344 research outputs found

### More on softly broken N=2 QCD

We extend previous work on the soft breaking of $N=2$ supersymmetric QCD. We
present the formalism for the breaking due to a dilaton spurion for a general
gauge group and obtain the exact effective potential. We obtain some general
features of the vacuum structure in the pure $SU(N)$ Yang-Mills theory and we
also derive a general mass formula for this class of theories, in particular we
present explicit results for the mass spectrum in the $SU(2)$ case. Finally we
analyze the vacuum structure of the $SU(2)$ theory with one massless
hypermultiplet. This theory presents dyon condensation and a first order phase
transition in the supersymmetry breaking parameter driven by non-mutually local
BPS states. This could be a hint of Argyres-Douglas-like phases in
non-supersymmetric gauge theories.Comment: 35 pages, 9 Postscript figure

### Generalized Dirichlet Branes and Zero-modes

We investigate the effective dynamics of an arbitrary Dirichlet p-brane, in a
path-integral formalism, by incorporating the massless excitations of closed
string modes in open bosonic string theory. It is shown that the closed string
background fields in the bosonic sector of type II theories induce invariant
extrinsic curvature on the world-volume. In addition, the curvature can be seen
to be associated with a divergence at the boundary of string world-sheet. The
re-normalization of the collective coordinates, next to leading order in its
derivative expansion, is performed to handle the divergence and the effective
dynamics is encoded in Dirac-Born-Infeld action. Furthermore, the collective
dynamics is generalized to include appropriate fermionic partners in type I
super-string theory. The role of string modes is reviewed in terms of the
collective coordinates and the gauge theory on the world-volume is argued to be
non-local in presence of the U(1) invariant field strength.Comment: LaTex, 20 pages, v2: minor changes and added references v3:typos
corrected, some statements are clarified in the context of zero-mode

### Some Global Aspects of Duality is String Theory

We explore some of the global aspects of duality transformations in String
Theory and Field Theory. We analyze in some detail the equivalence of dual
models corresponding to different topologies at the level of the partition
function and in terms of the operator correspondence for abelian duality. We
analyze the behavior of the cosmological constant under these transformations.
We also explore several examples of non-abelian duality where the classical
background interpretation can be maintained for the original and the dual
theories. In particular we construct a non-abelian dual of $SL(2,R)$ which
turns out to be a three-dimensional black holeComment: 31pp. One figure available upon request. CERN-TH-6991/6

### Topics in String Theory and Quantum Gravity

These are the lecture notes for the Les Houches Summer School on Quantum
Gravity held in July 1992. The notes present some general critical assessment
of other (non-string) approaches to quantum gravity, and a selected set of
topics concerning what we have learned so far about the subject from string
theory. Since these lectures are long (133 A4 pages), we include in this
abstract the table of contents, which should help the user of the bulletin
board in deciding whether to latex and print the full file.
1-FIELD THEORETICAL APPROACH TO QUANTUM GRAVITY: Linearized gravity;
Supergravity; Kaluza-Klein theories; Quantum field theory and classical
gravity; Euclidean approach to Quantum Gravity; Canonical quantization of
gravity; Gravitational Instantons.
2-CONSISTENCY CONDITIONS: ANOMALIES: Generalities about anomalies; Spinors in
2n dimensions; When can we expect to find anomalies?; The Atiyah-Singer Index
Theorem and the computation of anomalies; Examples: Green-Schwarz cancellation
mechanism and Witten's SU(2) global anomaly.
3-STRING THEORY I. BOSONIC STRING: Bosonic string; Conformal Field Theory;
Quantization of the bosonic string; Interaction in string theory and the
characterization of the moduli space; Bosonic strings with background fields.
Stringy corrections to Einstein equations; Toroidal compactifications.
$R$-duality; Operator formalism
4-STRING THEORY II. FERMIONIC STRINGS: Fermionic String; Heterotic String;
Strings at finite temperature; Is string theory finite?
5-OTHER DEVELOPMENTS AND CONCLUSIONS: String ``Phenomenology''; Black Holes
and Related SubjectsComment: 133 pages, 22 figures (not included, available upon request), LaTe

