Swansea Theory Seminars 2008-2009

October 2008		November 2008		December 2008
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January 2009		February 2009		March 2009
Mo Tu We Th Fr Sa Su 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31		Mo Tu We Th Fr Sa Su 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28		Mo Tu We Th Fr Sa Su 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
April 2009		May 2009		June 2009
Mo Tu We Th Fr Sa Su 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30		Mo Tu We Th Fr Sa Su 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31		Mo Tu We Th Fr Sa Su 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

October

Wednesday, Oct. 8, 2008
Room 516, 2pm
Liuba Mazzanti (Ecole Polytechnique)
Gluon plasma thermodynamics from 5d holography

Abstract:

Thermodynamics of the gluon plasma are well described holographically by the 5d dilaton-gravity model we propose. The asymptotics of the dilaton potential is determined at zero temperature by requiring asymptotic freedom and confinement. The glueball spectrum is consistent with lattice simulations. I'll show that at finite temperature this model exhibits a first order Hawking-Page phase transition. I will describe the deconfined black hole solution which dominates at high temeratures. Furthermore, thermodynamics quantities are found to be in good qualitative agreement with lattice data, displaying the expected behavior for the gluon plasma.

Friday, Oct. 10, 2008
Room 516, 2pm
One A4 slide session


Abstract:

All members of the department introduce themselves using a single A4 transparency.

Friday, Oct. 17, 2008
Room 516, 2pm
Daniel Elander (Swansea)
Phase Structure of Beta-deformed N=4 SYM

Abstract:

The beta-deformation of N=4 SYM preserves conformal symmetry, but breaks the amount of supersymmetry to N=1. On S^3, there are critical values for the chemical potentials associated with the U(1)^3 R-symmetry, above which classically the theory becomes unstable. Calculating the one-loop effective potential, we will describe how this result is modified by quantum and thermal effects, leading to the existence of metastable states for near critical chemical potentials. We will also describe how to obtain the gravity dual of the theory at finite temperature and with chemical potentials, by performing a TsT-transformation on a solution describing an AdS_5 black hole spinning in S^5. A probe-brane calculation reveals qualitative agreement with the weak coupling results.

Wednesday, Oct. 29, 2008
Room 516, 2pm
Roberto Auzzi (Swansea)
Non-Abelian k-Vortices in N=1^* theory and their Gravity Duals

Abstract:

We study magnetic flux tubes in the Higgs vacuum of the N=1^* mass deformation of SU(N_c), N=4 SYM and its large N_c string dual, the Polchinski-Strassler geometry. Choosing equal masses for the three adjoint chiral multiplets, for all N_c we identify a "colour-flavour locked" symmetry, SO(3)_{C+F} which leaves the Higgs vacuum invariant. At weak coupling, we find explicit non-Abelian k-vortex solutions carrying a Z_{N_c}-valued magnetic flux, with winding, 0 < k < N_c. These k-strings spontaneously break SO(3)_{C+F} to U(1)_{C+F} resulting in an S^2 moduli space of solutions. The world-sheet sigma model is a nonsupersymmetric CP^1 model with a theta angle \theta_{1+1} = k(N_c-k)\theta_{3+1} where \theta_{3+1} is the Yang-Mills vacuum angle. We find numerically that k-vortex tensions follow the Casimir scaling law T_k \propto k (N_c-k) for large N_c. In the large N_c IIB string dual, the SO(3)_{C+F} symmetry is manifest in the geometry interpolating between AdS_5 x S^5 and the interior metric due to a single D5-brane carrying D3-brane charge. We identify candidate k-vortices as expanded probe D3-branes formed from a collection of k D-strings. The resulting k-vortex tension exhibits precise Casimir scaling, and the effective world-sheet theta angle matches the semiclassical result. S-duality maps the Higgs to the confining phase so that confining string tensions at strong 't Hooft strong coupling also exhibit Casimir scaling in N=1^* theory in the large N_c limit.

November

Thursday, Nov. 6, 2008
Common Room, 1:30pm
Joyce Myers (Swansea)
Phase diagrams of SU(N) gauge theories with fermions in various representations

Abstract:

We minimize the one-loop effective potential for SU(N) gauge theories with fermions in various representations and compare with lattice simulations of a related model. We consider fundamental (F), adjoint (Adj), symmetric (S), and antisymmetric (AS) representation fermions with finite mass m. We calculate the phase diagram as a function of the length of the compact time dimension beta and the fermion mass for various N and Nf. We also consider the quantum effects of periodic boundary conditions [PBC(+)] on fermions as well as the finite temperature effects of antiperiodic boundary conditions [ABC(-)].

