119277901
Measurement of dijet production in diffractive deep-inelastic scattering with a leading proton at HERA
The cross section of diffractive deep-inelastic scattering ep→eXp is measured, where the system X contains at least two jets and the leading final state proton is detected in the H1 Forward Proton Spectrometer. The measurement is performed for fractional proton longitudinal momentum loss xℙ<0.1 and covers the range 0.1<|t|<0.7 GeV2 in squared four-momentum transfer at the proton vertex and 4<Q2<110 GeV2 in photon virtuality. The differential cross sections extrapolated to |t|<1 GeV2 are in agreement with next-to-leading order QCD predictions based on diffractive parton distribution functions extracted from measurements of inclusive and dijet cross sections in diffractive deep-inelastic scattering. The data are also compared with leading order Monte Carlo models.
119204233
Search for new physics in events with same-sign dileptons and b-tagged jets in pp collisions at $ \sqrt {s} = 7 $ TeV
A bstractA search for new physics is performed using isolated same-sign dileptons with at least two b-quark jets in the final state. Results are based on a 4.98 fb−1 sample of proton-proton collisions at a centre-of-mass energy of 7 TeV collected by the CMS detector. No excess above the standard model background is observed. Upper limits at 95% confidence level are set on the number of events from non-standard-model sources. These limits are used to set constraints on a number of new physics models. Information on acceptance and efficiencies are also provided so that the results can be used to confront additional models in an approximate way.
117033883
Measurement of the single-top-quark t-channel cross section in pp collisions at $ \sqrt{s}=7 $ TeV
A bstractA measurement of the single-top-quark t-channel production cross section in pp collisions at $ \sqrt{s}=7 $ TeV with the CMS detector at the LHC is presented. Two different and complementary approaches have been followed. The first approach exploits the distributions of the pseudorapidity of the recoil jet and reconstructed top-quark mass using background estimates determined from control samples in data. The second approach is based on multivariate analysis techniques that probe the compatibility of the candidate events with the signal. Data have been collected for the muon and electron final states, corresponding to integrated luminosities of 1.17 and 1.56 fb−1, respectively. The single-top-quark production cross section in the t-channel is measured to be 67.2±6.1 pb, in agreement with the approximate next-to-next-to-leading-order standard model prediction. Using the standard model electroweak couplings, the CKM matrix element |Vtb| is measured to be 1.020 ± 0.046 (meas.) ± 0.017 (theor.).
18536190
Search for Excited Electrons in ep Collisions at HERA
A search for excited electrons is performed using the full e±p data sample collected by the H1 experiment at HERA, corresponding to a total luminosity of 475 pb−1. The electroweak decays of excited electrons e*→eγ, e*→eZ and e*→νW with subsequent hadronic or leptonic decays of the W and Z bosons are considered. No evidence for excited electron production is found. Mass dependent exclusion limits on e* production cross sections and on the ratio f/Λ of the coupling to the compositeness scale are derived within gauge mediated models. These limits extend the excluded region compared to previous excited electron searches. The e* production via contact interactions is also addressed for the first time in ep collisions.
122330531
Search for dark matter and large extra dimensions in monojet events in pp collisions at $ \sqrt {s} = {7} $ TeV
A bstractA search has been made for events containing an energetic jet and an imbalance in transverse momentum using a data sample of pp collisions at a center-of-mass energy of 7 TeV. This signature is common to both dark matter and extra dimensions models. The data were collected by the CMS detector at the LHC and correspond to an integrated luminosity of 5.0 fb−1. The number of observed events is consistent with the standard model expectation. Constraints on the dark matter-nucleon scattering cross sections are determined for both spin-independent and spin-dependent interaction models. For the spin-independent model, these are the most constraining limits for a dark matter particle with mass below 3.5 GeV/c2, a region unexplored by direct detection experiments. For the spin-dependent model, these are the most stringent constraints over the 0.1–200 GeV/c2 mass range. The constraints on the Arkani-Hamed, Dimopoulos, and Dvali model parameter MD determined as a function of the number of extra dimensions are also an improvement over the previous results.
36326465
Search for third-generation leptoquarks and scalar bottom quarks in pp collisions at $ \sqrt{s}=7\;TeV $
A bstractResults are presented from a search for third-generation leptoquarks and scalar bottom quarks in a sample of proton-proton collisions at $ \sqrt{s}=7\;TeV $ collected by the CMS experiment at the LHC, corresponding to an integrated luminosity of 4.7 fb−1. A scenario where the new particles are pair produced and each decays to a b quark plus a tau neutrino or neutralino is considered. The number of observed events is found to be in agreement with the standard model prediction. Upper limits are set at 95% confidence level on the production cross sections. Leptoquarks with masses below ~450 GeV are excluded. Upper limits in the mass plane of the scalar quark and neutralino are set such that scalar bottom quark masses up to 410 GeV are excluded for neutralino masses of 50 GeV.