### Comments on Noncommutative Field Theories

We discuss some aspects of noncommutative quantum field theories obtained
from the Seiberg-Witten limit of string theories in the presence of an external
B-field. General properties of these theories are studied as well as the
phenomenological potential of noncommutative QED.Comment: 15 pages. Based on talks at the 9th Adriatic Meeting (Dubrovnik,
Croatia) and at String Phenomenology 2003 (Durham, UK). v2 references adde

### Remarks on Time-Space Noncommutative Field Theories

We propose a physical interpretation of the perturbative breakdown of
unitarity in time-like noncommutative field theories in terms of production of
tachyonic particles. These particles may be viewed as a remnant of a continuous
spectrum of undecoupled closed-string modes. In this way, we give a unified
view of the string-theoretical and the field-theoretical no-go arguments
against time-like noncommutative theories. We also perform a quantitative study
of various locality and causality properties of noncommutative field theories
at the quantum level.Comment: 19 pages, LaTe

### Superloop Equations and Two Dimensional Supergravity

We propose a discrete model whose continuum limit reproduces the string
susceptibility and the scaling dimensions of $(2,4m)$-minimal superconformal
models coupled to $2D$-supergravity. The basic assumption in our presentation
is a set of super-Virasoro constraints imposed on the partition function. We
recover the Neveu-Schwarz and Ramond sectors of the theory, and we are also
able to evaluate all planar loop correlation functions in the continuum limit.
We find evidence to identify the integrable hierarchy of non-linear equations
describing the double scaling limit as a supersymmetric generalization of KP
studied by Rabin.Comment: 34 page

### Direct T-violation measurements and T-odd effects in decay experiments

Motivated by the recent experimental announcements for direct measurements of
time-reversal non-invariance in the neutral kaon system, we make a comparative
discussion of the CPLEAR and KTeV measurements. The most suitable way to
consistently incorporate the mixing, the time evolution and the decays of
kaons, is to describe the neutral kaon system as a system with a non-Hermitean
Hamiltonian. In this framework, the physical (decaying) incoming and outgoing
states are distinct and belong to dual spaces. Moreover, since they are
eigenstates of the full Hamiltonian, they never oscillate. This is directly
manifest in the orthogonality conditions of the physical states, which entirely
determine the evolution of the kaon system. Along these lines we conclude:
CPLEAR studies K0-bar{K0} oscillations, a process where initial and final
states can be reversed, the CPLEAR asymmetry being an effect directly related
to the definition of time-reversal. Conclusively, CPLEAR provides a direct
measurement of T-violation without any assumption either on unitarity or on
CPT-invariance. The KTeV experiment studies in particular the process KL -> pi+
pi- e+ e- where they measure a T-odd effect. However, using unitarity together
with estimates of the final state interactions, it should be possible to
determine whether this effect can be identified with a genuine T-reversal
violation.Comment: 11 pages, no figures. Presented at the 34th Rencontres de Moriond on
Electroweak Interactions and Unified Theories, Les Arcs, 13-20 March, 199

### Powering AGNs with super-critical black holes

We propose a novel mechanism for powering the central engines of Active
Galactic Nuclei through super-critical (type II) black hole collapse. In this
picture, ~$10^3 M_\odot$ of material collapsing at relativistic speeds can
trigger a gravitational shock, which can eject a large percentage of the
collapsing matter at relativistic speeds, leaving behind a "light" black hole.
In the presence of a poloidal magnetic field, the plasma collimates along two
jets, and the associated electron synchrotron radiation can easily account for
the observed radio luminosities, sizes and durations of AGN jets. For Lorentz
factors of order 100 and magnetic fields of a few hundred $\mu G$, synchrotron
electrons can shine for $10^6$ yrs, producing jets of sizes of order 100 kpc.
This mechanism may also be relevant for Gamma Ray Bursts and, in the absence of
magnetic field, supernova explosions.Comment: 4 pages, 1 figur

### Space-time noncommutativity and (1+1) Higgs Model

We compare the classical scattering of kinks in (1+1) Higgs model with its
analogous noncommutative counterpart. While at a classical level we are able to
solve the scattering at all orders finding a smooth solution, at a
noncommutative level we present only perturbative results, suggesting the
existence of a smooth solution also in this case.Comment: 18 pages, 2 figure

- â€¦