Search for new physics with ATLAS at the LHC

Due to the high energy and luminosity of the LHC, the ATLAS experiment has a huge discovery potential for new physics. A Standard Model Higgs boson can be discovered over the full range of allowed masses, and its mass should be measured with a precision of about 0.1%. The Higgs sector of the MSSM should be fully explored by searches for supersymmetric Higgs bosons. Squarks and gluinos can be discovered up to masses of 2.5 TeV and several precision measurements can be performed in the SUSY sector. The existence of particles predicted by other theories beyond the Standard Model has been also investigated.Comment: 6 pages LaTeX, 4 eps figures and 1 style file incorporated. Presented at the Lake Louise Winter Institute 2000: From Particles to the Universe, Alberta, Canada, 20-26 February 200

METing SUSY on the Z peak

Recently the ATLAS experiment announced a 3 $\sigma$ excess at the Z-peak consisting of 29 pairs of leptons together with two or more jets, $E_T^{\rm miss}> 225$ GeV and $H_T \geq 600$ GeV, to be compared with $10.6 \pm 3.2$ expected lepton pairs in the Standard Model. No excess outside the Z-peak was observed. By trying to explain this signal with SUSY we find that only relatively light gluinos, $m_{\tilde g} \lesssim 1.2$ TeV, together with a heavy neutralino NLSP of $m_{\tilde \chi} \gtrsim 400$ GeV decaying predominantly to Z-boson plus a light gravitino, such that nearly every gluino produces at least one Z-boson in its decay chain, could reproduce the excess. We construct an explicit general gauge mediation model able to reproduce the observed signal overcoming all the experimental limits. Needless to say, more sophisticated models could also reproduce the signal, however, any model would have to exhibit the following features, light gluinos, or heavy particles with a strong production cross-section, producing at least one Z-boson in its decay chain. The implications of our findings for the Run II at LHC with the scaling on the Z peak, as well as for the direct search of gluinos and other SUSY particles, are pointed out.Comment: 24 pages, 17 figures, simulation improved, Checkmate analysis added, new benchmark point included. Typos corrected, conclusions unchange

Histogram comparison as a powerful tool for the search of new physics at LHC. Application to CMSSM

We propose a rigorous and effective way to compare experimental and theoretical histograms, incorporating the different sources of statistical and systematic uncertainties. This is a useful tool to extract as much information as possible from the comparison between experimental data with theoretical simulations, optimizing the chances of identifying New Physics at the LHC. We illustrate this by showing how a search in the CMSSM parameter space, using Bayesian techniques, can effectively find the correct values of the CMSSM parameters by comparing histograms of events with multijets + missing transverse momentum displayed in the effective-mass variable. The procedure is in fact very efficient to identify the true supersymmetric model, in the case supersymmetry is really there and accessible to the LHC

Constraining Scalar Leptoquarks from the K and B Sectors

Upper bounds at the weak scale are obtained for all $\lambda_{ij}\lambda_{im}$ type product couplings of the scalar leptoquark model which may affect K-K(bar), B_d-B_d(bar), and B_s-B_s(bar)$ mixing, as well as leptonic and semileptonic K and B decays. Constraints are obtained for both real and imaginary parts of the couplings. We also discuss the role of leptoquarks in explaining the anomalously large CP-violating phase in B_s-B_s(bar) mixing.Comment: 16 pages, 5 figures, more constraints analyzed, added a number of reference

Prospects for discovering supersymmetric long-lived particles with MoEDAL

We present a study on the possibility of searching for long-lived supersymmetric partners with the MoEDAL experiment at the LHC. MoEDAL is sensitive to highly ionising objects such as magnetic monopoles or massive (meta)stable electrically charged particles. We focus on prospects of directly detecting long-lived sleptons in a phenomenologically realistic model which involves an intermediate neutral long-lived particle in the decay chain. This scenario is not yet excluded by the current data from ATLAS or CMS, and is compatible with astrophysical constraints. Using Monte Carlo simulation, we compare the sensitivities of MoEDAL versus ATLAS in scenarios where MoEDAL could provide discovery reach complementary to ATLAS and CMS, thanks to looser selection criteria combined with the virtual absence of background. It is also interesting to point out that, in such scenarios, in which charged staus are the main long-lived candidates, the relevant mass range for MoEDAL is compatible with a potential role of Supersymmetry in providing an explanation for the anomalous events observed by the ANITA detector.Comment: 12 pages, 6 figures; preliminary results presented in arXiv:1903.11022; matches published version in EPJ

Constraining super-critical string/brane cosmologies with astrophysical data

We discuss fits of unconventional dark energy models to the available data from high-redshift supernovae, distant galaxies and baryon oscillations. The models are based either on brane cosmologies or on Liouville strings in which a relaxation dark energy is provided by a rolling dilaton field (Q-cosmology). Such cosmologies feature the possibility of effective four-dimensional negative-energy dust and/or exotic scaling of dark matter. We find evidence for a negative-energy dust at the current era, as well as for exotic-scaling (a^{-delta}) contributions to the energy density, with delta ~= 4, which could be due to dark matter coupling with the dilaton in Q-cosmology models. We conclude that Q-cosmology fits the data equally well with the LambdaCDM model for a range of parameters that are in general expected from theoretical considerations.Comment: 4 pages, 2 figures, Contributed to 11th International Conference on Topics in Astroparticle and Underground Physics (TAUP 2009) 1-5 Jul 2009, Rome, Italy; J. Phys. Conf. Series to appea

Dark matter searches at LHC

Besides Standard Model measurements and other Beyond Standard Model studies, the ATLAS and CMS experiments at the LHC will search for Supersymmetry, one of the most attractive explanation for dark matter. The SUSY discovery potential with early data is presented here together with some first results obtained with 2010 collision data at 7 TeV. Emphasis is placed on measurements and parameter determination that can be performed to disentangle the possible SUSY models and SUSY look-alike and the interpretation of a possible positive supersymmetric signal as an explanation of dark matter.Comment: 15 pages, 14 figures, Invited plenary talk given at DISCRETE 2010: Symposium On Prospects In The Physics Of Discrete Symmetries, 6-11 Dec 2010, Rome, Ital

Astrophysical Probes of the Constancy of the Velocity of Light

We discuss possible tests of the constancy of the velocity of light using distant astrophysical sources such as gamma-ray bursters (GRBs), Active Galactic Nuclei (AGNs) and pulsars. This speculative quest may be motivated by some models of quantum fluctuations in the space-time background, and we discuss explicitly how an energy-dependent variation in photon velocity \delta c/ c \sim - E / M arises in one particular quantum-gravitational model. We then discuss how data on GRBs may be used to set limits on variations in the velocity of light, which we illustrate using BATSE and OSSE observations of the GRBs that have recently been identified optically and for which precise redshifts are available. We show how a regression analysis can be performed to look for an energy-dependent effect that should correlate with redshift. The present data yield a limit M \gsim 10^{15} GeV for the quantum gravity scale. We discuss the prospects for improving this analysis using future data, and how one might hope to distinguish any positive signal from astrophysical effects associated with the sources.Comment: 37 pages LaTeX, 9 eps figures included, uses aasms4.st