350 research outputs found
Large-scale magnetic fields from inflation in dilaton electromagnetism
The generation of large-scale magnetic fields is studied in dilaton
electromagnetism in inflationary cosmology, taking into account the dilaton's
evolution throughout inflation and reheating until it is stabilized with
possible entropy production. It is shown that large-scale magnetic fields with
observationally interesting strength at the present time could be generated if
the conformal invariance of the Maxwell theory is broken through the coupling
between the dilaton and electromagnetic fields in such a way that the resultant
quantum fluctuations in the magnetic field has a nearly scale-invariant
spectrum. If this condition is met, the amplitude of the generated magnetic
field could be sufficiently large even in the case huge amount of entropy is
produced with the dilution factor as the dilaton decays.Comment: 28 pages, 5 figures, the version accepted for publication in Phys.
Rev. D; some references are adde
Experimental Probes of Localized Gravity: On and Off the Wall
The phenomenology of the Randall-Sundrum model of localized gravity is
analyzed in detail for the two scenarios where the Standard Model (SM) gauge
and matter fields are either confined to a TeV scale 3-brane or may propagate
in a slice of five dimensional anti-deSitter space. In the latter instance, we
derive the interactions of the graviton, gauge, and fermion Kaluza-Klein (KK)
states. The resulting phenomenological signatures are shown to be highly
dependent on the value of the 5-dimensional fermion mass and differ
substantially from the case where the SM fields lie on the TeV-brane. In both
scenarios, we examine the collider signatures for direct production of the
graviton and gauge KK towers as well as their induced contributions to
precision electroweak observables. These direct and indirect signatures are
found to play a complementary role in the exploration of the model parameter
space. In the case where the SM field content resides on the TeV-brane, we show
that the LHC can probe the full parameter space and hence will either discover
or exclude this model if the scale of electroweak physics on the 3-brane is
less than 10 TeV. We also show that spontaneous electroweak symmetry breaking
of the SM must take place on the TeV-brane.Comment: 62 pages, Latex, 22 figure
Large-scale magnetic fields from inflation due to a -even Chern-Simons-like term with Kalb-Ramond and scalar fields
We investigate the generation of large-scale magnetic fields due to the
breaking of the conformal invariance in the electromagnetic field through the
-even dimension-six Chern-Simons-like effective interaction with a fermion
current by taking account of the dynamical Kalb-Ramond and scalar fields in
inflationary cosmology. It is explicitly demonstrated that the magnetic fields
on 1Mpc scale with the field strength of G at the present time
can be induced.Comment: 18 pages, 6 figures, version accepted for publication in Eur. Phys.
J.
Measurement of the ttbar Production Cross Section in ppbar Collisions at sqrt{s} = 1.96 TeV using Kinematic Characteristics of Lepton + Jets Events
We present a measurement of the top quark pair ttbar production cross section
in ppbar collisions at a center-of-mass energy of 1.96 TeV using 230 pb**{-1}
of data collected by the DO detector at the Fermilab Tevatron Collider. We
select events with one charged lepton (electron or muon), large missing
transverse energy, and at least four jets, and extract the ttbar content of the
sample based on the kinematic characteristics of the events. For a top quark
mass of 175 GeV, we measure sigma(ttbar) = 6.7 {+1.4-1.3} (stat) {+1.6- 1.1}
(syst) +/-0.4 (lumi) pb, in good agreement with the standard model prediction.Comment: submitted to Phys.Rev.Let
Measurement of the Isolated Photon Cross Section in p-pbar Collisions at sqrt{s}=1.96 TeV
The cross section for the inclusive production of isolated photons has been
measured in p anti-p collisions at sqrt{s}=1.96 TeV with the D0 detector at the
Fermilab Tevatron Collider. The photons span transverse momenta 23 to 300 GeV
and have pseudorapidity |eta|<0.9. The cross section is compared with the
results from two next-to-leading order perturbative QCD calculations. The
theoretical predictions agree with the measurement within uncertainties.Comment: 7 pages, 5 figures, submitted to Phys.Lett.
