STRING by stariya

VIEWS: 5 PAGES: 4

									AREA 3. - STRING THEORY AND QUATUM GRAVITY

The discovery of D-branes as non-perturbative states of string theory has opened the
way to use string theory to describe the gauge theory living on their world-volume.
This is possible thanks to the two-fold nature of D-branes to be, on the one hand, a
classical solution of the low-energy effective action containing closed strings and, on
the other one, to support a gauge theory on their world-volume due to the open
strings attached to it. Supegravity solutions encode the dual gauge theory both in
non-perturbative and perturbative regimes. It has been shown that quantum
properties such as the chiral and scale anomalies of supersymmetric and non-
conformal theories living on D-branes can be obtained from their corresponding
classical supergravity solution. In particular, in previous works, a bound state of
fractional D3-branes localized inside the world-volume of fractional D7-branes in the
orbifolds C^2/Z_2 and C^3/(Z_2xZ_2) has been studied. For a suitable number of
D3 and D7 branes and by using the corresponding supergravity solution, the super
QCD N=2 and N=1 scale and chiral anomalies have been reproduced. It has been
given an explanation of the beautiful working of the gauge/gravity correspondence in
Type IIB superstring theory by computing the "annulus" diagram corresponding to
the interaction of a fractional D3 brane with a gauge field turned-on on its world
volume and a "stack" of N D3 fractional branes embedded in the orbifolds C^2/Z_2
and C^3/(Z_2xZ_2). It has been shown that the logarithmic divergence exhibited by
this amplitude can be equivalently read as due to the massless open string states
circulating in the loop or to the massless closed string states exchanged between the
branes. This, in turn, follows from the fact that, by performing a suitable conformal
transformation which sends the open into closed string (open/closed string duality),
the contribution of the massless open string states is mapped into the one of the
closed string states, while the contribution of the massive states (threshold
corrections) is vanishing. Hence the reasons why perturbative properties of many
gauge theories living on non-conformal and with reduced supersymmetry branes are
reproduced from their corresponding supergravity solution lie in the open/closed
string duality and in the vanishing thresholds.


Activity 3.1 - string theory and gauge/gravity correspondance
A. Liccardo, R. Marotta, R. Musto, F. Nicodemi, R. Pettorino, F. Pezzella

It has been explored the role of supersymmetry in the working of the gauge/gravity
correspondence. To this aim Type O string theory and its orientifold have been taken
in exam. In so doing, it has been obtained a realization in terms of branes of the so-
called "orientifold field theories". These are non supersymmetric gauge theories
having the same bosonic sector as Super Yang-Mills N=4,2,1 theories according to
the chosen orientifold. In particular, one of the most interesting results has been the
derivation of QCD with three colours as world-volume theory of a certain brane
configuration. From the analysis of such models it has been obtained the result that
the gauge/gravity correspondence is not a property peculiar of supersymmetric
models, as Type IIB, but it holds as well in non-supersymmetric models when, also
in this case, threshold corrections vanish. It has been understood that such a
condition is satisfied when the massive states in the string models taken in exam are
arranged as "short" multiplets of supersymmetric gauge theories N=4.


Program for 2005
A natural development of the research activity until now followed consists in
establishing a connection between our results in the framework of the gauge/gravity
correspondence and those one can find in literature obtained through the duality seen
as a geometrical transition.
In this approach gauge theories have been obtained as world-volume theories of
branes wrapped on cycles of "resolved" Calabi-Yau manifolds. They admit a "dual"
description in which branes disappear and are substituted by fluxes of suitable
supergravity fields through "blown-up" 3-cycles. This kind of duality has allowed to
get the non-perturbative effective superpotential of N=1 gauge theories, like the
Veneziano-Yankielowicz or Affleck-Dine-Seiberg superpotentials. Our future task
will be to explore the relations between gauge/gravity correspondence and
geometrical transitions in supersymmetric and non-supersymmetric string models,
within the
supersymmetric (with N=1 matter) and non-supersymmetric (orientifold field
theories) previously considered. Starting from gravity or supergravity "deformed"
geometries also caracterized by a non constant dilaton field, the aim of this activity is
to determine non-perturbative effects of gauge theories, such as their corresponding
superpotential.
Finally, our research project foresees also to study gauge theories interesting from a
phenomenological point of view that live on the world-volume of intersecting branes.
In particular, our attention will be focused on perturbative and non-perturbative
aspects of gauge theories by using the techniques of the open/closed string duality
already developed in the case of parallel branes.


