Measuring R-parity-violating couplings in dilepton production at the LHC

We revisit the issue of probing R-violating couplings of supersymmetric theories at hadronic colliders, particularly at the LHC. Concentrating on dimuon production, an evaluation of the optimal sensitivity to the R-violating coupling is performed through a maximum likelihood analysis. The measurement uncertainties are evaluated through a study of fully generated events processed through a fast simulation of the ATLAS detector. It is found that a host of R-violating couplings can be measured to a statistical accuracy of better than 10%, over a significant part of the m_{tilde f} -- lambda parameter space still allowed by low energy measurements. Since the bounds thus obtained do not simply scale as the squark mass, one can do significantly better at the LHC than at the Tevatron. The same analysis can also be extended to assess the reach of the LHC to effects due to any non-SM structure of the four-fermion amplitude, caused by exchanges of new particles with different spins such as leptoquarks and gravitons that are suggested by various theoretical ideas.Comment: 28 pages, 14 figures (uses JHEP3.cls

Implications of LHC Searches on SUSY Particle Spectra: The pMSSM Parameter Space with Neutralino Dark Matter

We study the implications of LHC searches on SUSY particle spectra using flat scans of the 19-parameter pMSSM phase space. We apply constraints from flavour physics, g_mu-2, dark matter and earlier LEP and Tevatron searches. The sensitivity of the LHC SUSY searches with jets, leptons and missing energy is assessed by reproducing with fast simulation the recent CMS analyses after validation on benchmark points. We present results in terms of the fraction of pMSSM points compatible with all the constraints which are excluded by the LHC searches with 1 fb^{-1} and 15 fb^{-1} as a function of the mass of strongly and weakly interacting SUSY particles. We also discuss the suppression of Higgs production cross sections for the MSSM points not excluded and contrast the region of parameter space tested by the LHC data with the constraints from dark matter direct detection experiments.Comment: 14 pages, 13 figures. v2: increased statistics, to appear in EPJ

A study of single sneutrino production in association with fermion pairs at polarised photon colliders

We investigate single sneutrino production in the context of R-parity-violating Supersymmetry at future $\gamma\gamma$ linear colliders. The sneutrino is produced in association with fermion pairs and it is shown that its decays into two further fermions will lead to a clean signal. We also discuss possible backgrounds and the effects of beam polarisation.Comment: 31 pages, LaTeX, 10 postscript figures. Title has been modified. Two new figures and one appendix added. Detailed SM background estimations were made. A new reference added. Version to appear in PR

A Note on Inflation with Tachyon Rolling on the Gauss-Bonnet Brane

In this paper we study the tachyonic inflation in brane world cosmology with Gauss-Bonnet term in the bulk. We obtain the exact solution of slow roll equations in case of exponential potential. We attempt to implement the proposal of Lidsey and Nunes, astro-ph/0303168, for the tachyon condensate rolling on the Gauss-Bonnet brane and discuss the difficulties associated with the proposal.Comment: RevTex4, 5 pages, no figures, Minor clarifications added and references updated, To appear in PR

Dynamics of Tachyon and Phantom Field beyond the Inverse Square Potentials

We investigate the cosmological evolution of the tachyon and phantom-tachyon scalar field by considering the potential parameter $\Gamma$($=\frac{V V"}{V'^2}$) as a function of another potential parameter $\lambda$($=\frac{V'}{\kappa V^{3/2}}$), which correspondingly extends the analysis of the evolution of our universe from two-dimensional autonomous dynamical system to the three-dimension. It allows us to investigate the more general situation where the potential is not restricted to inverse square potential and .One result is that, apart from the inverse square potential, there are a large number of potentials which can give the scaling and dominant solution when the function $\Gamma(\lambda)$ equals $3/2$ for one or some values of $\lambda_{*}$ as well as the parameter $\lambda_{*}$ satisfies condition Eq.(18) or Eq.(19). We also find that for a class of different potentials the dynamics evolution of the universe are actually the same and therefore undistinguishable.Comment: 8 pages, no figure, accepted by The European Physical Journal C(2010), online first, http://www.springerlink.com/content/323417h708gun5g8/?p=dd373adf23b84743b523a3fa249d51c7&pi=