Monday, Nov. 10, 2008
Common Room, 2:00pm
Alexei Bazavov (University of Arizona)
Upcoming Large-scale Simulations with Highly Improved Staggered Quarks in Lattice QCD

Abstract:

Lattice QCD allows to study many non-perturbative properties of strongly interacting matter from first principles. Physical results are recovered in the continuum limit (the lattice spacing a approaching zero). Recent progress in lattice simulations is largely due to the use of improved actions that suppress discretization errors and allow to perform calculations closer to the continuum limit. In this talk I report on employing the Highly Improved Staggered Quarks (HISQ) action in large-scale simulations with dynamical fermions. The HISQ action is an O(a^2) Symanzik-improved action with further suppressed taste symmetry violations. The improvement in the taste symmetry is achieved by introducing the Fat7 smearing of the original gauge links and reunitarization followed by the Asq-type smearing. I present a study of the HISQ action on two 2+1+1 flavor ensembles with the lattice spacing roughly equivalent to the MILC asqtad a=0.125 and 0.09 fm ensembles. Following the success of the asqtad program, employing HISQ is the next step towards bringing Lattice QCD calculations to the level of high accuracy.

Wednesday, Nov. 12, 2008
Room 516, 2pm
Antonella De Santo (Royal Holloway)
Hunting for SUSY at ATLAS

Abstract:

The start-up of the Large Hadron Collider represents an epochal event in the history of Particle Physics, expected to deliver step-change advancements in our understanding of the sub-nuclear world and of our Universe. The search for supersymmetry, one of the most accredited and exciting extensions to the Standard Model, is one of the main physics objectives at ATLAS. I will discuss the main supersymmetric signatures at ATLAS and illustrate the experiment's search strategies and its physics potential to discover SUSY.

Friday, Nov. 14, 2008
Room 516, 2pm
Jefferson Ridgway (Swansea)
k-string widths in confining theories

Abstract:

We look at the quantum broadening (width) of k-strings. We generalise an old result by Luscher, Munster and Weisz to the case of a k-string, by using the gauge/gravity correspondence. When the fundamental QCD string is replaced by a bound state of k strings, the bound state is better described as a wrapped D-brane. We discuss the width of the k-string in Hardwall AdS and N=1 SYM gravity duals, by using a D-brane probe, and find a universal result.

Friday, Nov. 21, 2008
Room 516, 2pm
Antonio Amariti (INFN, Sezione di Milano-Bicocca)
Aspects of metastable vacua and R symmetry breaking

Abstract:

I review the basic properties of ISS model, focusing of the analysis of stability of the vacuum and on its embedding in model building. I then extend ISS to models with adjoint matter and to quiver gauge theories. I discuss various problems, like R-symmetry breaking, gauging of flavour symmetries and geometrical origin of the susy breaking scales. Finally I conculde with some new result on spontaneous R symmetry breaking from two loop.

Friday, Nov. 28, 2008
Room 516, 2pm
Andreas Athenodorou (Oxford)
Closed SU(N) flux tubes as Nambu-Goto strings in D=2+1

Abstract:

We calculate the excitation spectrum of closed k=1, 2 flux tubes in 2+1 dimensional SU(N) gauge theories. We do so using lattice techniques. We obtain unambiguous evidence that the closed fundamental strings are in the universality class of the Nambu-Goto free bosonic string. Our results demonstrate that the low-lying spectrum of the k=2 string falls into sectors that belong to nearly pure antisymmetric and symmetric representations. We also observe that the lightest states in each k=2 irreducible representation are consistent with what one would expect from an effective string theory that belongs to the same bosonic universality class as Nambu-Goto. In addition we observe unbound fundamental w=2 states.

December

Wednesday, Dec. 3, 2008
Room 516, 4:30pm
Paul Chesler (U. Washington)
Creating anisotropic plasma and dual black holes

Abstract:

Hydrodynamic simulations of heavy ion collisions at RHIC have demonstrated that the quark-gluon plasma produced is strongly coupled. The applicability of hydrodynamics suggests a very fast isotropization time of roughly 1 fm/c. Estimates of the isotropization time based on perturbative techniques are too large so it is desirable to have an estimate in a strongly coupled setting. Gauge/gravity duality provides a setting to study dynamics of strongly coupled supersymmetic Yang-Mills plasma. Using gauge/gravity duality, I will describe a toy model where an translationally invariant anisotropic plasma is created. This toy model will allow for the study of relaxation times of non-hydrodynamic degrees of freedom in a strongly coupled far from equilibrium setting.

Friday, Dec. 5, 2008
Room 516, 2pm
Benjamin Basso (Universite Paris XI, ORSAY)
CUSP ANOMALOUS DIMENSION IN N=4 SUPER-YANG-MILLS THEORY AT STRONG COUPLING

Abstract:

The cusp anomalous dimension is an important observable in four dimensional gauge theories, ranging from QCD to maximally supersymmetric N=4 Yang-Mills theory (SYM), as it governs the scaling behavior of various gauge invariant quantities a priori unrelated. The cusp anomalous dimension is a function of the gauge coupling only and its weak coupling expansion is known up to four loops in planar N=4 SYM. At strong coupling, assuming the AdS/CFT correspondence, the first few terms of its strong coupling expansion have been derived from the semiclassical expansion of the energy of a folded string rotating in the AdS_3 part of the target space. Recently, an integral equation was proposed (BES equation) that is believed to govern the cusp anomalous dimension at any value of the coupling constant. This equation, based on the conjectured all-loop integrability of the planar gauge theory, succeeded in reproducing the four-loop result at weak coupling. We shall present the strong coupling expansion of the cusp anomalous dimension obtained from this equation and discuss the agreement with the string theory prediction.

