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.
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.
15712084
Two-loop divergences of massive scattering amplitudes in non-abelian gauge theories
The infrared divergences of QCD scattering amplitudes can be derived from an anomalous dimension Γ, which is a matrix in color space and depends on the momenta and masses of the external partons. It has recently been shown that in cases where there are at least two massive partons involved in the scattering process, starting at two-loop order Γ receives contributions involving color and momentum correlations between three (and more) partons. The three-parton correlations can be described by two universal functions F1 and f2. In this paper these functions are calculated at two-loop order in closed analytic form and their properties are studied in detail. Both functions are found to be suppressed like (m4/s2) in the limit of small parton masses, in accordance with mass factorization theorems proposed in the literature. On the other hand, both functions are (1) and even diverge logarithmically near the threshold for pair production of two heavy particles. As an application, we calculate the infrared poles in the q → t and gg → t scattering amplitudes at two-loop order.
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.
124791746
Soft gluon resummation in t anti-t production at hadron colliders
We discuss results for the total and differential cross sect ions in top-quark pair production at hadron colliders. The focus is on a comparison of the next-to-leading order results with those based on soft gluon resummation to next-to-next-to-leading logarithmic accuracy.
119308511
Top quark pair production at small transverse momentum in hadronic collisions
We investigate the transverse momentum resummation for top quark pair production at hadron colliders using the soft-collinear effective theory and the heavy-quark effective theory. We derive the factorization formula for $t\bar{t}$ production at small pair transverse momentum, and show in detail the procedure for calculating the key ingredient of the factorization formula: the next-to-leading order soft functions. We compare our numerical results with experimental data and find that they are consistent within theoretical and experimental uncertainties. To verify the correctness of our resummation formula, we expand it to the next-to-leading order and the next-to-next-to-leading order, and compare those expressions with the exact fixed-order results numerically. Finally, using the results of transverse momentum resummation, we discuss the transverse-momentum-dependent forward-backward asymmetry at the Tevatron.