Nature of Microscopic Black Holes and Gravity in Theories with Particle Species

Relying solely on unitarity and the consistency with large-distance black hole physics, we derive model-independent properties of the microscopic black holes and of short-distance gravity in theories with N particle species. In this class of theories black holes can be as light as M_{Planck}/\sqrt{N} and be produced in particle collisions above this energy. We show, that the micro black holes must come in the same variety as the species do, although their label is not associated with any conserved charge measurable at large distances. In contrast with big Schwarzschildian ones, the evaporation of the smallest black holes is maximally undemocratic and is biased in favor of particular species. With an increasing mass the democracy characteristic to the usual macro black holes is gradually regained. The lowest possible mass above which black holes become Einsteinian is \sqrt{N} M_{Planck}. This fact uncovers the new fundamental scale (below the quantum gravity scale) above which gravity changes classically, and the properties of black holes and gravity are such as if some extra dimensions open up, although no such input exists in the theory. Our observations indicate that geometry of space may be an emergent concept following from large number of species and the consistency with macro black hole physics. We apply our findings to the phenomenological properties of the micro black holes that can be observed at LHC for large N. Extrapolating our findings to small N, one may ask whether the existence of quark and lepton flavors is already an evidence for emergent extra dimensions at short distances.Comment: 14 page

A supersymmetric matrix model: II. Exploring higher-fermion-number sectors

Continuing our previous analysis of a supersymmetric quantum-mechanical matrix model, we study in detail the properties of its sectors with fermion number F=2 and 3. We confirm all previous expectations, modulo the appearance, at strong coupling, of {\it two} new bosonic ground states causing a further jump in Witten's index across a previously identified critical 't Hooft coupling $\lambda_c$. We are able to elucidate the origin of these new SUSY vacua by considering the $\lambda \to \infty$ limit and a strong coupling expansion around it.Comment: 14 pages, 4 figure

String Cosmology: Basic Ideas and General Results

After recalling a few basic concepts from cosmology and string theory, I will outline the main ideas/assumptions underlying (our own group's approach to) string cosmology and show how these lead to the definition of a two-parameter family of ``minimal" models. I will then briefly explain how to compute, in terms of those parameters, the spectrum of scalar, tensor and electromagnetic perturbations, and mention their most relevant physical consequences. More details on the latter part of this talk can be found in Maurizio Gasperini's contribution to these proceedings.Comment: Latex file + 3 figures. Talk presented at the 3rd Colloque Cosmologie, Paris, 7-9 June 9

Pre-bangian origin of our entropy and time arrow

I argue that, in the chaotic version of string cosmology proposed recently, classical and quantum effects generate, at the time of exit to radiation, the correct amount of entropy to saturate a Hubble (or holography) entropy bound (HEB) and to identify, within our own Universe, the arrow of time. Demanding that the HEB be fulfilled at all times forces a crucial "branch change" to occur, and the so-called string phase to end at a critical value of the effective Planck mass, in agreement with previous conjectures.Comment: Latex file, 8 pages, 1 Figur

A Simple/Short Introduction to Pre-Big-Bang Physics/Cosmology

A simple, non-technical introduction to the pre-big bang scenario is given, emphasizing physical motivations, considerations, and consequences over formalism.Comment: 15 pages, macros included, 4 figures, lecture presented at the Erice School of Subnuclear Physics, 35th Course "Highlights: 50 Years Later", Erice, Italy, August 26-September 4, 1997 revised version, references updated, fig. 3 more precisely describe

Quantum hair and the string-black hole correspondence

We consider a thought experiment in which an energetic massless string probes a "stringhole" (a heavy string lying on the correspondence curve between strings and black holes) at large enough impact parameter for the regime to be under theoretical control. The corresponding, explicitly unitary, $S$-matrix turns out to be perturbatively sensitive to the microstate of the stringhole: in particular, at leading order in $l_s/b$, it depends on a projection of the stringhole's Lorentz-contracted quadrupole moment. The string-black hole correspondence is therefore violated if one assumes quantum hair to be exponentially suppressed as a function of black-hole entropy. Implications for the information paradox are briefly discussed.Comment: 11 pages, no figures, typos corrected, discussion and references added, version accepted for publication in Class. and Quantum Gravit

The emergence of noun and verb categories in the acquisition of French

This paper considers whether the child's early vocabulary shows signs of being organized into word categories. Two main kinds of evidence are looked for: 1. differential production of fillers (referred to here more neutrally as Prefixed Additional Elements); ii. relevant phonomoprhological variation for verb-words, and only in them. Results of analyses of natural speech production provided by the longitudinal studies of two French acquiring children followed between the ages of 1;3 and 2;3, show that there is a first period in which words seem to constitute one, formally undifferentiated, set. Differentiation between noun-words and verb-words appears progressively, as evidenced by the differential occurrence of PAEs in prenominal and in preverbal positions, and in the appearance of phonomorphologically relevant variations only in words that are verbs in the language. Looking at connected aspects of language, other péhenomena are observed to occur at the same time, in particular, a significant increase in the production of multiword speech, that becomes the dominant way of expression

Inflating, Warming Up, and Probing the Pre-Bangian Universe

Classical and quantum gravitational instabilities, can, respectively, inflate and warm up a primordial Universe satisfying a superstring-motivated principle of "Asymptotic Past Triviality". A physically viable big bang is thus generated without invoking either large fine-tunings or a long period of post-big bang inflation. Properties of the pre-bangian Universe can be probed through its observable relics, which include: i) a (possibly observable) stochastic gravitational-wave background; ii) a (possible) new mechanism for seeding the galactic magnetic fields; iii) a (possible) new source of large-scale structure and CMB anisotropy.Comment: Latex file, 17 pages, 5 figures, Based on two recent talks, References update

String Cosmology: Concepts and Consequences

After recalling a few basic concepts from cosmology and string theory, I will discuss the main ideas/assumptions underlying string cosmology and show how these lead to a two-parameter family of ``minimal" models. I will then explain how to compute, in terms of those parameters, the spectrum of scalar, tensor and electromagnetic perturbations, point at their ($T$ and $S$-type) duality symmetries, and mention their most relevant physical consequences.Comment: 21p, latex, epsf, 3 figures in uuencoded fil