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.
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.
119074816
Supersymmetric QCD corrections to single top quark production at hadron colliders
We present the calculations of the supersymmetric QCD corrections to the total cross sections for single top production at the Fermilab Tevatron and the CERN Large Hadron Collider in the minimal supersymmetric standard model. Our results show that, for the s-channel and t-channel, the supersymmetric QCD corrections are at most about 1%, but for the associated production process pp{yields}tW, the supersymmetric QCD corrections increase the total cross sections significantly, which can reach about 6% for most values of the parameters. Thus, the supersymmetric QCD corrections should be taken into consideration in future high precision experimental analyses for top physics.
118485597
Renormalization-group improved predictions for top-quark pair production at hadron colliders
Precision predictions for phenomenologically interesting observables such as the $ t\bar{t} $ invariant mass distribution and forward-backward asymmetry in top-quark pair production at hadron colliders require control over the differential cross section in perturbative QCD. In this paper we improve existing calculations of the doubly differential cross section in the invariant mass and scattering angle by using techniques from soft-collinear effective theory to perform an NNLL resummation of threshold logarithms, which become large when the invariant mass M of the top-quark pair approaches the partonic center-of-mass energy $ \sqrt {{\hat{s}}} $. We also derive an approximate formula for the differential cross section at NNLO in fixed-order perturbation theory, which completely determines the coefficients multiplying the singular plus distributions in the variable $ \left( {1 - {{{{M^2}}} \left/ {{\hat{s}}} \right.}} \right) $. We then match our results in the threshold region with the exact results at NLO in fixed-order perturbation theory, and perform a numerical analysis of the invariant mass distribution, the total cross section, and the forward-backward asymmetry. We argue that these are the most accurate predictions available for these observables at present. Using MSTW2008NNLO parton distribution functions (PDFs) along with αs(MZ) = 0.117 and mt = 173.1 GeV, we obtain for the inclusive production cross sections at the Tevatron and LHC the values $ {{{\sigma }}_{\text{Tevatron}}} = \left( {6.30\pm 0.19_{ - 0.23}^{ + 0.31}} \right){\text{pb}} $ and σLHC = (149 ± 7 ± 8) pb, where the first error results from scale variations while the second reflects PDF uncertainties.
118683262
The NNLO soft function for the pair invariant mass distribution of boosted top quarks
A bstractAt high values of the pair invariant mass the differential cross section for top-quark pair production at hadron colliders factorizes into soft, hard, and fragmentation functions. In this paper we calculate the next-to-next-to-leading-order (NNLO) corrections to the soft function appearing in this factorization formula, thus providing the final piece needed to evaluate at NNLO the differential cross section in the virtual plus soft approximation in the large invariant-mass limit. Technically, this amounts to evaluating the vacuum expectation value of a soft Wilson loop operator built out of light-like Wilson lines for each of the four partons participating in the hard scattering process, with a certain constraint on the total energy of the soft radiation. Our result turns out to be surprisingly simple, because in the sum of all graphs the three and four parton contributions multiply color structures whose coefficients are governed by the non-abelian exponentiation theorem.