Found at least 20 result(s)

### 02.07.2008 (Wednesday)

#### Random-Matrix Theory within Superstatistics

Regular Seminar Adel Abul-Magd (Sinai University)

 at: 11:00 Brunel U.room M128 abstract: In analogy to Beck and Cohen's superstatistics (1), we connect the canonical Gaussian ensembles of the random-matrix theory (RMT) to their superstatistical generalizations through the fluctuation of an intensive parameter, the local density of states (2). On one hand, the superstatistical RMT, seen from the present perspective, may bear interest per se because of the additional nontrivial fluctuations introduced in a simple model. On the other hand, it may constitute a useful statistical paradigm for the analysis of the spectral fluctuations of systems with mixed regular-chaotic dynamics. In contrast to other proposals for applying RMT to mixed dynamics, the superstatistical approach yields ensemble of matrices, which are invariant with respect to base transformation. The formalism has been checked by the analysis of experimental resonance spectra of mixed microwave billiards (3). The spectra for each billiard are represented as time series in which the level order plays the role of time. Each series is shown to have two relaxation times as required by superstatistics, which involves the folding of two distribution functions. Analysis of the time series suggests that the superstatistical parameter has an inverse-chi-square distribution. The experimental distribution nearest-neighbor level spacings and strength functions agree with the corresponding predicted distributions. (1) C. Beck and E.G.D. Cohen, Physica A 322, 267 (2003). (2) A.Y. Abul-Magd, Phys.Rev. E 71, 066207 (2005). (3) A.Y. Abul-Magd, B. Dietz, T. Friedrich, and A. Richter, Phys. R

### 12.03.2008 (Wednesday)

#### Triadophilia: A Special Corner in the Landscape

Regular Seminar Yang-Hui He (Oxford University)

 at: 14:00 ICroom Huxley 503 abstract: We point out a special corner in the space of Calabi-Yau compactifications where standard-like models tend to emerge. We show how these scenarios are inter-related via a mathematical process of transgression of bundles, a generalisation of the conifold transition. Perhaps our world is special and we live in this oasis within the multitude of vacua.

### 27.02.2008 (Wednesday)

#### Killing superalgebras in supergravity

Triangular Seminar Jose Figueroa-O'Farrill (University of Edinburgh)

 at: 16:00 QMWroom LG1 abstract: I will discuss several constructions of superalgebras associated to the Killing spinors of a supergravity background, with special emphasis on the ten- and eleven-dimensional supergravities.

### 03.05.2007 (Thursday)

#### A proposal on time dependent AdS/CFT correspondence and null-singularity

Regular Seminar Chong-Sun Chu (Durham University)

 at: 13:30 ICroom Huxley 503 abstract: The understanding of the nature of spacetime singularity and whether and how it is resolved is one of the most important problem in quantum gravity. Important examples are black hole singularity and cosmological singularity in the big bang. In this talk we will be interested in the later type and an approach to the problem using AdS/CFT correspondence for time-dependent background will be discussed. Our gauge theory results suggest that spacetime singularity is indeed resolved and the mechanism will be discussed.

### 09.03.2007 (Friday)

#### Quantum Mechanics of the Doubled Torus

Regular Seminar Emily Hackett-Jones (Edinburgh)

 at: 12:00 QMWroom 112 abstract:

### 08.03.2007 (Thursday)

#### The wave function behavior of the open topological string

Regular Seminar Amir-Kian Kashani-Poor (University of Amsterdam)

 at: 13:30 ICroom Huxley 503 abstract: Suppose we could calculate the string partition function to all genera using worldsheet methods. What could we learn from this expression about a potentially underlying (non-perturbative) target space description of the theory? We address this question in the context of the open topological A-model.

### 16.11.2006 (Thursday)

#### Magnon Boundstates in Gauge/String Duality

Regular Seminar Heng-Yu Chen (DAMTP, Cambridge)

 at: 13:30 ICroom Huxley 503 abstract: I will begin with basic review on the integrabilities in AdS/CFT correspondence, and move on discussing the role of scattering matrices in gauge and string thoeries. I will then explain the formation of magnon boundststates in gauge theory and their corresponding classical string solution. The scattering of magnon boundstates and their classifications will also be discussed in this seminar. I will also mention some work in progress.

### 03.10.2006 (Tuesday)

#### Twistor Strings and Gravity

Regular Seminar Mohab Abou-Zeid (Vrije U., Brussels and Intl. Solvay Inst., Brussels)

