results are presented from a search for a W' boson using a dataset
corresponding to 5.0 inverse femtobarns of integrated luminosity collected
during 2011 by the CMS experiment at the LHC in pp collisions at sqrt(s)=7 TeV.
The W' boson is modeled as a heavy W boson, but different scenarios for the
couplings to fermions are considered, involving both left-handed and
right-handed chiral projections of the fermions, as well as an arbitrary
mixture of the two. The search is performed in the decay channel W' to t b,
leading to a final state signature with a single lepton (e, mu), missing
transverse energy, and jets, at least one of which is tagged as a b-jet. A W'
boson that couples to fermions with the same coupling constant as the W, but to
the right-handed rather than left-handed chiral projections, is excluded for
masses below 1.85 TeV at the 95% confidence level. For the first time using LHC
data, constraints on the W' gauge coupling for a set of left- and right-handed
coupling combinations have been placed. These results represent a significant
improvement over previously published limits.Comment: Submitted to Physics Letters B. Replaced with version publishe
Search for the standard model Higgs boson decaying into two photons in pp collisions at sqrt(s)=7 TeV
A search for a Higgs boson decaying into two photons is described. The
analysis is performed using a dataset recorded by the CMS experiment at the LHC
from pp collisions at a centre-of-mass energy of 7 TeV, which corresponds to an
integrated luminosity of 4.8 inverse femtobarns. Limits are set on the cross
section of the standard model Higgs boson decaying to two photons. The expected
exclusion limit at 95% confidence level is between 1.4 and 2.4 times the
standard model cross section in the mass range between 110 and 150 GeV. The
analysis of the data excludes, at 95% confidence level, the standard model
Higgs boson decaying into two photons in the mass range 128 to 132 GeV. The
largest excess of events above the expected standard model background is
observed for a Higgs boson mass hypothesis of 124 GeV with a local significance
of 3.1 sigma. The global significance of observing an excess with a local
significance greater than 3.1 sigma anywhere in the search range 110-150 GeV is
estimated to be 1.8 sigma. More data are required to ascertain the origin of
this excess.Comment: Submitted to Physics Letters
Measurement of the top pair production cross section in 8 TeV proton-proton collisions using kinematic information in the lepton plus jets final state with ATLAS
A measurement is presented of the inclusive production
cross-section in collisions at a center-of-mass energy of TeV
using data collected by the ATLAS detector at the CERN Large Hadron Collider.
The measurement was performed in the lepton+jets final state using a data set
corresponding to an integrated luminosity of 20.3 fb. The cross-section
was obtained using a likelihood discriminant fit and -jet identification was
used to improve the signal-to-background ratio. The inclusive
production cross-section was measured to be
pb assuming a top-quark mass of 172.5 GeV, in good agreement with the
theoretical prediction of pb. The production cross-section in the fiducial region
determined by the detector acceptance is also reported.Comment: Published version, 19 pages plus author list (35 pages total), 3
figures, 2 tables, all figures including auxiliary figures are available at
http://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/TOPQ-2013-06
Measurement of the Lambda(b) cross section and the anti-Lambda(b) to Lambda(b) ratio with Lambda(b) to J/Psi Lambda decays in pp collisions at sqrt(s) = 7 TeV
The Lambda(b) differential production cross section and the cross section
ratio anti-Lambda(b)/Lambda(b) are measured as functions of transverse momentum
pt(Lambda(b)) and rapidity abs(y(Lambda(b))) in pp collisions at sqrt(s) = 7
TeV using data collected by the CMS experiment at the LHC. The measurements are
based on Lambda(b) decays reconstructed in the exclusive final state J/Psi
Lambda, with the subsequent decays J/Psi to an opposite-sign muon pair and
Lambda to proton pion, using a data sample corresponding to an integrated
luminosity of 1.9 inverse femtobarns. The product of the cross section times
the branching ratio for Lambda(b) to J/Psi Lambda versus pt(Lambda(b)) falls
faster than that of b mesons. The measured value of the cross section times the
branching ratio for pt(Lambda(b)) > 10 GeV and abs(y(Lambda(b))) < 2.0 is 1.06
+/- 0.06 +/- 0.12 nb, and the integrated cross section ratio for
anti-Lambda(b)/Lambda(b) is 1.02 +/- 0.07 +/- 0.09, where the uncertainties are
statistical and systematic, respectively.Comment: Submitted to Physics Letters
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