5,652 research outputs found
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 . We are able to elucidate the origin of these new SUSY
vacua by considering the limit and a strong coupling
expansion around it.Comment: 14 pages, 4 figure
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
A numerical simulation of pre-big bang cosmology
We analyse numerically the onset of pre-big bang inflation in an
inhomogeneous, spherically symmetric Universe. Adding a small dilatonic
perturbation to a trivial (Milne) background, we find that suitable regions of
space undergo dilaton-driven inflation and quickly become spatially flat
(). Numerical calculations are pushed close enough to the big
bang singularity to allow cross checks against previously proposed analytic
asymptotic solutions.Comment: 19 pages, revtex, matlab code available at
http://www.fis.unipr.it/~onofr
Supersymmetry and Combinatorics
We show how a recently proposed supersymmetric quantum mechanics model leads
to non-trivial results/conjectures on the combinatorics of binary necklaces and
linear-feedback shift-registers. Pauli's exclusion principle plays a crucial
role: by projecting out certain states/necklaces, it allows to represent the
supersymmetry algebra in the resulting subspace. Some of our results can be
rephrased in terms of generalizations of the well-known Witten index.Comment: 14 pages, 3 figures, text expanded, references adde
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 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
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
N=1 Super Yang-Mills on the Lattice in the Strong Coupling Limit
We study the N=1 supersymmetric SU(N) Yang-Mills theory on the lattice at
strong coupling. We analyse and discuss the recent results obtained at strong
coupling and large N for the mesonic and fermionic propagators and spectrum.Comment: Latex 3 pages. Contribution to the Lattice99 Proceeding
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
The explicit Mordell conjecture for families of curves
In this article we prove the explicit Mordell Conjecture for large families of curves. In addition, we introduce a method, of easy application, to compute all rational points on curves of quite general shape and increasing genus. The method bases on some explicit and sharp estimates for the height of such rational points, and the bounds are small enough to successfully implement a computer search. As an evidence of the simplicity of its application, we present a variety of explicit examples and explain how to produce many others. In the appendix our method is compared in detail to the classical method of Manin-Demjanenko and the analysis of our explicit examples is carried to conclusion
The eta-prime propagator in quenched QCD
The calculation of the eta-prime hairpin diagram is carried out in the
modified quenched approximation (MQA) in which the lattice artifact which
causes exceptional configurations is removed by shifting observed poles at
kappa<kappa_c in the quark propagators to the critical value of hop ping
parameter. By this method, the eta-prime propagator can be accurately
calculated even for very light quark mass. A determination of the topological
susceptibility for quenched QCD is also obtained, using the fermionic method of
Smit and Vink to calculate winding numbers.Comment: 3 pages, 3 postscript figure
- …