576 research outputs found
On relativization of the Sommerfeld-Gamow-Sakharov factor
The Sommerfeld-Gamow-Sakharov factor is considered for the general case of
arbitrary masses and energies. It is shown that the scalar triangular one-loop
diagram gives the Coulomb singularity in radiative corrections at the
threshold. The singular part of the correction is factorized at the complete
Born cross section regardless of its partial wave decomposition. Different
approaches to generalize the factor are discussed.Comment: 9 pages, 4 figures; references and discussion are extende
NLO QCD corrections to off-shell top-antitop production with leptonic decays at hadron colliders
We present details of a calculation of the cross section for hadronic
top-antitop production in next-to-leading order (NLO) QCD, including the decays
of the top and antitop into bottom quarks and leptons. This calculation is
based on matrix elements for \nu e e+ \mu- \bar{\nu}_{\mu}b\bar{b} production
and includes all non-resonant diagrams, interferences, and off-shell effects of
the top quarks. Such contributions are formally suppressed by the top-quark
width and turn out to be small in the inclusive cross section. However, they
can be strongly enhanced in exclusive observables that play an important role
in Higgs and new-physics searches. Also non-resonant and off-shell effects due
to the finite W-boson width are investigated in detail, but their impact is
much smaller than naively expected. We also introduce a matching approach to
improve NLO calculations involving intermediate unstable particles. Using a
fixed QCD scale leads to perturbative instabilities in the high-energy tails of
distributions, but an appropriate dynamical scale stabilises NLO predictions.
Numerical results for the total cross section, several distributions, and
asymmetries are presented for Tevatron and the LHC at 7 TeV, 8 TeV, and 14 TeV.Comment: 61 pp. Matches version published in JHEP; one more reference adde
Electroweak corrections to W-boson pair production at the LHC
Vector-boson pair production ranks among the most important Standard-Model
benchmark processes at the LHC, not only in view of on-going Higgs analyses.
These processes may also help to gain a deeper understanding of the electroweak
interaction in general, and to test the validity of the Standard Model at
highest energies. In this work, the first calculation of the full one-loop
electroweak corrections to on-shell W-boson pair production at hadron colliders
is presented. We discuss the impact of the corrections on the total cross
section as well as on relevant differential distributions. We observe that
corrections due to photon-induced channels can be amazingly large at energies
accessible at the LHC, while radiation of additional massive vector bosons does
not influence the results significantly.Comment: 29 pages, 15 figures, 4 tables; some references and comments on
\gamma\gamma -> WW added; matches version published in JHE
A Comprehensive Analysis of Electric Dipole Moment Constraints on CP-violating Phases in the MSSM
We analyze the constraints placed on individual, flavor diagonal CP-violating
phases in the minimal supersymmetric extension of the Standard Model (MSSM) by
current experimental bounds on the electric dipole moments (EDMs) of the
neutron, Thallium, and Mercury atoms. We identify the four CP-violating phases
that are individually highly constrained by current EDM bounds, and we explore
how these phases and correlations among them are constrained by current EDM
limits. We also analyze the prospective implications of the next generation of
EDM experiments. We point out that all other CP-violating phases in the MSSM
are not nearly as tightly constrained by limits on the size of EDMs. We
emphasize that a rich set of phenomenological consequences is potentially
associated with these generically large EDM-allowed phases, ranging from B
physics, electroweak baryogenesis, and signals of CP-violation at the CERN
Large Hadron Collider and at future linear colliders. Our numerical study takes
into account the complete set of contributions from one- and two-loop EDMs of
the electron and quarks, one- and two-loop Chromo-EDMs of quarks, the Weinberg
3-gluon operator, and dominant 4-fermion CP-odd operator contributions,
including contributions which are both included and not included yet in the
CPsuperH2.0 package. We also introduce an open-source numerical package, 2LEDM,
which provides the complete set of two-loop electroweak diagrams contributing
to the electric dipole moments of leptons and quarks.Comment: 23 pages, 11 figures; v2: references added, minor change
Limits on WWZ and WW\gamma couplings from p\bar{p}\to e\nu jj X events at \sqrt{s} = 1.8 TeV
We present limits on anomalous WWZ and WW-gamma couplings from a search for
WW and WZ production in p-bar p collisions at sqrt(s)=1.8 TeV. We use p-bar p
-> e-nu jjX events recorded with the D0 detector at the Fermilab Tevatron
Collider during the 1992-1995 run. The data sample corresponds to an integrated
luminosity of 96.0+-5.1 pb^(-1). Assuming identical WWZ and WW-gamma coupling
parameters, the 95% CL limits on the CP-conserving couplings are
-0.33<lambda<0.36 (Delta-kappa=0) and -0.43<Delta-kappa<0.59 (lambda=0), for a
form factor scale Lambda = 2.0 TeV. Limits based on other assumptions are also
presented.Comment: 11 pages, 2 figures, 2 table
Synergistic Association of PTGS2 and CYP2E1 Genetic Polymorphisms with Lung Cancer Risk in Northeastern Chinese
