Infrared Singularities and Soft Gluon Resummation with Massive Partons
Infrared divergences of QCD scattering amplitudes can be derived from an anomalous dimension matrix, which is also an essential ingredient for the resummation of large logarithms due to soft gluon emissions. We report a recent analytical calculation of the anomalous dimension matrix with both massless and massive partons at two-loop level, which describes the two-loop infrared singularities of any scattering amplitudes with an arbitrary number of massless and massive partons, and also enables soft gluon resummation at next-to-next-to-leading-logarithmic order. As an application, we calculate the infrared poles in the q q ¯ → t t ¯ and g g → t t ¯ scattering amplitudes at two-loop order.

title: RG-improved single-particle inclusive cross sections and forward-backward asymmetry in $ t\bar{t} $ production at hadron colliders
abstract: We use techniques from soft-collinear effective theory (SCET) to derive renormalization-group improved predictions for single-particle inclusive (1PI) observables in top-quark pair production at hadron colliders. In particular, we study the top-quark transverse-momentum and rapidity distributions, the forward-backward asymmetry at the Tevatron, and the total cross section at NLO + NNLL order in resummed perturbation theory and at approximate NNLO in fixed order. We also perform a detailed analysis of power corrections to the leading terms in the threshold expansion of the partonic hard-scattering kernels. We conclude that, although the threshold expansion in 1PI kinematics is susceptible to numerically significant power corrections, its predictions for the total cross section are in good agreement with those obtained by integrating the top-pair invariant-mass distribution in pair invariant-mass kinematics, as long as a certain set of subleading terms appearing naturally within the SCET formalism is included.

title: Higgs boson self-coupling measurements using ratios of cross sections
abstract: A bstractWe consider the ratio of cross sections of double-to-single Higgs boson production at the Large Hadron Collider at 14 TeV. Since both processes possess similar higherorder corrections, leading to a cancellation of uncertainties in the ratio, this observable is well-suited to constrain the trilinear Higgs boson self-coupling. We consider the scale variation, parton density function uncertainties and conservative estimates of experimental uncertainties, applied to the viable decay channels, to construct expected exclusion regions. We show that the trilinear self-coupling can be constrained to be positive with a 600 fb−1 LHC dataset at 95% confidence level. Moreover, we demonstrate that we expect to obtain a ~ +30% and ~ −20% uncertainty on the self-coupling at 3000fb−1 without statistical fitting of differential distributions. The present article outlines the most precise method of determination of the Higgs trilinear coupling to date.

title: Soft-gluon resummation for boosted top-quark production at hadron colliders
abstract: 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.

title: Higgs boson pair production at the LHC in the $b \bar{b} W^+ W^-$ channel
abstract: 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 $\lambda$.

title: Soft gluon resummation effects in single slepton production at hadron colliders
abstract: 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.

title: Warmth Elevating the Depths: Shallower Voids with Warm Dark Matter
abstract: Author(s): Yang, LF; Neyrinck, MC; Aragon-Calvo, MA; Falck, B; Silk,  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.

title: Dark matter contribution to Galactic diffuse gamma ray emission
abstract: Author(s): Yang, Lin F; Silk, Joseph; Szalay, Alexander S; Wyse, Rosemary FG; Bozek, Brandon; Madau,  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.

title: Ringing the initial Universe: the response of overdensity and transformed-density power spectra to initial spikes
abstract: 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.