Found at least 20 result(s)
Regular Seminar JeongHyuck Park (Sogang U.)
at: 14:00 room lecture theatre  abstract: How many H2O molecules are needed to form water? While the precise answer is not known, it is clear that the answer should be a finite number rather than infinity. We revisit with care the ideal Bose gas confined in a cubic box which is discussed in most statistical physics textbooks. We show that the isobar of the ideal gas zigzags on the temperaturevolume plane featuring a `boilinglike' discrete phase transition, provided the number of particles is equal to or greater than a particular value: 7616. This demonstrates for the first time how a finite system can feature a mathematical singularity and realize the notion of `Emergence', without resorting to the thermodynamic limit. ref: arXiv:1310.5580 
Regular Seminar Guy GurAri (Weizmann Institute)
at: 13:15 room S1.04  abstract: ChernSimons theories coupled to vector matter exhibit interesting phenomena. In the planar limit, these theories are conjectured to be holographically dual to generalized theories of gravity, involving highspin fields. This is a weakweak holographic duality that is in some aspects very simple, and may serve as a toy model for deepening our understanding of both holography and string theory. On the CFT side, exact calculations performed in the planar limit, along with constraints imposed by a ‘slightlybroken’ highspin symmetry, have led to many exact results. These have uncovered the details of a 3D bosonization duality, relating theories with bosonic matter to theories with fermionic matter. I will present dynamical evidence for this duality. 
Regular Seminar JeongHyuck Park (Sogang University Seoul and DAMTP Cambridge)
at: 13:15 room S4.23  abstract: To the full order in fermions, we construct D = 10 type II supersymmetric double field theory. We spell the precise N = 2 supersymmetry transformation rules as for 32 supercharges. In terms of a stringy differential geometry beyond Riemann, the constructed action unifies type IIA and IIB supergravities in a manifestly covariant manner with respect to O(10, 10) Tduality and a ‘pair’ of local Lorentz groups, or Spin(1, 9) × Spin(9, 1), besides the usual general covariance of supergravities or the generalized diffeomorphism. The distinction of IIA and IIB may arise after a diagonal gauge fixing of the Lorentz groups. They are identified as two different types of ‘solutions’ rather than two different theories. References: arXiv:1210.5078 (N=2) arXiv:1206.3478 (bosonic N=2) arXiv:1112.0069 (N=1) 
Regular Seminar Keiichi Maeda (Waseda)
at: 14:00 room H503  abstract: An exact solution representing black holes in an expanding universe is found. The black holes are maximally charged and the universe is expanding with arbitrary equation of state. It is an exact solution of the EinsteinscalarMaxwell system, in which we have two Maxwelltype U(1) fields coupled to the scalar field. The potential of the scalar field is an exponential. The solution depends on two parameters, the charge Q and one parameter (the ratio of the energy density of U(1) fields to that of the scalar field). We find a regular horizon, which is static because of the balance on the horizon between gravitational attractive force and U(1) repulsive force acting on the scalar field. We also calculate the black hole temperature. For the case without a potential, we can derive such a solution from a timedependent intersecting Mbrane solution in eleven dimensions by the dimensional reduction. 
Regular Seminar YangHui He (City University)
at: 13:00 room H341  abstract: We establish a correspondence between generalized quiver gauge theories in fourdimensions and congruence subgroups of the modular group, hinging upon the trivalent graphs which arise in both. The gauge theories and the graphs are enumerated and their numbers are compared. The correspondence is particularly striking for genus zero torsionfree congruence subgroups which are crucial to Moonshine. We analyze in detail the case of index 24, where modular elliptic K3 surfaces emerge: here, the elliptic jinvariants can be recast as dessins d'enfant which dictate the SeibergWitten curves. 
Regular Seminar ChongSun Chu (Durham)
at: 14:00 room H503  abstract:

Regular Seminar Jose FigueroaO'Farrill (Edinburgh)
at: 13:30 room H503  abstract: We've known since childhood that symmetry can be a very powerful tool in solving partial differential equations. With a little symmetry, one can reduce the number of independent variables, whereas with some more symmetry one can usually separate variables and reduce the problem to solving ordinary differential equations. Given enough symmetry, though, partial differential equations become algebraic. A large body of current research in our field requires finding solutions to the (super)gravity field equations and in this talk I will motivate the search for homogeneous supergravity backgrounds and mention some recent results in this area. 
Regular Seminar Sakura SchaferNameki (King's)
at: 14:00 room 602  abstract: String theory phenomenology generically suffers from either too much flexibility (and lack of predictability) or from the a high specialization to case by case studies. I will discuss how Ftheory GUT model building manages to get around these pitfall, in particular, I will explain, how to systematically include global string consistency conditions, which are independent of the specific compactification, and which come with the benefit of highly constraining the class of GUT models that can arise from Ftheory. 
Exceptional Seminar Sakura SchaferNameki (King's)
at: 16:00 room SB7.06  abstract: I will give an overview of recent developments in Ftheory GUT model building. First I will discuss the basic ideas of Ftheory model building, exemplifying this by the construction of supersymmetric SU(5) GUTs. Then I will outline how global string theoretic consistency requirements impact the SUSY phenomenology. The main focus of this talk will be on the phenomenological implications of these models. 