BACKGROUND: Lung cancer is the most common cause of cancer-related deaths worldwide. The aim of this study was to investigate the association of five extensively-studied polymorphisms in PTGS2 (rs689466, rs5275, rs20417) and CYP2E1 (rs2031920, rs6413432) genes with lung cancer risk in a large northeastern Chinese population. METHODOLOGY/PRINCIPAL FINDINGS: This is a hospital-based case-control study involving 684 patients with lung cancer and 604 cancer-free controls. Genotyping was performed using the PCR-LDR method. Data were analyzed using Haplo.stats and MDR programs. There were significant differences between patients and controls in allele/genotype distributions of rs5275 (P = 0.002/0.003) and rs6413432 (P = 0.037/0.044), as well as in genotype distributions of rs689466 (P = 0.02). The risk for lung cancer associated with the rs5275-C mutant allele was decreased by 60% (95% CI [confidence interval]: 0.21-0.74; P = 0.004) under the recessive model. Carriers of rs689466-G mutant allele had a 28% (95% CI: 0.57-0.92; P = 0.008) reduced risk of developing lung cancer relative to the AA genotype carriers. In haplotype analysis, haplotype G-C-C-T (in order of rs689466, rs5275, rs2031920 and rs6413432) decreased the odds of lung cancer by 28% (95% CI: 0.51-0.93; P = 0.019) after adjusting for confounding factors, whereas haplotype A-T-T-T had 1.49-fold (95% CI: 1.21-1.79; P = 0.012) increased risk for lung cancer. Using MDR method, the overall best model including rs5275, rs689466 and rs6413432 polymorphisms was identified with a maximal testing accuracy of 66.1% and a maximal cross-validation consistency of 10 out of 10 (P = 0.003). CONCLUSIONS/SIGNIFICANCE: Our findings demonstrated a potentially synergistic association of PTGS2 and CYP2E1 polymorphisms with the underlying cause of lung cancer in northeastern Chinese
A historical reflection on the discovery of human retroviruses
The discovery of HIV-1 as the cause of AIDS was one of the major scientific achievements during the last century. Here the events leading to this discovery are reviewed with particular attention to priority and actual contributions by those involved. Since I would argue that discovering HIV was dependent on the previous discovery of the first human retrovirus HTLV-I, the history of this discovery is also re-examined. The first human retroviruses (HTLV-I) was first reported by Robert C. Gallo and coworkers in 1980 and reconfirmed by Yorio Hinuma and coworkers in 1981. These discoveries were in turn dependent on the previous discovery by Gallo and coworkers in 1976 of interleukin 2 or T-cell growth factor as it was called then. HTLV-II was described by Gallo's group in 1982. A human retrovirus distinct from HTLV-I and HTLV-II in that it was shown to have the morphology of a lentivirus was in my mind described for the first time by Luc Montagnier in an oral presentation at Cold Spring Harbor in September of 1983. This virus was isolated from a patient with lymphadenopathy using the protocol previously described for HTLV by Gallo. The first peer reviewed paper by Montagnier's group of such a retrovirus, isolated from two siblings of whom one with AIDS, appeared in Lancet in April of 1984. However, the proof that a new human retrovirus (HIV-1) was the cause of AIDS was first established in four publications by Gallo's group in the May 4th issue of Science in 1984
Search for New Physics in e mu X Data at D0 Using Sleuth: A Quasi-Model-Independent Search Strategy for New Physics
We present a quasi-model-independent search for the physics responsible for
electroweak symmetry breaking. We define final states to be studied, and
construct a rule that identifies a set of relevant variables for any particular
final state. A new algorithm ("Sleuth") searches for regions of excess in those
variables and quantifies the significance of any detected excess. After
demonstrating the sensitivity of the method, we apply it to the semi-inclusive
channel e mu X collected in 108 pb^-1 of ppbar collisions at sqrt(s) = 1.8 TeV
at the D0 experiment during 1992-1996 at the Fermilab Tevatron. We find no
evidence of new high p_T physics in this sample.Comment: 23 pages, 12 figures. Submitted to Physical Review
The Dijet Mass Spectrum and a Search for Quark Compositeness in bar{p}p Collisions at sqrt{s} = 1.8 TeV
Using the DZero detector at the 1.8 TeV pbarp Fermilab Tevatron collider, we
have measured the inclusive dijet mass spectrum in the central pseudorapidity
region |eta_jet| < 1.0 for dijet masses greater than 200 Gev/c^2. We have also
measured the ratio of spectra sigma(|eta_jet| < 0.5)/sigma(0.5 < |eta_jet| <
1.0). The order alpha_s^3 QCD predictions are in good agreement with the data
and we rule out models of quark compositeness with a contact interaction scale
< 2.4 TeV at the 95% confidence level.Comment: 11 pages, 4 figures, 2 tables, submitted to Phys. Rev. Let
Search For Heavy Pointlike Dirac Monopoles
We have searched for central production of a pair of photons with high
transverse energies in collisions at TeV using of data collected with the D\O detector at the Fermilab Tevatron in
1994--1996. If they exist, virtual heavy pointlike Dirac monopoles could
rescatter pairs of nearly real photons into this final state via a box diagram.
We observe no excess of events above background, and set lower 95% C.L. limits
of on the mass of a spin 0, 1/2, or 1 Dirac
monopole.Comment: 12 pages, 4 figure
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