Bose-Einstein Final State Symmetrization for Event Generators of Heavy Ion Collisions

We discuss algorithms which allow to calculate identical two-particle correlations from numerical simulations of relativistic heavy ion collisions. A toy model is used to illustrate their properties.Comment: Talk given at CRIS'98 (Catania, June 8-12, 1998), to appear in "CRIS'98: Measuring the size of things in the Universe: HBT interferometry and heavy ion physics", (S. Costa et al., eds.), World Scientific, Singapore, 1998. (10 pages Latex, 1 eps-figure, extended version of conference proceedings, Fig1 a,b added and corresponding discussion enlarged

Bose-Einstein Correlations in a Space-Time Approach to e+ e- Annihilation into Hadrons

A new treatment of Bose-Einstein correlations is incorporated in a space-time parton-shower model for e+ e- annihilation into hadrons. Two alternative afterburners are discussed, and we use a simple calculable model to demonstrate that they reproduce successfully the size of the hadron emission region. One of the afterburners is used to calculate two-pion correlations in e+ e- -> Z^0 -> hadrons and e+ e- -> W+ W- -> hadrons. Results are shown with and without resonance decays, for correlations along and transverse to the thrust jet axis in these two classes of events.Comment: 30 pages, Latex, 8 figure

Prospects for Discovering Supersymmetry at the LHC

Supersymmetry is one of the best-motivated candidates for physics beyond the Standard Model that might be discovered at the LHC. There are many reasons to expect that it may appear at the TeV scale, in particular because it provides a natural cold dark matter candidate. The apparent discrepancy between the experimental measurement of g_mu - 2 and the Standard model value calculated using low-energy e+ e- data favours relatively light sparticles accessible to the LHC. A global likelihood analysis including this, other electroweak precision observables and B-decay observables suggests that the LHC might be able to discover supersymmetry with 1/fb or less of integrated luminosity. The LHC should be able to discover supersymmetry via the classic missing-energy signature, or in alternative phenomenological scenarios. The prospects for discovering supersymmetry at the LHC look very good.Comment: 8 pages, 11 figure

Comment On ``Grand Unification and Supersymmetric Threshold"

Barbieri and Hall have argued that threshold effects at the scale of grand-unification wipe out predictions on the SUSY scale, M_S. Using triviality arguments we give upper bounds on ultraheavy particles, while proton stability gives lower bounds on the mass of the higgs color-triplet. We find no useful lower bound on the $\Sigma$ supermultiplet, but if the strong coupling constant is as large as recent experiments suggest, unification in the minimal SUSY SU(5) model requires that the $Sigma$ masses be $\sim 10^{-7}M_V$ and that the color octet and weak triplet be split in mass by a factor of $\sim$100.Comment: 6 pages (revised

WMAP Data and Recent Developments in Supersymmetric Dark Matter

A brief review is given of the recent developments in the analyses of supersymmetric dark matter. Chief among these is the very accurate determination of the amount of cold dark matter in the universe from analyses using WMAP data. The implications of this data for the mSUGRA parameter space are analyzed. It is shown that the data admits solutions on the hyperbolic branch (HB) of the radiative breaking of the electroweak symmetry. A part of the hyperbolic branch lies in the so called inversion region where the LSP neutralino $\chi_1^0$ becomes essentially a pure Higgsino and degenerate with the next to the lightest neutralino $\chi_2^0$ and the light chargino $\chi_1^{\pm}$. Thus some of the conventional signals for the observation of supersymmetry at colliders (e.g., the missing energy signals) do not operate in this region. On the other hand the inversion region contains a high degree of degeneracy of $\chi_1^0$, $\chi_2^0$, $\chi_1^{\pm}$ leading to coannihilations which allow for the satisfaction of the WMAP relic density constraints deep on the hyperbolic branch. Further, an analysis of the neutralino-proton cross sections in this region reveals that this region can still be accessible to dark matter experiments in the future. Constraints from $g_{\mu}-2$ and from $B^0_s\to \mu^+\mu^-$ are discussed. Future prospects are also discussed.Comment: 15 pages Latex. Invited talk at the IV International Conference on Non-accelerator New Physics (NANP'03), Dubna, Russia, June 23-28, 200

Threshold Resummed Spectra in B -> Xu l nu Decays in NLO (I)

We evaluate thresholds resummed spectra in B -> Xu l nu decays in next-to-leading order. We present results for the distribution in E_X and in m_X^2/E_X^2, for the distribution in E_X and E_l and for the distribution in E_X, where E_X and m_X are the energy and the invariant mass of the final hadronic state Xu respectively and E_l is the energy of the charged lepton. We explicitly show that all these spectra (where there is no integration over the hadronic energy) can be directly related to the photon spectrum in B -> Xs gamma via short-distance coefficient functions.Comment: 33 pages, no figures. The section on the double distribution in the hadron and electron energies has been largely rewritten with an improved resummation scheme. Small stylistic changes in the remaining sections. References adde

