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}.
119293523
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.
51692158
Higgs boson pair production in the D = 6 extension of the SM
A bstractWe derive the constraints that can be imposed on the dimension-6 effective theory extension of the Standard Model, using gluon fusion-initiated Higgs boson pair production at the LHC. We use a realistic analysis focussing on the hh→bb¯τ+τ−$$ hh\to \left(b\overline{b}\right)\left({\tau}^{+}{\tau}^{-}\right) $$ final state, including initial-state radiation and non-perturbative effects. We include the statistical uncertainties on the signal rates as well as conservative estimates of the theoretical uncertainties. We first consider a theory containing only modifications of the trilinear coupling, through a c6λ H6/v2 Lagrangian term, and then examine the full parameter space of the effective theory, incorporating current bounds obtained through single Higgs boson measurements. We also consider an alternative scenario, where we vary a smaller sub-set of parameters. Allowing, finally, the values of the other coefficients to vary within projected experimental ranges, we find that the currently unbounded parameter, c6, could be constrained to lie within |c6| ≲ 0.6 at 1σ confidence, at the end of the high-luminosity run of the LHC (14 TeV) in the full model, and to −0.6 ≲ c6 ≲ 0.5 in the alternative model. This study constitutes a first step towards the inclusion of multi-Higgs boson production in a full fit to the dimension-6 effective field theory framework.
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.
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.
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.
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.