121660706
Cosmological density perturbations with modified gravity
We determine how the usual formula for density perturbations from inflationary cosmology should be modified when the inflaton is coupled to the scalar curvature at the level of the Lagrangian. By applying a conformal transformation to a single gauge invariant quantity, we rederive a previously proposed formula for the fully coupled system in a simple and unambiguous way
119451817
CHAOS IN TIME-DEPENDENT VARIATIONAL APPROXIMATIONS TO QUANTUM DYNAMICS
Dynamical chaos has recently been shown to exist in the Gaussian approximation in quan-tum mechanics and in the self-consistent mean ﬁeld approach to studying the dynamics ofquantum ﬁelds. In this study, we ﬁrst show that any variationalapproximationto the dynam-ics of a quantum system based on the Dirac action principle leads to a classical Hamiltoniandynamics for the variational parameters. Since this Hamiltonian is generically nonlinearand nonintegrable, the dynamics thus generated can be chaotic, in distinction to the exactquantum evolution. We then restrict attention to a system of two biquadratically coupledquantum oscillators and study two variational schemes, the leading order large N (fourcanonical variables) and Hartree (six canonical variables) approximations. The chaos seenin the approximate dynamics is an artifact of the approximations: this is demonstrated bythe fact that its onset occurs on the same characteristic time scale as the breakdown of theapproximations when compared to numerical solutions of the time-dependent Schr¨odingerequation.PACS numbers: 05.45. +b, 03.65. Sq, 2.30 Wd, 03.65 -w
56264578
EXACT THERMODYNAMICS OF THE DOUBLE SINH-GORDON THEORY IN 1 + 1 DIMENSIONS
We study the classical thermodynamics of a (1+1) -dimensional double-well sinh-Gordon theory. Remarkably, the Schr{umlt o}dinger-like equation resulting from the transfer integral method is quasi-exactly solvable at several temperatures. This allows exact calculation of the partition function and some correlation functions above and below the short-range order ({open_quotes}kink{close_quotes}) transition, in striking agreement with high resolution Langevin simulations. Interesting connections with the Landau-Ginzburg and double sine-Gordon models are also established. {copyright} {ital 1997} {ital The American Physical Society}
118588532
The Coyote Universe Extended: Precision Emulation of the Matter Power Spectrum
Modern sky surveys are returning precision measurements of cosmological statistics such as weak lensing shear correlations, the distribution of galaxies, and cluster abundance. To fully exploit these observations, theorists must provide predictions that are at least as accurate as the measurements, as well as robust estimates of systematic errors that are inherent to the modeling process. In the nonlinear regime of structure formation, this challenge can only be overcome by developing a large-scale, multi-physics simulation capability covering a range of cosmological models and astrophysical processes. As a first step to achieving this goal, we have recently developed a prediction scheme for the matter power spectrum (a so-called emulator), accurate at the 1% level out to k ~ 1 Mpc–1 and z = 1 for wCDM cosmologies based on a set of high-accuracy N-body simulations. It is highly desirable to increase the range in both redshift and wavenumber and to extend the reach in cosmological parameter space. To make progress in this direction, while minimizing computational cost, we present a strategy that maximally reuses the original simulations. We demonstrate improvement over the original spatial dynamic range by an order of magnitude, reaching k ~ 10 h Mpc–1, a four-fold increase in redshift coverage, to z = 4, and now include the Hubble parameter as a new independent variable. To further the range in k and z, a new set of nested simulations run at modest cost is added to the original set. The extension in h is performed by including perturbation theory results within a multi-scale procedure for building the emulator. This economical methodology still gives excellent error control, ~5% near the edges of the domain of applicability of the emulator. A public domain code for the new emulator is released as part of the work presented in this paper.
119516986
Nonequilibrium dynamics of symmetry breaking in lambda Phi**4 field theory
The time evolution of O(N) symmetric lambda Phi^4 scalar field theory is studied in the large N limit. In this limit the mean field and two-point correlation function evolve together as a self-consistent closed Hamiltonian system, characterized by a Gaussian density matrix. The static part of the effective Hamiltonian defines the True Effective Potential U_eff for configurations far from thermal equilibrium. Numerically solving the time evolution equations for energy densities corresponding to a quench in the unstable spinodal region, we find results quite different from what might be inferred from the equilibrium free energy ``effective'' potential F. Typical time evolutions show effectively irreversible energy flow from the coherent mean fields to the quantum fluctuating modes, due to the creation of massless Goldstone bosons near threshold. The plasma frequency and collisionless damping rate of the mean fields are calculated in terms of the particle number density by a linear response analysis and compared with the numerical results. Dephasing of the fluctuations leads also to the growth of an effective entropy and the transition from quantum to classical behavior of the ensemble. In addition to casting some light on fundamental issues of nonequilibrium quantum statistical mechanics, the general framework presented in this work may be applied to a study of the dynamics of second order phase transitions in a wide variety of Landau-Ginsburg systems described by a scalar order parameter.