24,020 research outputs found
Thermal effects in perturbative noncommutative gauge theories
The thermodynamics of gauge theories on the noncommutative plane is studied
in perturbation theory. For U(1) noncommutative Yang-Mills we compute the first
quantum correction to the ideal gas free energy density and study their
behavior in the low and high temperature regimes. Since the noncommutativity
scale effectively cutoff interactions at large distances, the theory is regular
in the infrared. In the case of U(N) noncommutative Yang-Mills we evaluate the
two-loop free energy density and find that it depends on the noncommutativity
parameter through the contribution of non-planar diagrams.Comment: 15 pages, harvmac. Minor changes with respect to v2. Footnote
expanded, remark added in Section 3, typos corrected and references added.
Final version to be published in JHE
Ferromagnetic ordering in graphs with arbitrary degree distribution
We present a detailed study of the phase diagram of the Ising model in random
graphs with arbitrary degree distribution. By using the replica method we
compute exactly the value of the critical temperature and the associated
critical exponents as a function of the minimum and maximum degree, and the
degree distribution characterizing the graph. As expected, there is a
ferromagnetic transition provided < \infty. However, if the fourth
moment of the degree distribution is not finite then non-trivial scaling
exponents are obtained. These results are analyzed for the particular case of
power-law distributed random graphs.Comment: 9 pages, 1 figur
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
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.
-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
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