 at: 14:00 ICroom 503 Huxley abstract: I will present a modification of the Berkovits twistor string model which gives Einstein supergravity coupled to Yang-Mills, and has a limit in which the gravity modes can be decoupled to give pure gauge theory amplitudes. I will start by reviewing a number of relevant aspects of twistor theory, including special features associated with different space-time signatures, supertwistor space, the Penrose transform, the infinity twistor and Penrose's non-linear graviton construction. I will then review the Witten and Berkovits twistor strings, with emphasis on the latter. The world-sheet formulation of the Berkovits model involves so-called beta-gamma systems, I will describe the symmetries of such systems and their gauging, and explain how the analysis can be applied to the construction of a family of new gauged Berkovits twistor strings which are free from world-sheet anomalies. I will also describe the corresponding spectra in space-time, and show that they give Einstein supergravities instead of the higher derivative conformal supergravities arising in the original twistor string models. The new theories include one with the spectrum of N = 8 supergravity, two theories with the spectrum of N = 4 supergravity coupled to N = 4 Yang-Mills, a family of N greater than 0 models with the spectra of self-dual supergravity coupled to self-dual super-Yang-Mills, and a non-supersymmetric string with the spectrum of self-dual gravity coupled to self-dual Yang-Mills and a scalar. Time permitting, I will discuss what is known about the interactions.

### 01.06.2006 (Thursday)

#### Time Dependent AdS/CFT Proposal and Spacetime Singularities

Regular Seminar Chong-Sun Chu (Durham)

 at: 14:00 QMWroom 112 abstract:

### 06.03.2006 (Monday)

#### Heterotic MSSM

Regular Seminar Yang-Hui He (Oxford)

 at: 13:30 ICroom Ballroom, 58 Princes Gate abstract: We show the existence of an N=1 supersymmetric vacuum in string theory whose observable sector has exactly the matter content of the MSSM without exotic particles and vector-like pairs of any type. This is done so by compactifying the E_8 x E_8 heterotic string on a Calabi-Yau threefold endowed with an SU(4) vector bundle which has been constructed after extensive search. In addition, we discuss the Yukawa couplings and Higgs mu-terms in this model.

### 23.02.2006 (Thursday)

#### On T-folds and Supersymmetry

Regular Seminar Emily Hackett-Jones (Edinburgh)

 at: 14:00 QMWroom 112 abstract:

### 19.01.2006 (Thursday)

#### Matrix Representation of the Combinatorics of Renormalization in Perturbative QFT

Regular Seminar Kurusch Ebrahimi-Fard (IHES)

 at: 14:00 QMWroom 112 abstract: Kreimer discovered a Hopf algebra structure underlying the combinatorics of renormalization in perturbative quantum field theory. Later, Connes and Kreimer explored the link to non-commutative geometry via a Hopf algebra of rooted trees and described a Hopf algebra of Feynman graphs. After reviewing these developments in some detail we show in this talk how to organize the combinatorics of renormalization in terms of unipotent triangular matrix representations. A simple decomposition of such matrices is used to characterize the process of renormalization. We thereby recover a matrix (anti-)representation of the Birkhoff decomposition of Connes and Kreimer.

### 06.10.2005 (Thursday)

#### Twistors, Amplitudes and Unitarity Methods

Regular Seminar Emil Bjerrum-Bohr (Swansea)

 at: 14:00 QMWroom 112 abstract:

### 05.10.2005 (Wednesday)

#### Gauged sigma models and generalised geometry

Triangular Seminar Jose Figueroa-O'Farrill (Edinburgh)

 at: 15:00 QMWroom 410 abstract:

### 05.10.2005 (Wednesday)

#### Quantum corrections to spinning strings

Triangular Seminar Sakura Schafer-Nameki (Hamburg)

 at: 16:30 QMWroom 410 abstract:

### 09.06.2005 (Thursday)

#### Noncentral extension of AdS superalgebra

Regular Seminar Jeong-Hyuck Park (IHES-Paris)

 at: 16:00 ICroom H503 abstract: Four dimensional N=4 super Yang-Mills theory contains a bigger superalgebra than AdS or superconformal algebra, su(2,2/4). It corresponds to a noncentral extension of the latter. The talk is for both physicsts and mathematicans interested in a novel way of obtaining noncentral extensions of Lie algebras.

### 19.05.2005 (Thursday)

#### Causality and locality in string and field theory

Regular Seminar Chong-Sun Chu (Durham)

 at: 14:00 QMWroom 112 abstract:

### 10.11.2004 (Wednesday)

#### GUT spectrum from Heterotic Compactification

Regular Seminar Yang-Hui He (University of Pennsylvania)

 at: 13:15 KCLroom 423 abstract:

### 25.10.2004 (Monday)

#### Correlation functions from spin chains with impurities

Triangular Seminar Olalla Castro-Alvaredo (Ecole Normale Superieure de Lyon)

 at: 15:00 City U.room Geary Room CM524 abstract: In this talk I will present a short review on the algebraic Bethe ansatz technique and on the recently found solution of the so-called inverse problem. I will show how this solution provides a means for the explicit and exact computation of correlation functions in spin chains and summarize some of the many results obtained in this direction by members of the theory group at the ENS-Lyon in the last years. Finally I will present some work still in progress which intends the generalization of these techniques to the case of spin chains in the presence of impurities.

### 21.10.2004 (Thursday)

#### Symmetry and supersymmetry in M-theory backgrounds

Regular Seminar Jose' Figueroa-O' Farrill (Edinburgh)

 at: 14:00 QMWroom 112 abstract: