Black holes from high-energy beam--beam collisions

Using a recent technique, proposed by Eardley and Giddings, we extend their results to the high-energy collision of two beams of massless particles, i.e. of two finite-front shock waves. Closed (marginally) trapped surfaces can be determined analytically in several cases even for collisions at non-vanishing impact parameter in D\ge 4 space-time dimensions. We are able to confirm and extend earlier conjectures by Yurtsever, and to deal with arbitrary axisymmetric profiles, including an amusing case of ``fractal'' beams. We finally discuss some implications of our results in high-energy experiments and in cosmology.Comment: 17 pages Revtex, 1 figure, references adde

Leukocyte telomere shortening in Huntington's disease

Huntington's disease (HD) is an autosomal dominant neurodegenerative disease caused by an expanded CAG repeat. Though symptom onset commonly occurs at midlife and inversely correlates with the CAG repeat expansion, age at clinical onset and progression rate are variable. In the present study we investigated the relationship between leukocyte telomere length (LTL) and HD development. LTL was measured by real-time PCR in manifest HD patients (HD, n = 62), pre-manifest HD patients (pre-HD, n = 38), and age-matched controls (n = 76). Significant LTL differences were observed between the three groups (p < .0001), with LTL values in the order: HD < pre-HD < controls. The relationship between LTL and age was different in the three groups. An inverse relationship between mean LTL and CAG repeat number was found in the pre-HD (p = .03). The overall data seem to indicate that after age 30 years, LT begins to shorten markedly in pre-HD patients according to CAG number and increasing age, up to the values observed in HD. This very suggestive picture allowed us to hypothesize that in pre-manifest HD, LTL could be a measure of time to clinical HD onset. The possible use of LTL as a reliable biomarker to track HD development and progression was evaluated and discussed

Estimating Diffractive Higgs Boson Production at LHC from HERA Data

Using a recently proposed factorization hypothesis for semi-inclusive hard processes in QCD, one can study, in principle, the diffractive production of the Standard Model Higgs boson at LHC using only, as input, $ep$ diffractive hard-processes data of the type recently collected and analyzed by the H1 and ZEUS collaborations at HERA. While waiting for a more precise and complete set of data, we combine here the existing data with a simple Pomeron-exchange picture and find a large spread in the Higgs boson production cross section, depending on the input parametrization of the Pomeron's parton content. In particular, if the Pomeron gluon density $f_{g/P}(\beta)$ is peaked at large $\beta$ for small scales, single diffractive events will represent a sizeable fraction of all produced Higgs bosons with an expected better-than-average signal-to-background ratio.Comment: 12 pages (LATEX); figures are included via epsfig; the corresponding postscript files are uuencoded. A style file derived from the ``elsart.sty'' is included, as well as the ``elsart12.sty'' file. The AMSTEX fonts are required. See http://surya11.cern.ch/users/graudenz/publications.html for a complete postscript fil

A Model for the Big Bounce

I motivate a proposal for modeling, at weak string coupling, the ``Big Bounce" transition from a growing-curvature phase to standard (FRW) cosmology in terms of a pressure-less dense gas of "string-holes" (SH), string states lying on the correspondence curve between strings and black holes. During this phase SH evolve in such a way that temperature and (string-frame) curvature remain $O(M_s)$ and (a cosmological version of) the holographic entropy bound remains saturated. This reasoning also appears to imply a new interpretation of the Hagedorn phase transition in string theory.Comment: 10 pages, 2 figure

Resonant decay of parity odd bubbles in hot hadronic matter

We investigate the decay of metastable states with broken CP-symmetry which have recently been proposed by Kharzeev, Pisarski and Tytgat to form in hot hadronic matter. We consider the efficiency of the amplification of the $\eta'$-field via parametric resonance, taking the backreaction into account. For times of the order $t\approx 10 fm$, we find a particle density of about $0.7/fm^3$ and a correlation length of $\xi_{max}\approx 2.5 fm$. The corresponding momentum spectra show a non-thermal behaviour.Comment: 11 pages latex file with 4 gif - figures. Uses elsart.cls (included