Tachyonic Inflation in a Warped String Background

We analyze observational constraints on the parameter space of tachyonic inflation with a Gaussian potential and discuss some predictions of this scenario. As was shown by Kofman and Linde, it is extremely problematic to achieve the required range of parameters in conventional string compactifications. We investigate if the situation can be improved in more general compactifications with a warped metric and varying dilaton. The simplest examples are the warped throat geometries that arise in the vicinity of of a large number of space-filling D-branes. We find that the parameter range for inflation can be accommodated in the background of D6-branes wrapping a three-cycle in type IIA. We comment on the requirements that have to be met in order to realize this scenario in an explicit string compactification.Comment: Latex, JHEP class, 20 pages, 4 figures. v2: references added, small error in section 7 corrected, published versio

Non-minimally Coupled Tachyonic Inflation in Warped String Background

We show that the non-minimal coupling of tachyon field to the scalar curvature, as proposed by Piao et al, with the chosen coupling parameter does not produce the effective potential where the tachyon field can roll down from T=0 to large $T$ along the slope of the potential. We find a correct choice of the parameters which ensures this requirement and support slow-roll inflation. However, we find that the cosmological parameter found from the analysis of the theory are not in the range obtained from observations. We then invoke warped compactification and varying dilaton field over the compact manifold, as proposed by Raeymaekers, to show that in such a setup the observed parameter space can be ensured.Comment: minor typos corrected and references adde

The processes e−e+→γγ,Zγ,ZZe^-e^+\to\gamma\gamma, Z \gamma, ZZ in SM and MSSM

We present the results of a complete analysis of the one loop electroweak corrections to $e^-e^+\to\gamma\gamma, ~Z\gamma, ~ZZ$ in the Standard (SM) and the Minimal Supersymmetric Standard Model (MSSM). A special emphasis is put on the high energy behaviour of the various helicity amplitudes and the way the logarithmic structure is generated. The large magnitude of these effects, which induce striking differences between the SM and MSSM cases at high energies, offers the possibility of making global tests which could check the consistency of these models, and even decide whether any additional new physics is required.Comment: Short version (16 pages and 9 figures) of the paper hep-ph/0207273, to appear in Phy.Rev.D. e-mail: [email protected]

B_s --> mu+ mu- decay in the R-parity violating minimal supergravity

We study B_s --> mu+ mu- in the context of the R-parity violating minimal supergravity in the high tan beta regime. We find that the lowest value of the branching ratio can go well below the present LHCb sensitivity and hence B_s --> mu+ mu- can even be invisible to the LHC. We also find that the present upper bound on Br(B_s --> mu+ mu-) puts strong constraint on the minimal supergravity parameter space. The constraints become more severe if the upper bound is close to its standard model prediction.Comment: 18 pages, 10 figures; version to be published in European Physical Journal

Probing bilinear R-parity violating supergravity at the LHC

We study the collider phenomenology of bilinear R-parity violating supergravity, the simplest effective model for supersymmetric neutrino masses accounting for the current neutrino oscillation data. At the CERN Large Hadron Collider the center-of-mass energy will be high enough to probe directly these models through the search for the superpartners of the Standard Model (SM) particles. We analyze the impact of R-parity violation on the canonical supersymmetry searches - that is, we examine how the decay of the lightest supersymmetric particle (LSP) via bilinear R-parity violating interactions degrades the average expected missing momentum of the reactions and show how this diminishes the reach in the 'usual' channels for supersymmetry searches. However, the R-parity violating interactions lead to an enhancement of the final states containing isolated same-sign di-leptons and trileptons, compensating the reach loss in the fully inclusive channel. We show how the searches for displaced vertices associated to LSP decay substantially increase the coverage in supergravity parameter space, giving the corresponding reaches for two reference luminosities of 10 and 100 fb$^{-1}$ and compare with those of the R-parity conserving minimal supergravity model.Comment: Corrected version. To appear at JHE