168 research outputs found
Angle-resolved photoemission in doped charge-transfer Mott insulators
A theory of angle-resolved photoemission (ARPES) in doped cuprates and other
charge-transfer Mott insulators is developed taking into account the realistic
(LDA+U) band structure, (bi)polaron formation due to the strong electron-phonon
interaction, and a random field potential. In most of these materials the first
band to be doped is the oxygen band inside the Mott-Hubbard gap. We derive the
coherent part of the ARPES spectra with the oxygen hole spectral function
calculated in the non-crossing (ladder) approximation and with the exact
spectral function of a one-dimensional hole in a random potential. Some unusual
features of ARPES including the polarisation dependence and spectral shape in
YBa2Cu3O7 and YBa2Cu4O8 are described without any Fermi-surface, large or
small. The theory is compatible with the doping dependence of kinetic and
thermodynamic properties of cuprates as well as with the d-wave symmetry of the
superconducting order parameter.Comment: 8 pages (RevTeX), 10 figures, submitted to Phys. Rev.
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 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
Search for new physics in events with opposite-sign leptons, jets, and missing transverse energy in pp collisions at sqrt(s) = 7 TeV
A search is presented for physics beyond the standard model (BSM) in final
states with a pair of opposite-sign isolated leptons accompanied by jets and
missing transverse energy. The search uses LHC data recorded at a
center-of-mass energy sqrt(s) = 7 TeV with the CMS detector, corresponding to
an integrated luminosity of approximately 5 inverse femtobarns. Two
complementary search strategies are employed. The first probes models with a
specific dilepton production mechanism that leads to a characteristic kinematic
edge in the dilepton mass distribution. The second strategy probes models of
dilepton production with heavy, colored objects that decay to final states
including invisible particles, leading to very large hadronic activity and
missing transverse energy. No evidence for an event yield in excess of the
standard model expectations is found. Upper limits on the BSM contributions to
the signal regions are deduced from the results, which are used to exclude a
region of the parameter space of the constrained minimal supersymmetric
extension of the standard model. Additional information related to detector
efficiencies and response is provided to allow testing specific models of BSM
physics not considered in this paper.Comment: Replaced with published version. Added journal reference and DO
Measurement of isolated photon production in pp and PbPb collisions at sqrt(sNN) = 2.76 TeV
Isolated photon production is measured in proton-proton and lead-lead
collisions at nucleon-nucleon centre-of-mass energies of 2.76 TeV in the
pseudorapidity range |eta|<1.44 and transverse energies ET between 20 and 80
GeV with the CMS detector at the LHC. The measured ET spectra are found to be
in good agreement with next-to-leading-order perturbative QCD predictions. The
ratio of PbPb to pp isolated photon ET-differential yields, scaled by the
number of incoherent nucleon-nucleon collisions, is consistent with unity for
all PbPb reaction centralities.Comment: Submitted to Physics Letters
Evolutionary origins of the estrogen signaling system : insights from amphioxus
Author Posting. Š The Author(s), 2011. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Journal of Steroid Biochemistry and Molecular Biology 127 (2011): 176â188, doi:10.1016/j.jsbmb.2011.03.022.Classically, the estrogen signaling system has two core components: cytochrome P450
aromatase (CYP19), the enzyme complex that catalyzes the rate limiting step in estrogen
biosynthesis; and estrogen receptors (ERs), ligand activated transcription factors that interact
with the regulatory region of target genes to mediate the biological effects of estrogen. While the
importance of estrogens for regulation of reproduction, development and physiology has been
well-documented in gnathostome vertebrates, the evolutionary origins of estrogen as a hormone
are still unclear. As invertebrates within the phylum Chordata, cephalochordates (e.g. the
amphioxus of the genus Branchiostoma) are among the closest invertebrate relatives of the
vertebrates and can provide critical insight into the evolution of vertebrate-specific molecules
and pathways. To address this question, this paper briefly reviews relevant earlier studies that
help to illuminate the history of the aromatase and ER genes, with a particular emphasis on
insights from amphioxus and other invertebrates. We then present new analyses of amphioxus
aromatase and ER sequence and function, including an in silico model of the amphioxus
aromatase protein, and CYP19 gene analysis. CYP19 shares a conserved gene structure with
vertebrates (9 coding exons) and moderate sequence conservation (40% amino acid identity with
human CYP19). Modeling of the amphioxus aromatase substrate binding site and simulated
docking of androstenedione in comparison to the human aromatase shows that the substrate
binding site is conserved and predicts that androstenedione could be a substrate for amphioxus
CYP19. The amphioxus ER is structurally similar to vertebrate ERs, but differs in sequence and
key residues of the ligand binding domain. Consistent with results from other laboratories,
amphioxus ER did not bind radiolabeled estradiol, nor did it modulate gene expression on an estrogen-responsive element (ERE) in the presence 59 of estradiol, 4-hydroxytamoxifen,
diethylstilbestrol, bisphenol A or genistein. Interestingly, it has been shown that a related gene,
the amphioxus âsteroid receptorâ (SR), can be activated by estrogens and that amphioxus ER can
repress this activation. CYP19, ER and SR are all primarily expressed in gonadal tissue,
suggesting an ancient paracrine/autocrinesignaling role, but it is not yet known how their
expression is regulated and, if estrogen is actually synthesized in amphioxus, whether it has a
role in mediating any biological effects . Functional studies are clearly needed to link emerging
bioinformatics and in vitro molecular biology results with organismal physiology to develop an
understanding of the evolution of estrogen signaling.Supported by grants from the NIEHS P42 ES07381 (GVC, SV) and EPA (STAR-RD831301)
(GVC), a Ruth L Kirschstein National Research Service Award (AT, F32 ES013092-01), an NIH
traineeship (SS, SG), a NATO Fellowship (AN) and the Boston University Undergraduate
Research Program (LC)
Measurement of the mass difference between top quark and antiquark in pp collisions at root s=8 TeV
Peer reviewe
Global, regional, and national comparative risk assessment of 79 behavioural, environmental and occupational, and metabolic risks or clusters of risks, 1990-2015: A systematic analysis for the Global Burden of Disease Study 2015
Background: The Global Burden of Diseases, Injuries, and Risk Factors Study 2015 provides an up-to-date synthesis of the evidence for risk factor exposure and the attributable burden of disease. By providing national and subnational assessments spanning the past 25 years, this study can inform debates on the importance of addressing risks in context.