Radiation Problem in Transplanckian Scattering

We investigate hard radiation emission in small-angle transplanckian scattering. We show how to reduce this problem to a quantum field theory computation in a classical background (gravitational shock wave). In momentum space, the formalism is similar to the flat-space light cone perturbation theory, with shock wave crossing vertices added. In the impact parameter representation, the radiating particle splits into a multi-particle virtual state, whose wavefunction is then multiplied by individual eikonal factors. As a phenomenological application, we study QCD radiation in transplanckian collisions of TeV-scale gravity models. We derive the distribution of initial state radiation gluons, and find a suppression at large transverse momenta with respect to the standard QCD result. This is due to rescattering events, in which the quark and the emitted gluon scatter coherently. Interestingly, the suppression factor depends on the number of extra dimensions and provides a new experimental handle to measure this number. We evaluate the leading-log corrections to partonic cross-sections due to the initial state radiation, and prove that they can be absorbed into the hadronic PDF. The factorization scale should then be chosen in agreement with an earlier proposal of Emparan, Masip, and Rattazzi. In the future, our methods can be applied to the gravitational radiation in transplanckian scattering, where they can go beyond the existing approaches limited to the soft radiation case.Comment: 41 pp, v2: minor changes and added refs, conforms with published versio

Microscopic unitary description of tidal excitations in high-energy string-brane collisions

The eikonal operator was originally introduced to describe the effect of tidal excitations on higher-genus elastic string amplitudes at high energy. In this paper we provide a precise interpretation for this operator through the explicit tree-level calculation of generic inelastic transitions between closed strings as they scatter off a stack of parallel Dp-branes. We perform this analysis both in the light-cone gauge, using the Green-Schwarz vertex, and in the covariant formalism, using the Reggeon vertex operator. We also present a detailed discussion of the high energy behaviour of the covariant string amplitudes, showing how to take into account the energy factors that enhance the contribution of the longitudinally polarized massive states in a simple way.Comment: 58 page

Singularity structure in Veneziano's model

We consider the structure of the cosmological singularity in Veneziano's inflationary model. The problem of choosing initial data in the model is shown to be unsolved -- the spacetime in the asymptotically flat limit can be filled with an arbitrary number of gravitational and scalar field quanta. As a result, the universe acquires a domain structure near the singularity, with an anisotropic expansion of its own being realized in each domain.Comment: 16 pages, 2 figures, shorter then journal version; references added, discussion slightly expande

Infinite statistics, symmetry breaking and combinatorial hierarchy

The physics of symmetry breaking in theories with strongly interacting quanta obeying infinite (quantum Boltzmann) statistics known as quons is discussed. The picture of Bose/Fermi particles as low energy excitations over nontrivial quon condensate is advocated. Using induced gravity arguments it is demonstrated that the Planck mass in such low energy effective theory can be factorially (in number of degrees of freedom) larger than its true ultraviolet cutoff. Thus, the assumption that statistics of relevant high energy excitations is neither Bose nor Fermi but infinite can remove the hierarchy problem without necessity to introduce any artificially large numbers. Quantum mechanical model illustrating this scenario is presented.Comment: LaTeX, 11 page

Can Gluons Trace Baryon Number?

QCD as a gauge non-Abelian theory imposes severe constraints on the structure of the baryon wave function. We point out that, contrary to a widely accepted belief, the traces of baryon number in a high-energy process can reside in a non-perturbative configuration of gluon fields, rather than in the valence quarks. We argue that this conjecture can be tested experimentally, since it can lead to substantial baryon asymmetry in the central rapidity region of ultra-relativistic nucleus-nucleus collisions.Comment: 12 pages, LaTeX, figures available upon reques