7421495
Soft gluon resummation effects in single slepton production at hadron colliders
We investigate QCD effects in the production of a single slepton at hadron colliders in the minimal supersymmetric standard model without R parity. We calculate the total cross sections and the transverse momentum distributions at next-to-leading order in QCD. The next-to-leading-order corrections enhance the total cross sections and decrease the dependence of the total cross sections on the factorization and renormalization scales. For the differential cross sections, we resum all-order soft gluon effects to give reliable predictions for the transverse momentum distributions. We also compare two approaches to the nonperturbative parametrization and found that the results are slightly different at the Tevatron and are in good agreement at the Large Hadron Collider. Our results can be useful to the simulation of the events and to the future collider experiments.
118312859
The top-pair forward-backward asymmetry beyond NLO
Institute for Theoretical Physics, University of Zu¨rich, CH-8057 Zu¨rich, Switzerland(Dated: July 1, 2011)We make use of recent results in eﬀective theory and higher-order perturbative calculations to im-prove the theoretical predictions of the QCD contribution to the top-quark pair production forward-backward asymmetry at the Tevatron. In particular, we supplement the ﬁxed-order NLO calculationwith higher-order corrections from soft gluon resummation at NNLL accuracy performed in two dif-ferent kinematic schemes, which allows us to make improved predictions for the asymmetry in thepp¯ and t¯trest frames as a function of the rapidity and invariant mass of the t¯tpair. Furthermore,we provide binned results which can be compared with the recent measurements of the forward-backward asymmetry in events with a large pair invariant mass or rapidity diﬀerence. Finally, wecalculate at NLO+NNLL order the top-quark charge asymmetry at the LHC as a function of a lowerrapidity cut-oﬀ for the top and antitop quarks.I. INTRODUCTION
31324713
Soft gluon resummation effects in single graviton production at the CERN Large Hadron Collider in the Randall-Sundrum model
We study QCD effects in single graviton production at the CERN Large Hadron Collider (LHC) in the Randall-Sundrum (RS) model. We present in detail the complete next-to-leading order (NLO) QCD corrections to the inclusive total cross sections. The NLO QCD corrections enhance significantly the total cross sections and decrease efficiently the dependence of the total cross sections on the factorization and renormalization scales. We also examine the uncertainty of the total cross sections due to the parton distribution function (PDF) uncertainties. For the differential cross sections on the transverse momentum (q{sub T}) of the graviton, within the CSS resummation formalism, we resum the logarithmically-enhanced terms at small q{sub T} to all orders up to NLO logatithmic accuracy. Combined with the fixed-order calculations, we give consistent predictions for both small q{sub T} and large q{sub T}.
118714824
Soft-gluon resummation for boosted top-quark production at hadron colliders
We investigate the production of highly energetic top-quark pairs at hadron colliders, focusing on the case where the invariant mass of the pair is much larger than the mass of the top quark. In particular, we set up a factorization formalism appropriate for describing the differential partonic cross section in the double soft and small-mass limit, and explain how to resum simultaneously logarithmic corrections arising from soft gluon emission and from the ratio of the pair-invariant mass to that of the top quark to next-to-next-to-leading logarithmic accuracy. We explore the implications of our results on approximate next-to-next-to-leading order formulas for the differential cross section in the soft limit, pointing out that they offer a simplified calculational procedure for determining the currently unknown delta-function terms in the limit of high invariant mass.
10304009
Higgs boson pair production at the LHC in the $b \bar{b} W^+ W^-$ channel
We consider Higgs boson pair production at the LHC in the $b \bar{b} W^+ W^-$ channel, with subsequent decay of the $W^+W^-$ pair into $\ell \nu j j$. Employing jet substructure and event reconstruction techniques, we show that strong evidence for this channel can be found at the 14 TeV LHC with 600 fb$^{-1}$ of integrated luminosity, thus improving the current reach for the production of Higgs boson pairs. This measurement will allow to probe the trilinear Higgs boson coupling $\lambda$.
32442094
Threshold resummation effects in direct top quark production at hadron colliders
We investigate the threshold-enhanced QCD corrections to the cross sections for direct top quark productions induced by model-independent flavor changing neutral current couplings at hadron colliders. We use the soft-collinear effective theory to describe the incoming massless partons and use the heavy quark effective theory to treat the top quark. Then we construct the flavor changing operator based on the above effective theories, and resum the large logarithms near threshold arising from soft gluon emission. Our results show that the resummed QCD corrections further enhance the next-to-leading order cross sections significantly. Moreover, the resummation effects vastly reduce the dependence of the cross sections on the renormalization and factorization scales, especially in cases where the next-to-leading order results behave worse than the leading order results. Our results are more sensitive to the new physics effects. If signals of direct top quark production are found in future experiments, it is more appropriate to use our results as the theoretical inputs for extracting the anomalous couplings.