Regular Seminar Olof OhlssonSax (Uppsala)
at: 16:00 room CG05  abstract: The ABJM model is a superconformal ChernSimons theory with N = 6 supersymmetry which is believed to be integrable in the planar limit. However, there is a coupling dependent function that appears in the magnon dispersion relation and the asymptotic Bethe ansatz that is only known to leading order at strong and weak coupling. We compute this function to four loops in perturbation theory by an explicit Feynman diagram calculation for both the ABJM model and the ABJ extension. We then compute the fourloop wrapping correction for a scalar operator in the 20 of SU(4) and find that it agrees with a recent prediction from the ABJM Ysystem of Gromov, Kazakov and Vieira. We also propose a limit of the ABJ model that might be perturbatively integrable at all loop orders but has a short range Hamiltonian. 
Regular Seminar YangHui He (Oxford University)
at: 13:30 room Oakden  abstract: We present some new perspectives on N=1 gauge theories, especially SQCD, DBrane Quiver Theories and the MSSM, from the standpoint of recent advances in computational and algorithmic algebraic geometry and commutative algebra. We introduce the plethystic program which systematically count gauge invariants and encodes certain hidden symmetries. Moreover, we discuss special structures of the vacuum moduli space, such as that of SQCD being CalabiYau. 
Regular Seminar AmirKian KashaniPoor (ENS, Paris)
at: 14:00 room E303 Queens Building  abstract: In this talk, I will discuss work in progress with Bertrand Eynard, in which we derive the BKMP remodelling the Bmodel conjecture, in the large radius limit. This is the claim that GromovWitten invariants of any toric CalabiYau 3fold coincide with the spectral invariants of the mirror curve. Our method consists in explicitly constructing a matrix model which reproduces the topological string partition function obtained via the vertex formalism, and then demonstrating that the spectral curve of this matrix model coincides with the mirror geometry. 
Regular Seminar Ronald ReidEdwards (City University London)
at: 15:00 room Ronald ReidEdwards  abstract: In this seminar, I will give an introduction to a series of ideas which suggest that many aspects of quantum fied theories, including the celebrated N=4 super YangMills, may be most simply understood in terms of a dual theory in twistor space. No previous knowledge of string theory or twistor theory will be assumed. 
Regular Seminar Robert de MelloKoch (University of Witwatersrand)
at: 13:45 room 410A  abstract:

Regular Seminar Liora MalkiEpshtein (University College London)
at: 15:00 room C343  abstract: When a saltstratified fluid is cooled from the side, a twodimensional convection pattern of cells is formed along the vertical sidewall and develops into horizontal intrusions which grow away from the wall. Such conditions exist in the oceans along melting icebergs, and the growth of these intrusions prevents meltwater from rising to the surface. As the intrusions grow, a series of layers is created in the salt water, with stepped temperature and salinity profiles. In this talk, I will describe an experimental and theoretical study carried out while at the ITG in Cambridge on the formation and growth of these doublediffusive intrusions. Observations were made of growth rates of the intrusions, of internal velocities, and of temperature and salinity distributions. The rate of growth of the intrusions was found, surprisingly, to depend on the length of the experimental tank, with the endwall playing a role in their evolution right from the beginning of the experiment (MalkiEpshtein, Phillips and Huppert, JFM 2004). Internal waves are visualised using particle tracing methods and are shown to propagate throughout the experimental tank, maintaining hydrostatic equilibrium and having a strong role in setting up the layers. Future application of the results of this study to the large scale could have significant implications for the modelling of oceanic doublediffusive processes, which are believed to drive large vertical and lateral fluxes of heat and salt. 
Journal Club Ron ReidEdwards (Queen Mary)
at: 15:00 room 609  abstract: This is the first lecture of a short course on nongeometric backgrounds. For more information on the course and the schedule, please visit http://www.strings.ph.qmw.ac.uk/index.htm and follow the link to the Graduate Program in String/Field Theory. 
Regular Seminar EvaMaria Graefe (Technische Universitaet Kaiserslautern)
at: 15:00 room C343  abstract: We study an Nparticle, twomode BoseHubbard system, modelling a BoseEinstein condensate in a doublewell potential. By introducing effective complex energies to the modes we describe a coupling to a continuum. The eigenvalues of the resulting nonHermitian matrix model are in general complex where the imaginary parts (resonance widths) describe the decay rate into the continuum. In dependence on the parameters the spectrum shows an intricate structure of exceptional points, at which two or more eigenvalues as well as the corresponding eigenstates are degenerate. In the present talk the effect of the interplay between the particle interaction and the nonHermiticity on the spectrum is analysed, drawing special attention to the occurrence and unfolding of exceptional points. Some peculiarities are clarified using perturbational methods. 
Regular Seminar Adel AbulMagd (Sinai University)
at: 11:00 room M128  abstract: In analogy to Beck and Cohen's superstatistics (1), we connect the canonical Gaussian ensembles of the randommatrix 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 regularchaotic 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 inversechisquare distribution. The experimental distribution nearestneighbor 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. AbulMagd, Phys.Rev. E 71, 066207 (2005). (3) A.Y. AbulMagd, B. Dietz, T. Friedrich, and A. Richter, Phys. R 
Regular Seminar YangHui He (Oxford University)
at: 14:00 room Huxley 503  abstract: We point out a special corner in the space of CalabiYau compactifications where standardlike models tend to emerge. We show how these scenarios are interrelated 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. 