Activity 3.2 - ADS/CFT correspondance
W. Mueck

The AdS/CFT correpondence is an important and modern tool to study aspects of
gauge theories at coupling regimes that are not accessibly by ordinary perturbation
theory. It is a holographic duality and builds on the fact that the dynamics of a given
Supergravity theory on an (asymptotically) bulk anti-de Sitter space encodes the
correlation functions of a certain (deformed) conformal field theory, which is known
as its dual theory. There exists a precise method, known as Holographic
Renormalization, that extracts the information relevant for the correlators from the
bulk dynamics. A systematic and efficient method of Holographic Renormalization
using the Hamilton-Jacobi approach has been developed and provides the basis of the
holographic calculation of correlation functions in conformal gauge theories. The
study of correlation functions in the so-called Holographic Renormalization Group
(RG) flows, which are the duals of conformal field theories deformed by operator
insertions or non-zero vacuum expectation values, is of great interest, because the
RG flows include realistic phenomena, such as confinement. The technically
challenging study of fluctuations in the bulk background configurations of interest
has led to important results for two-point functions. However, the difficulties caused
a halt in the research and literature on the topic, and most three-point functions were
considered out-of-reach for present-day calculational methods. A gauge-invariant
formalism for the treatment of fluctuations in Holographic RG flow backgrounds was
developed, which elegantly removes the difficulties encountered previously . By
using this formalism they have been computed the 3-point functions in a generic
holographic GR flux. As a relevant application it has been considered the Girardello-
Petrini-Porrati-Zaffaroni flux for which gluball scattering amplitudes have been
computed. Such amplitudes imply selection rules for glueball decays which are not
yet explained in the framework of Quantum Field Theories.


Program for 2005

As a future program our aim is to generalize the computation of correlators in field
theory through their respective dual in cases which are not asymptotically anti-de
Sitter. These are just more relevant and there are some already well-known, as the
Klebanov-Strassler and Maldacenza-Nunez solutions. Now-a-day it is not known
how the supergravity dynamics encodes the correlation functions of the dual theory
in these cases but a general formulation of the gauge-invariant formalism is an
important step because it is applicable directly to the analysis of the gravity
fluctuations. Once solved the bulk dynamics, it remains to establish the precise
correspondence between gauge operators and bulk fields.


Activity 3.3 - Statistical mechanics
A. Coniglio, A. Caiazzo, A. de Candia, F. di Liberto, A. Fierro, M. Nicodemi, F. Peruggi, P. Ruggiero,
M. Pica Ciamarra, M. Tarzia, T. Abete

Our main research lines concern the physics of complex, disordered and glassy
systems; granular media; soft matter; systems of biological interest. Such research
lines are supported by national and international grants (EU, PRIN, FIRB,
Regione,Ministero Affari Esteri).
Our group is part of the "Laboratorio di Modellistica del Centro Regionale di
Competenza AMRA", where we are also responsible for a 198 processor cluster.

Main international collaborations are with:
ESPCI in Paris and CNRS in Rennes, on granular media;
Imperial College London on off-equilibrium systems;
CNRS Montpelier and ESPCI in Paris on soft-matter;
Saclay on biological systems.

New scientific activities.
Our team is involved in the development of "Distretto Tecnologico sui Materiali
Polimerici e Compositi Strutturali della Campania".
We have started a new research line on the applications of Statistical Mechanics to
biophysics and bioinformatics.


Activity 3.4. - Glass transition
A. Caiazzo, A. Coniglio,A.de Candia,F. di Liberto A. Fierro, M. Nicodemi, M. Tarzia


Theoretical model for glass transition
We developed a model with self-generated disorder and local frustration which
reproduces many features of glassy systems, in particular a dynamical transition is
found satisfying the predictions of the mode coupling theory for supercooled liquids.

Attractive glass
We also introduced a generalized p-spin glass like model that captures some of the
main features of attractive glasses (recently found by Mode Coupling investigations
of attractive colloids) such as a glass/glass transition line and dynamical singularity
points characterized by a logarithmic time dependence of the relaxation.

Program for 2005

We will investigate its features not predicted by the Mode Coupling scenario that
could further describe the attractive glasses behavior, such as aging effects with new
dynamical singularity points ruled by logarithmic laws or the presence of a glass
spinodal line.


Activity 3.5 - Granular media
A. Coniglio, A. Fierro, M. Nicodemi, M. Pica Ciamarra,M. Tarzia

We have investigated by means of computer simulations (monte-carlo and molecular
dynamics         simulations), and mean field analytical approximations, two relevant
questions rised by granular materials. The understanding of flowing grains, and the
possibility of describing granular materials in a statistical mechanics framework.

We have compared analytically, in mean field, the predictions of two different
statistical mechanics approaches proposed to describe binary granular mixtures
subjected to some external driving (continuous shaking or tap dynamics). Focusing
on the phenomenon of size segregation, we have found that the two approaches give
different predictions of the crossovers from BNE to RBNE with respect to the
shaking amplitude, which could be detected experimentally.

Program for 2005

We plan to investigate flowing grains, and particularly the role of dynamical
instabilities in granular flow; and systems subject to a tap dynamics. Here we want to
test Edward's statistical mechanics approach to granular media. Particularly we want
to demonstarte the existence of phase transitions in granular mixtures, predicted by
our mean filed calculations, via computer simulations.

Our future research project concerns the study of the nature of the size segregation in
granular mixtures. Introducing a mean field theory in the framework of a statistical
mechanics approach for athermal systems, and by means of numerical simulations,
we will study a new purely thermodynamic mechanism which gives rise to the size
segregation phenomenon, which might be induced by a true phase transition.

								
To top