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.
41932928
Calculation of the transverse parton distribution functions at next-to-next-to-leading order
A bstractWe describe the perturbative calculation of the transverse parton distribution functions in all partonic channels up to next-to-next-to-leading order based on a gauge invariant operator definition. We demonstrate the cancellation of light-cone divergences and show that universal process-independent transverse parton distribution functions can be obtained through a refactorization. Our results serve as the first explicit higher-order calculation of these functions starting from first principles, and can be used to perform next-to-next-to-next-to-leading logarithmic qT resummation for a large class of processes at hadron colliders.
52970299
NNLL momentum-space threshold resummation in direct top quark production at the LHC
A bstractWe update the theoretical precision of the total cross section for direct top quark production at the LHC by extending the threshold resummation to the next-to-next-to-leading logarithmic accuracy.
121334149
TOP-CHARM ASSOCIATED PRODUCTION VIA SUSY FCNC COUPLINGS AT THE CERN LHC IN THE MSSM
We evaluate the total cross-sections of top-charm associated production induced by SUSY–QCD FCNC at the LHC within the general unconstrained MSSM framework. Our results show that these production rates may be as large as a few pb for favorable parameter values allowing by current precise experiments. It means that the LHC may produce abundant events of this process, and the SUSY FCNC effects through the above process may be observable in the future experiments.
118885118
Origin of the Large Perturbative Corrections to Higgs Production at Hadron Colliders
The very large K factor for Higgs-boson production at hadron colliders is shown to result from enhanced perturbative corrections of the form (C{sub A}{pi}{alpha}{sub s}){sup n}, which arise in the analytic continuation of the gluon form factor to timelike momentum transfer. These terms are resummed to all orders in perturbation theory using the renormalization group. After the resummation, the K factor for the production of a light Higgs boson at the LHC is reduced to a value close to 1.3.
56269051
Updated Predictions for Higgs Production at the Tevatron and the LHC
Abstract We present updated predictions for the total cross section for Higgs boson production through gluon fusion at hadron colliders. In addition to renormalization-group improvement at next-to-next-to-next-to-leading logarithmic accuracy, we incorporate the two-loop electroweak corrections, which leads to the most precise predictions at present. Numerical results are given for Higgs masses between 115 GeV and 200 GeV at the Tevatron with s = 1.96 TeV and the LHC with s = 7 – 14 TeV .
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.
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.
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.