Wednesday, Dec. 10, 2008
Room 516, 2:00pm
Arnab Kundu (USC)
"External Fields and the Dynamics of Flavours in Holographic Duals of Large N Gauge Theories."

Abstract:

Using ten dimensional dual string backgrounds, we study aspects of the physics of finite temperature large N SU(N) gauge theories, focusing on the dynamics of fundamental quarks in the presence of an external field. In a background magnetic field we find the quark dynamics lead to spontaneous chiral symmetry breaking and establish a non-trivial phase structure in the temperature-magnetic field plane. We work with two particular dual string backgrounds coming from type IIB and type IIA supergravity and demonstrate how the phase structure emerges. We also comment on the dynamics of flavours in an external electric field.

Friday, Dec. 12, 2008
Room 516, 2pm
James Ettle (Swansea)
A MHV Lagrangian for QCD

Abstract:

I review the construction of a MHV lagrangian for pure Yang--Mills by canonical transformation of the field variables. This results in a lagrangian with infinite series of interaction terms, each a Parke--Taylor MHV amplitude. I then explain how this is extended to obtain a MHV lagrangian for a simple massless, single-flavour QCD theory with quarks in the fundamental representation; and consider briefly how mass may be added to the construction.

Monday, Dec. 15, 2008
Room 516, 2pm
Jerome Gaillard (Swansea)
Geometry and flavoring gauge-string dualities

Abstract:

Making use of generalized calibrated geometry and G-structures we put the problem of finding string-duals with smeared backreacting flavor branes in a more mathematical setting. This more formal treatment of the problem allows us to easily smear branes without good coordinate representations, establish constraints on the smearing form. We then apply this method to the problem of flavoring a supergravity-dual to a d=3 N=2 super Yang-Mills-like theory. We find new solutions to both the flavored and unflavored systems. Interpretating these turns out to be difficult.

January

Wednesday, Jan. 21, 2009
Room 516, 2pm
Oliver J Rosten (Dublin Institute for Advanced Studies)
Triviality from the Exact Renormalization Group

Abstract:

After reviewing Wilson's picture of renormalization, and the associated Exact Renormalization Group, I will show that no (physically acceptable) non-trivial fixed points exist for scalar field theory in D>=4. Consequently, an asymptotic safety scenario is ruled out, and the triviality of the theory is confirmed.

February

Wednesday, Feb. 4, 2009
Room 516, 2pm
David Lin (Taipei)
Learning to walk step by step on the lattice

Abstract:

We propose a new scheme for calculating the coupling constant using the step-scaling method. The scheme is defined via the Wilson loop in finite volume and can be used to look for candidate theories for the Walking Technicolour scenario in electroweak symmetry breaking. We have performed a feasibility numerical study of this method in quenched QCD.

Friday, Feb. 13, 2009
Room 516, 2pm
Joost Slingerland (DIAS Dublin)
TBA

Abstract:

TBA

Wednesday, Feb. 18, 2009
Room 413, 2pm
Gert Aarts (Swansea)
QCD at finite chemical potential: stochastic quantization and complex Langevin dynamics

Abstract:

Friday, Feb. 20, 2009
Room 516, 2pm
Claudio Pica (Edinburgh University)
TBA

Abstract:

TBA

Monday, Feb. 23, 2009
Room 516, 2pm
Shailesh Chandrasekharan (Duke University)
World-Line Approach to Lattice Field Theories

Abstract:

TBA

Friday, Feb. 27, 2009
Room 516, 2pm
Alex Hamilton (University of Cape Town)
Fluctuations of Giant Gravitons in AdS_4 x CP^3 based on hep-th/0901.0009

Abstract:

The dynamics of branes has long played a major role in understanding the true microscopic degrees of freedom in string theory. In particular, giant gravitons, while protected by supersymmetry, can have a rich interaction structure with the open strings to which they couple. The spectrum of these open string fluctuations, and their interactions with the giants, thus play a key role in our understanding not only of the branes themselves, but also have led to dramatic insights into the AdS/CFT gauge/gravity duality. With the recent emergence of an M-theoretic version of the duality, these fluctuation degrees of freedom offer a unique window into the microscopic M-theory degrees of freedom, and the relatively mysterious interactions between M-branes. In this talk, I will begin the discussion of these fluctuations from both the gravity and gauge theory perspective, and outline the path we are taking towards such an understanding.

March

April

May

June