The constrained E6SSM

We discuss the predictions of a constrained version of the exceptional supersymmetric standard model (cE6SSM), with a universal high energy soft scalar mass, soft trilinear coupling and soft gaugino mass. The spectrum includes a light gluino, a light wino-like neutralino and chargino pair and a light bino-like neutralino, with other sparticle masses except the lighter stop being much heavier. We also discuss scenarios with an extra light exotic colour triplet of fermions and scalars and a TeV scale Z', which lead to early exotic physics signals at the LHC.Comment: To appear in proceedings of The 2009 Europhysics Conference on High Energy Physics, 16-22 July 2009 Krakow, Poland; 4 page

Collapses and revivals of stored orbital angular momentum of light in a cold atomic ensemble

We report on the storage of orbital angular momentum of light in a cold ensemble of cesium atoms. We employ Bragg diffraction to retrieve the stored optical information impressed into the atomic coherence by the incident light fields. The stored information can be manipulated by an applied magnetic field and we were able to observe collapses and revivals due to the rotation of the stored atomic Zeeman coherence for times longer than 15 $\mu s$.Comment: Submitted to Physical Review

Intrinsic scatter of caustic masses and hydrostatic bias: An observational study

All estimates of cluster mass have some intrinsic scatter and perhaps some bias with true mass even in the absence of measurement errors for example caused by cluster triaxiality and large scale structure. Knowledge of the bias and scatter values is fundamental for both cluster cosmology and astrophysics. In this paper we show that the intrinsic scatter of a mass proxy can be constrained by measurements of the gas fraction because masses with higher values of intrinsic scatter with true mass produce more scattered gas fractions. Moreover, the relative bias of two mass estimates can be constrained by comparing the mean gas fraction at the same (nominal) cluster mass. Our observational study addresses the scatter between caustic (i.e., dynamically estimated) and true masses, and the relative bias of caustic and hydrostatic masses. For these purposes, we used the X-ray Unbiased Cluster Sample, a cluster sample selected independently from the intracluster medium content with reliable masses: 34 galaxy clusters in the nearby ($0.050<z<0.135$) Universe, mostly with $14<\log M_{500}/M_\odot \lesssim 14.5$, and with caustic masses. We found a 35\% scatter between caustic and true masses. Furthermore, we found that the relative bias between caustic and hydrostatic masses is small, $0.06\pm0.05$ dex, improving upon past measurements. The small scatter found confirms our previous measurements of a highly variable amount of feedback from cluster to cluster, which is the cause of the observed large variety of core-excised X-ray luminosities and gas masses.Comment: A&A, in press, minor language changes from previous versio

NMSSM Higgs Discovery at the LHC

We demonstrate that Higgs discovery at the LHC is possible in the context of the NMSSM even for those scenarios such that the only strongly produced Higgs boson is a very SM-like CP-even scalar which decays almost entirely to a pair of relatvely light CP-odd states. In combination with other search channels, we are on the verge of demonstrating that detection of at least one of the NMSSM Higgs bosons is guaranteed at the LHC for accumulated luminosity of $300 {\rm fb}^{-1}$.Comment: 8 pages, 1 figure, to appear in the Proceedings of the Les Houches Workshop 2003: ``Physics at TeV Colliders'

Determining the ratio of the H^+ -> \tau \nu to H^+ -> t b-bar decay rates for large \tan\beta at the Large Hadron Collider

We present results on the determination of the observable ratio R=BR(H^+ -> \tau \nu)/BR(H^+ -> t b-bar) of charged Higgs boson decay rates as a discriminant quantity between Supersymmetric and non-Supersymmetric models. Simulation of measurements of this quantity through the analysis of the charged Higgs production process gb-> t b H^+ and relative backgrounds in the two above decay channels has been performed in the context of ATLAS. A ~12-14% accuracy on R can be achieved for \tan\beta=50, \mHc=300-500 GeV and after an integrated luminosity of 300 fb^-1. With this precision measurement, the Large Hadron Collider (LHC) can easily discriminate between models for the two above scenarios, so long as \tan\beta > 20.Comment: LaTeX, 11 pages, 3 figures, 3 tables, Contribution to the Les Houches workshop ``Physics at TeV Colliders'', 26 May - 6 June, 200

Credibility and Policy Convergence: Evidence from U.S. House Roll Call Voting Records

Traditional models of politician behavior predict complete or partial policy convergence, whereby electoral competition compels partisan politicians to choose positions more moderate than their most-preferred policies. Alternatively, if politicians cannot overcome the inability to make binding pre-commitments to policies, the expected result is complete policy divergence. By exploiting a regression discontinuity (RD) design inherent in the Congressional electoral system, this paper empirically tests the strong predictions of the complete divergence hypothesis against the alternative of partial convergence within the context of Representatives' roll call voting behavior in the U.S. House (1946-1994). The RD design implies that which party wins a district seat is quasi-randomly assigned among elections that turn out to be 'close'. We use this variation to examine if Representatives' roll call voting patterns do not respond to large exogenous changes in the probability of winning the election, the strong prediction of complete policy divergence. The evidence is more consistent with full divergence and less consistent with partial convergence, suggestive that the difficulty of establishing credible commitments to policies is an important real-world phenomenon.