Measurement of the p-pbar -> Wgamma + X cross section at sqrt(s) = 1.96 TeV and WWgamma anomalous coupling limits
The WWgamma triple gauge boson coupling parameters are studied using p-pbar
-> l nu gamma + X (l = e,mu) events at sqrt(s) = 1.96 TeV. The data were
collected with the DO detector from an integrated luminosity of 162 pb^{-1}
delivered by the Fermilab Tevatron Collider. The cross section times branching
fraction for p-pbar -> W(gamma) + X -> l nu gamma + X with E_T^{gamma} > 8 GeV
and Delta R_{l gamma} > 0.7 is 14.8 +/- 1.6 (stat) +/- 1.0 (syst) +/- 1.0 (lum)
pb. The one-dimensional 95% confidence level limits on anomalous couplings are
-0.88 < Delta kappa_{gamma} < 0.96 and -0.20 < lambda_{gamma} < 0.20.Comment: Submitted to Phys. Rev. D Rapid Communication
Measurement of the ttbar Production Cross Section in ppbar Collisions at sqrt(s)=1.96 TeV using Lepton + Jets Events with Lifetime b-tagging
We present a measurement of the top quark pair () production cross
section () in collisions at TeV
using 230 pb of data collected by the D0 experiment at the Fermilab
Tevatron Collider. We select events with one charged lepton (electron or muon),
missing transverse energy, and jets in the final state. We employ
lifetime-based b-jet identification techniques to further enhance the
purity of the selected sample. For a top quark mass of 175 GeV, we
measure pb, in
agreement with the standard model expectation.Comment: 7 pages, 2 figures, 3 tables Submitted to Phys.Rev.Let
Measurement of the ratios of the Z/G* + >= n jet production cross sections to the total inclusive Z/G* cross section in ppbar collisions at sqrt(s) = 1.96 TeV
We present a study of events with Z bosons and jets produced at the Fermilab
Tevatron Collider in ppbar collisions at a center of mass energy of 1.96 TeV.
The data sample consists of nearly 14,000 Z/G* -> e+e- candidates corresponding
to the integrated luminosity of 0.4 fb-1 collected using the D0 detector.
Ratios of the Z/G* + >= n jet cross sections to the total inclusive Z/G* cross
section have been measured for n = 1 to 4 jet events. Our measurements are
found to be in good agreement with a next-to-leading order QCD calculation and
with a tree-level QCD prediction with parton shower simulation and
hadronization.Comment: 7 pages, 2 figures, slightly modified, submitted to Phys. Lett.
Search for single top quark production in ppbar collisions at sqrt(s)=1.96 TeV
We present a search for electroweak production of single top quarks in the
s-channel and t-channel using neural networks for signal-background separation.
We have analyzed 230 pb of data collected with the D0 detector at the
Fermilab Tevatron Collider at a center-of-mass energy of 1.96 TeV and find no
evidence for a single top quark signal. The resulting 95% confidence level
upper limits on the single top quark production cross sections are 6.4 pb in
the s-channel and 5.0 pb in the t-channel.Comment: 9 pages, 4 figure
Measurement of B(t->Wb)/B(t->Wq) at sqrt(s) = 1.96 TeV
We present the measurement of R = B(t->Wb)/B(t->Wq) in ppbar collisions at
sqrt(s) = 1.96 TeV, using 230 pb-1 of data collected by the DO experiment at
the Fermilab Tevatron Collider. We fit simultaneously R and the number of
selected top quark pairs (ttbar), to the number of identified b-quark jets in
events with one electron or one muon, three or more jets, and high transverse
energy imbalance. To improve sensitivity, kinematical properties of events with
no identified b-quark jets are included in the fit. We measure R = 1.03 +0.19
-0.17 (stat+syst), in good agreement with the standard model. We set lower
limits of R > 0.61 and |V_tb| > 0.78 at 95% confidence level.Comment: 7 pages, 1 figure submitted to Phys. Rev. Let
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