118495969
Dark matter contribution to Galactic diffuse gamma ray emission
Author(s): Yang, Lin F; Silk, Joseph; Szalay, Alexander S; Wyse, Rosemary FG; Bozek, Brandon; Madau, Piero | Abstract: Observations of diffuse Galactic gamma ray emission (DGE) by the Fermi Large Area Telescope (LAT) allow a detailed study of cosmic rays and the interstellar medium. However, diffuse emission models of the inner Galaxy underpredict the Fermi-LAT data at energies above a few GeV and hint at possible nonastrophysical sources including dark matter (DM) annihilations or decays. We present a study of the possible emission components from DM using the high-resolution Via Lactea II N-body simulation of a Milky Way - sized DM halo. We generate full-sky maps of DM annihilation and decay signals that include modeling of the adiabatic contraction of the host density profile, Sommerfeld-enhanced DM annihilations, p-wave annihilations, and decaying DM. We compare our results with the DGE models produced by the Fermi-LAT team over different sky regions, including the Galactic center, high Galactic latitudes, and the Galactic anticenter. This work provides possible smooth component templates of DM to fit the observational data. The subhalo contributions can be considered to provide statistically meaningful templates and demonstrate how spatial profiles are significantly modified according to different annihilation or decay scenarios. We argue that a subhalo-based approach can help constrain the DM physics. © 2014 American Physical Society.
73704985
Warmth Elevating the Depths: Shallower Voids with Warm Dark Matter
Author(s): Yang, LF; Neyrinck, MC; Aragon-Calvo, MA; Falck, B; Silk, J | Abstract: © 2015 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. Warm dark matter (WDM) has been proposed as an alternative to cold dark matter (CDM), to resolve issues such as the apparent lack of satellites around the MilkyWay. Even ifWDMis not the answer to observational issues, it is essential to constrain the nature of the dark matter. The effect of WDM on haloes has been extensively studied, but the small-scale initial smoothing in WDM also affects the present-day cosmic web and voids. It suppresses the cosmic 'subweb' inside voids, and the formation of both void haloes and subvoids. In N-body simulations run with different assumed WDM masses, we identify voids with the ZOBOV algorithm, and cosmic-web components with the ORIGAMI algorithm. As dark-matter warmth increases (i.e. particle mass decreases), void density minima grow shallower, while void edges change little. Also, the number of subvoids decreases. The density field in voids is particularly insensitive to baryonic physics, so if void density profiles and minima could be measured observationally, they would offer a valuable probe of the nature of dark matter. Furthermore, filaments and walls become cleaner, as the substructures in between have been smoothed out; this leads to a clear, mid-range peak in the density PDF.
117767569
Study of a magnetic alloy-loaded RF cavity for bunch compression at the CSR
The Heavy Ion Research Facility and Cooling Storage Ring (HIRFL-CSR) accelerator in Lanzhou offers a unique possibility for the generation of high density and short pulse heavy ion beams by non-adiabatic bunch compression longitudinally, which is implemented by a fast jump of the RF-voltage amplitude. For this purpose, an RF cavity with high electric field gradient loaded with Magnetic Alloy cores has been developed. The results show that the resonant frequency range of the single-gap RF cavity is from 1.13 MHz to 1.42 MHz, and a maximum RF voltage of 40 kV with a total length of 100 cm can be obtained, which can be used to compress heavy ion beams of 238U72+ with 250 MeV/u from the initial bunch length of 200 ns to 50 ns with the coaction of the two single-gap RF cavity mentioned above.
118851111
Ringing the initial Universe: the response of overdensity and transformed-density power spectra to initial spikes
We present an experiment in which we 'ring' a set of cosmological N-body-simulation initial conditions, placing spikes in the initial power spectrum at different wavenumber bins. We then measure where these spikes end up in the final conditions. In the usual overdensity power spectrum, most sensitive to contracting and collapsing dense regions, initial power on slightly non-linear scales (k ~ 0.3 h/Mpc) smears to smaller scales, coming to dominate the initial power once there. Log-density and Gaussianized-density power spectra, sensitive to low-density (expanding) and high-density regions, respond differently: initial spikes spread symmetrically in scale, both upward and downward. In fact, in the power spectrum of 1/(1 + {\delta}), spikes migrate to larger scales, showing the magnifying effect of voids on small-scale modes. These power spectra show much greater sensitivity to small-scale initial features. We also test the difference between an approximation of the Ly-{\alpha} flux field, and its Gaussianized form, and give a toy model that qualitatively explains the symmetric power spreading in Gaussianized-density power spectra. Also, we discuss how to use this framework to estimate power-spectrum covariance matrices. This can be used to track the fate of information in the Universe, that takes the form of initial degrees of freedom, one random spike per initial mode.