Revisiting the Higgs Mass and Dark Matter in the CMSSM

Taking into account the available accelerator and astrophysical constraints, the mass of the lightest neutral Higgs boson h in the minimal supersymmetric extension of the Standard Model with universal soft supersymmetry-breaking masses (CMSSM) has been estimated to lie between 114 and ~ 130 GeV. Recent data from ATLAS and CMS hint that m_h ~ 125 GeV, though m_h ~ 119 GeV may still be a possibility. Here we study the consequences for the parameters of the CMSSM and direct dark matter detection if the Higgs hint is confirmed, focusing on the strips in the (m_1/2, m_0) planes for different tan beta and A_0 where the relic density of the lightest neutralino chi falls within the range of the cosmological cold dark matter density allowed by WMAP and other experiments. We find that if m_h ~ 125 GeV focus-point strips would be disfavoured, as would the low-tan beta stau-chi and stop -chi coannihilation strips, whereas the stau-chi coannihilation strip at large tan beta and A_0 > 0 would be favoured, together with its extension to a funnel where rapid annihilation via direct-channel H/A poles dominates. On the other hand, if m_h ~ 119 GeV more options would be open. We give parametrizations of WMAP strips with large tan beta and fixed A_0/m_0 > 0 that include portions compatible with m_h = 125 GeV, and present predictions for spin-independent elastic dark matter scattering along these strips. These are generally low for models compatible with m_h = 125 GeV, whereas the XENON100 experiment already excludes some portions of strips where m_h is smaller.Comment: 24 pages, 9 figure

Ab-initio angle and energy resolved photoelectron spectroscopy with time-dependent density-functional theory

We present a time-dependent density-functional method able to describe the photoelectron spectrum of atoms and molecules when excited by laser pulses. This computationally feasible scheme is based on a geometrical partitioning that efficiently gives access to photoelectron spectroscopy in time-dependent density-functional calculations. By using a geometrical approach, we provide a simple description of momentum-resolved photoe- mission including multi-photon effects. The approach is validated by comparison with results in the literature and exact calculations. Furthermore, we present numerical photoelectron angular distributions for randomly oriented nitrogen molecules in a short near infrared intense laser pulse and helium-(I) angular spectra for aligned carbon monoxide and benzene.Comment: Accepted for publication on Phys. Rev.

What if Supersymmetry Breaking Unifies beyond the GUT Scale?

We study models in which soft supersymmetry-breaking parameters of the MSSM become universal at some unification scale, $M_{in}$, above the GUT scale, \mgut. We assume that the scalar masses and gaugino masses have common values, $m_0$ and $m_{1/2}$ respectively, at $M_{in}$. We use the renormalization-group equations of the minimal supersymmetric SU(5) GUT to evaluate their evolutions down to \mgut, studying their dependences on the unknown parameters of the SU(5) superpotential. After displaying some generic examples of the evolutions of the soft supersymmetry-breaking parameters, we discuss the effects on physical sparticle masses in some specific examples. We note, for example, that near-degeneracy between the lightest neutralino and the lighter stau is progressively disfavoured as $M_{in}$ increases. This has the consequence, as we show in $(m_{1/2}, m_0)$ planes for several different values of $\tan \beta$, that the stau coannihilation region shrinks as $M_{in}$ increases, and we delineate the regions of the $(M_{in}, \tan \beta)$ plane where it is absent altogether. Moreover, as $M_{in}$ increases, the focus-point region recedes to larger values of $m_0$ for any fixed $\tan \beta$ and $m_{1/2}$. We conclude that the regions of the $(m_{1/2}, m_0)$ plane that are commonly favoured in phenomenological analyses tend to disappear at large $M_{in}$.Comment: 24 pages with 11 eps figures; references added, some figures corrected, discussion extended and figure added; version to appear in EPJ

Supersymmetric Benchmarks with Non-Universal Scalar Masses or Gravitino Dark Matter

We propose and examine a new set of benchmark supersymmetric scenarios, some of which have non-universal Higgs scalar masses (NUHM) and others have gravitino dark matter (GDM). The scalar masses in these models are either considerably larger or smaller than the narrow range allowed for the same gaugino mass m_{1/2} in the constrained MSSM (CMSSM) with universal scalar masses m_0 and neutralino dark matter. The NUHM and GDM models with larger m_0 may have large branching ratios for Higgs and/or $Z$ production in the cascade decays of heavier sparticles, whose detection we discuss. The phenomenology of the GDM models depends on the nature of the next-to-lightest supersymmetric particle (NLSP), which has a lifetime exceeding 10^4 seconds in the proposed benchmark scenarios. In one GDM scenario the NLSP is the lightest neutralino \chi, and the supersymmetric collider signatures are similar to those in previous CMSSM benchmarks, but with a distinctive spectrum. In the other GDM scenarios based on minimal supergravity (mSUGRA), the NLSP is the lighter stau slepton {\tilde \tau}_1, with a lifetime between ~ 10^4 and 3 X 10^6 seconds. Every supersymmetric cascade would end in a {\tilde \tau}_1, which would have a distinctive time-of-flight signature. Slow-moving {\tilde \tau}_1's might be trapped in a collider detector or outside it, and the preferred detection strategy would depend on the {\tilde \tau}_1 lifetime. We discuss the extent to which these mSUGRA GDM scenarios could be distinguished from gauge-mediated models.Comment: 52 pages LaTeX, 13 figure