15000252
Gauss-Bonnet braneworld cosmological effect on relic density of dark matter
In Gauss-Bonnet braneworld cosmology, the Friedmann equation of our four-dimensional Universe on 3-brane is modified in a high energy regime (Gauss-Bonnet regime), while the standard expansion law is reproduced in low energies (standard regime). We investigate the Gauss-Bonnet braneworld cosmological effect on the thermal relic density of cold dark matter when the freeze-out of the dark matter occurs in the Gauss-Bonnet regime. We find that the resultant relic density is considerably reduced when the transition temperature, which connects the Gauss-Bonnet regime with the standard regime, is low enough. This result is in sharp contrast with the result previously obtained in the Randall-Sundrum braneworld cosmology, where the relic density is enhanced.
117969552
Simple brane-world inflationary models in light of BICEP2
Motivated by the recent CMB $B$-mode observation announced by the BICEP2 collaboration, we study simple inflationary models in the Randall-Sundrum brane-world cosmology. Brane-world cosmological effects alter the inflationary predictions of the spectral index ($n_s$) and the tensor-to-scalar ratio ($r$) from those obtained in the standard cosmology. In particular, the tensor-to-scalar ratio is enhanced in the presence of the 5th dimension, and simple inflationary models which predict small $r$ values in the standard cosmology can yield $r$ values being compatible with the BICEP2 result, $r=0.2^{+0.07}_{-0.05}$. Confirmation of the BICEP2 result and more precise measurements of $n_s$ and $r$ in the near future allow us to constrain the 5-dimensional Planck mass ($M_5$) of the brane-world scenario. We also discuss the post inflationary scenario, namely, reheating of the universe through inflaton decay to the Standard Model particles. When we require the renormalizability of the inflationary models, the inflaton only couples with the Higgs doublet among the Standard Model fields, through which reheating process occurs. If $M_5$ is as low as $10^6$ GeV, the mass of inflaton becomes of ${\cal O}$(100 GeV), providing the inflationary predictions being consistent with the BICEP2 and Planck results. Such a light inflaton has some impacts on phenomenology at the electroweak scale through the coupling with the Higgs doublet.
117483857
Search for quark contact interactions in dijet angular distributions in pp collisions at s=7 TeV measured with the ATLAS detector
Dijet angular distributions from the first LHC pp collisions at center-of-mass energy sqrt(s) = 7 TeV have been measured with the ATLAS detector. The dataset used for this analysis represents an integrated luminosity of 3.1 pb-1. Dijet $\chi$ distributions and centrality ratios have been measured up to dijet masses of 2.8 TeV, and found to be in good agreement with Standard Model predictions. Analysis of the $\chi$ distributions excludes quark contact interactions with a compositeness scale $\Lambda$ below 3.4 TeV, at 95% confidence level, significantly exceeding previous limits.
113198029
Triggering on Long-Lived Neutral Particles in the ATLAS Detector
Neutral particles with long decay paths that decay to many-particle final states represent, from an experimental point of view, a challenge both for the trigger and for the reconstruction capabilities of the ATLAS apparatus. The Hidden Valley scenario serves as an excellent setting for the purpose of exploring the challenges to the trigger posed by long-lived particles.
122689361
Search for New Phenomena with the Monojet and Missing Transverse Momentum Signature Using the ATLAS Detector in $\sqrt{s}=7$ TeV Proton-Proton Collisions
A search for new phenomena in events featuring a high energy jet and large missing transverse momentum in proton-proton collisions at root s = 7 TeV is presented using a dataset corresponding to an integrated luminosity of 33 pb(-1) recorded with the ATLAS detector at the Large Hadron Collider. The number of observed events is consistent with the Standard Model prediction. This result is interpreted in terms of limits on a model of Large Extra Dimensions. (C) 2011 CERN. Published by Elsevier B.V. All rights reserved.
202105722
Search for strong gravity signatures in same-sign dimuon final states using the ATLAS detector at the LHC
A search for microscopic black holes has been performed in a same-sign dimuon final state using 1.3 fb(-1) of proton-proton collision data collected with the ATLAS detector at a centre of mass energy of 7 TeV at the CERN Large Hadron Collider. The data are found to be consistent with the expectation from the Standard Model and the results are used to derive exclusion contours in the context of a low scale gravity model.
197468931
Study of jet shapes in inclusive jet production in pp collisions at sqrt[s]=7 TeV using the ATLAS detector
Jet shapes have been measured in inclusive jet production in proton-proton collisions at sqrt(s) = 7 TeV using 3 pb^{-1} of data recorded by the ATLAS experiment at the LHC. Jets are reconstructed using the anti-kt algorithm with transverse momentum 30 GeV < pT < 600 GeV and rapidity in the region |y| < 2.8. The data are corrected for detector effects and compared to several leading-order QCD matrix elements plus parton shower Monte Carlo predictions, including different sets of parameters tuned to model fragmentation processes and underlying event contributions in the final state. The measured jets become narrower with increasing jet transverse momentum and the jet shapes present a moderate jet rapidity dependence. Within QCD, the data test a variety of perturbative and non-perturbative effects. In particular, the data show sensitivity to the details of the parton shower, fragmentation, and underlying event models in the Monte Carlo generators. For an appropriate choice of the parameters used in these models, the data are well described.