497 research outputs found
Crossing the cosmological constant line in a dilatonic brane-world model with and without curvature corrections
We construct a new brane-world model composed of a bulk -with a dilatonic
field-, plus a brane -with brane tension coupled to the dilaton-, cold dark
matter and an induced gravity term. It is possible to show that depending on
the nature of the coupling between the brane tension and the dilaton this model
can describe the late-time acceleration of the brane expansion (for the normal
branch) as it moves within the bulk. The acceleration is produced together with
a mimicry of the crossing of the cosmological constant line (w=-1) on the
brane, although this crossing of the phantom divide is obtained without
invoking any phantom matter neither on the brane nor in the bulk. The role of
dark energy is played by the brane tension, which reaches a maximum positive
value along the cosmological expansion of the brane. It is precisely at that
maximum that the crossing of the phantom divide takes place. We also show that
these results remain valid when the induced gravity term on the brane is
switched off.Comment: 12 pages, 2 figures, RevTeX
Metastability of (d+n)-dimensional elastic manifolds
We investigate the depinning of a massive elastic manifold with internal
dimensions, embedded in a -dimensional space, and subject to an
isotropic pinning potential The tunneling process is
driven by a small external force We find the zero temperature and
high temperature instantons and show that for the case the
problem exhibits a sharp transition from quantum to classical behavior: At low
temperatures the Euclidean action is constant up to exponentially
small corrections, while for The results are universal and do not depend on the detailed shape
of the trapping potential . Possible applications of the problem to
the depinning of vortices in high- superconductors and nucleation in
-dimensional phase transitions are discussed. In addition, we determine the
high-temperature asymptotics of the preexponential factor for the
-dimensional problem.Comment: RevTeX, 10 pages, 3 figures inserte
Higher order QCD predictions for associated Higgs production with anomalous couplings to gauge bosons
We present predictions for the associated production of a Higgs boson at NLO+PS accuracy, including the effect of anomalous interactions between the Higgs and gauge bosons. We present our results in different frameworks, one in which the interaction vertex between the Higgs boson and Standard Model W and Z bosons is parameterized in terms of general Lorentz structures, and one in which Electroweak symmetry breaking is manifestly linear and the resulting operators arise through a six-dimensional effective field theory framework. We present analytic calculations of the Standard Model and Beyond the Standard Model contributions, and discuss the phenomenological impact of the higher order pieces. Our results are implemented in the NLO Monte Carlo program MCFM, and interfaced to shower Monte Carlos through the Powheg box framework
Higgs Physics: Theory
I review the theoretical aspects of the physics of Higgs bosons, focusing on
the elements that are relevant for the production and detection at present
hadron colliders. After briefly summarizing the basics of electroweak symmetry
breaking in the Standard Model, I discuss Higgs production at the LHC and at
the Tevatron, with some focus on the main production mechanism, the gluon-gluon
fusion process, and summarize the main Higgs decay modes and the experimental
detection channels. I then briefly survey the case of the minimal
supersymmetric extension of the Standard Model. In a last section, I review the
prospects for determining the fundamental properties of the Higgs particles
once they have been experimentally observed.Comment: 21 pages, 15 figures. Talk given at the XXV International Symposium
on Lepton Photon Interactions at High Energies (Lepton Photon 11), 22-27
August 2011, Mumbai, Indi
Periodic Bounce for Nucleation Rate at Finite Temperature in Minisuperspace Models
The periodic bounce configurations responsible for quantum tunneling are
obtained explicitly and are extended to the finite energy case for
minisuperspace models of the Universe. As a common feature of the tunneling
models at finite energy considered here we observe that the period of the
bounce increases with energy monotonically. The periodic bounces do not have
bifurcations and make no contribution to the nucleation rate except the one
with zero energy. The sharp first order phase transition from quantum tunneling