Methods: We used the comparative risk assessment framework developed for previous iterations of the Global Burden of Disease Study to estimate attributable deaths, disability-adjusted life-years (DALYs), and trends in exposure by age group, sex, year, and geography for 79 behavioural, environmental and occupational, and metabolic risks or clusters of risks from 1990 to 2015. This study included 388 risk-outcome pairs that met World Cancer Research Fund-defined criteria for convincing or probable evidence. We extracted relative risk and exposure estimates from randomised controlled trials, cohorts, pooled cohorts, household surveys, census data, satellite data, and other sources. We used statistical models to pool data, adjust for bias, and incorporate covariates. We developed a metric that allows comparisons of exposure across risk factorsâthe summary exposure value. Using the counterfactual scenario of theoretical minimum risk level, we estimated the portion of deaths and DALYs that could be attributed to a given risk. We decomposed trends in attributable burden into contributions from population growth, population age structure, risk exposure, and risk-deleted cause-specific DALY rates. We characterised risk exposure in relation to a Socio-demographic Index (SDI).
Findings: Between 1990 and 2015, global exposure to unsafe sanitation, household air pollution, childhood underweight, childhood stunting, and smoking each decreased by more than 25%. Global exposure for several occupational risks, high body-mass index (BMI), and drug use increased by more than 25% over the same period. All risks jointly evaluated in 2015 accounted for 57¡8% (95% CI 56¡6â58¡8) of global deaths and 41¡2% (39¡8â42¡8) of DALYs. In 2015, the ten largest contributors to global DALYs among Level 3 risks were high systolic blood pressure (211¡8 million [192¡7 million to 231¡1 million] global DALYs), smoking (148¡6 million [134¡2 million to 163¡1 million]), high fasting plasma glucose (143¡1 million [125¡1 million to 163¡5 million]), high BMI (120¡1 million [83¡8 million to 158¡4 million]), childhood undernutrition (113¡3 million [103¡9 million to 123¡4 million]), ambient particulate matter (103¡1 million [90¡8 million to 115¡1 million]), high total cholesterol (88¡7 million [74¡6 million to 105¡7 million]), household air pollution (85¡6 million [66¡7 million to 106¡1 million]), alcohol use (85¡0 million [77¡2 million to 93¡0 million]), and diets high in sodium (83¡0 million [49¡3 million to 127¡5 million]). From 1990 to 2015, attributable DALYs declined for micronutrient deficiencies, childhood undernutrition, unsafe sanitation and water, and household air pollution; reductions in risk-deleted DALY rates rather than reductions in exposure drove these declines. Rising exposure contributed to notable increases in attributable DALYs from high BMI, high fasting plasma glucose, occupational carcinogens, and drug use. Environmental risks and childhood undernutrition declined steadily with SDI; low physical activity, high BMI, and high fasting plasma glucose increased with SDI. In 119 countries, metabolic risks, such as high BMI and fasting plasma glucose, contributed the most attributable DALYs in 2015. Regionally, smoking still ranked among the leading five risk factors for attributable DALYs in 109 countries; childhood underweight and unsafe sex remained primary drivers of early death and disability in much of sub-Saharan Africa.
Interpretation: Declines in some key environmental risks have contributed to declines in critical infectious diseases. Some risks appear to be invariant to SDI. Increasing risks, including high BMI, high fasting plasma glucose, drug use, and some occupational exposures, contribute to rising burden from some conditions, but also provide opportunities for intervention. Some highly preventable risks, such as smoking, remain major causes of attributable DALYs, even as exposure is declining. Public policy makers need to pay attention to the risks that are increasingly major contributors to global burden.
Funding: Bill & Melinda Gates Foundation
Studies of jet quenching using isolated-photon + jet correlations in PbPb and pp collisions at sqrt(s[NN]) = 2.76 TeV
Results from the first study of isolated-photon + jet correlations in
relativistic heavy ion collisions are reported. The analysis uses data from
PbPb collisions at a centre-of-mass energy of 2.76 TeV per nucleon pair
corresponding to an integrated luminosity of 150 inverse microbarns recorded by
the CMS experiment at the LHC. For events containing an isolated photon with
transverse momentum pt(gamma) > 60 GeV and an associated jet with pt(Jet) > 30
GeV, the photon + jet pt imbalance is studied as a function of collision
centrality and compared to pp data and PYTHIA calculations at the same
collision energy. Using the pt(gamma) of the isolated photon as an estimate of
the momentum of the associated parton at production, this measurement allows an
unbiased characterisation of the in-medium parton energy loss. For more central
PbPb collisions, a significant decrease in the ratio pt(Jet)/pt(gamma) relative
to that in the PYTHIA reference is observed. Furthermore, significantly more
pt(gamma) > 60 GeV photons in PbPb are observed not to have an associated
pt(Jet) > 30 GeV jet, compared to the reference. However, no significant
broadening of the photon + jet azimuthal correlation is observed.Comment: Submitted to Physics Letters
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