to thermal activation is verified with the general criterions.Comment: 17 pages, 5 postscript figures include
NLO QCD+EW predictions for HV and HV +jet production including parton-shower effects
We present the first NLO QCD+EW predictions for Higgs boson production in association with a ℓνℓ or ℓ+ℓ− pair plus zero or one jets at the LHC. Fixed-order NLO QCD+EW calculations are combined with a QCD+QED parton shower using the recently developed resonance-aware method in the POWHEG framework. Moreover, applying the improved MiNLO technique to Hℓνℓ +jet and Hℓ+ℓ− +jet production at NLO QCD+EW, we obtain predictions that are NLO accurate for observables with both zero or one resolved jet. This approach permits also to capture higher-order effects associated with the interplay of EW corrections and QCD radiation. The behavior of EW corrections is studied for various kinematic distributions, relevant for experimental analyses of Higgsstrahlung processes at the 13 TeV LHC. Exact NLO EW corrections are complemented with approximate analytic formulae that account for the leading and next-to-leading Sudakov logarithms in the high-energy regime. In the tails of transverse-momentum distributions, relevant for analyses in the boosted Higgs regime, the Sudakov approximation works well, and NLO EW effects can largely exceed the ten percent level. Our predictions are based on the POWHEG BOX RES+OpenLoops framework in combination with the Pythia 8.1 parton shower
Are smoking and chlamydial infection risk factors for CIN? Different results after adjustment for HPV DNA and antibodies
To identify the risk factors for cervical intraepithelial neoplasia (CIN), we reanalysed the data from our previous case-control study by adjusting for human papillomavirus (HPV) antibodies. Unlike our previous study based only on HPV DNA, smoking and Chlamydia trachomatis infection were revealed as significant risk factors for CIN after adjustment for HPV antibodies
A Step Beyond the Bounce: Bubble Dynamics in Quantum Phase Transitions
We study the dynamical evolution of a phase interface or bubble in the
context of a \lambda \phi^4 + g \phi^6 scalar quantum field theory. We use a
self-consistent mean-field approximation derived from a 2PI effective action to
construct an initial value problem for the expectation value of the quantum
field and two-point function. We solve the equations of motion numerically in
(1+1)-dimensions and compare the results to the purely classical evolution. We
find that the quantum fluctuations dress the classical profile, affecting both
the early time expansion of the bubble and the behavior upon collision with a
neighboring interface.Comment: 12 pages, multiple figure
The fully differential hadronic production of a Higgs boson via bottom quark fusion at NNLO
The fully differential computation of the hadronic production cross section
of a Higgs boson via bottom quarks is presented at NNLO in QCD. Several
differential distributions with their corresponding scale uncertainties are
presented for the 8 TeV LHC. This is the first application of the method of
non-linear mappings for NNLO differential calculations at hadron colliders.Comment: 27 pages, 13 figures, 1 lego plo
Quantum-Classical Transition of the Escape Rate of a Uniaxial Spin System in an Arbitrarily Directed Field
The escape rate \Gamma of the large-spin model described by the Hamiltonian H
= -DS_z^2 - H_zS_z - H_xS_x is investigated with the help of the mapping onto a
particle moving in a double-well potential U(x). The transition-state method
yields in the moderate-damping case as a Boltzmann average of the
quantum transition probabilities. We have shown that the transition from the
classical to quantum regimes with lowering temperature is of the first order
(d\Gamma/dT discontinuous at the transition temperature T_0) for h_x below the
phase boundary line h_x=h_{xc}(h_z), where h_{x,z}\equiv H_{x,z}/(2SD), and of
the second order above this line. In the unbiased case (H_z=0) the result is
h_{xc}(0)=1/4, i.e., one fourth of the metastability boundary h_{xm}=1, at
which the barrier disappears. In the strongly biased limit \delta\equiv 1-h_z
<< 1, one has h_{xc} \cong (2/3)^{3/4}(\sqrt{3}-\sqrt{2})\delta^{3/2}\cong
0.2345 \delta^{3/2}, which is about one half of the boundary value h_{xm} \cong
(2\delta/3)^{3/2} \cong 0.5443 \delta^{3/2}.The latter case is relevant for
experiments on small magnetic particles, where the barrier should be lowered to
achieve measurable quantum escape rates.Comment: 17 PR pages, 16 figures; published versio
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