Conveners
Theoretical Developments
- Yannick Meurice
Theoretical Developments
- Anthony Kennedy
Theoretical Developments
- Tatsuhiro Misumi
Theoretical Developments
- Richard Brower
Theoretical Developments
- Masanori Okawa
Theoretical Developments
- Goro Ishiki
Prof.
Anthony Kennedy
(University of Edinburgh)
15/07/2015, 14:00
Theoretical Developments
Talk
Symanzik showed that quantum field theory can be formulated on a space with boundaries by including suitable surface interactions in the action to implement boundary conditions. We show that to all orders in perturbation theory all the divergences induced by these surface interactions can be absorbed by a renormalization of their coefficients.
Mr
Aleksandr Ivanov
(Faculty of Physics M.V.Lomonosov Moscow State University)
15/07/2015, 14:20
Theoretical Developments
Talk
The small coupling expansions in the lattice field theory are asymptotic
and do not converge. It was shown in previous studies, that an appropriate regularization of the integrals or shifting of the initial approximation allows one to construct convergent series.
In this work we study the convergent series in application to the lattice $\phi^4$-model
and compare the observables calculated...
Robert Lohmayer
(University of Regensburg)
15/07/2015, 14:40
Theoretical Developments
Talk
We study pure SU(N) lattice gauge theory with a plaquette weight factor given by an inverse determinant which can be written as an integral over auxiliary bosonic fields (modifying a proposal of Budczies and Zirnbauer). We derive conditions for the existence of a continuum limit and its equivalence to Yang-Mills theory. Furthermore, we perturbatively compute the relation between the coupling...
Mr
Ryo Yamamura
(Osaka U.)
15/07/2015, 15:00
Theoretical Developments
Talk
Recently, Kaplan proposed an interesting extension of QCD : XQCD (=extended QCD) with bosonic auxiliary fields. While its partition function is kept exactly the same as that of QCD, XQCD naturally contains properties of low-energy hadrons.
We apply this extension to the two-dimensional QCD in the large N_c limit ('t Hooft model). In this solvable model, it is possible to directly examine the...
Mr
Arthur Dromard
(Goethe University Frankfurt am Main)
15/07/2015, 15:20
Theoretical Developments
Talk
In lattice simulations at fine lattice spacings typical algorithms tend to freeze topologically. In such cases specific topological finite size effects have to be taken into account, to obtain physical results corresponding to infinite volume or unfixed topology. Moreover, in QCD simulations, where the volume is not that large, it is often also necessary to get rid of ordinary finite volume...
Dr
Akaki Rusetsky
(HISKP, University of Bonn)
15/07/2015, 15:40
Theoretical Developments
Talk
The spectrum of a bound state of three identical particles with a mass $m$ in a finite cubic box is studied within the effective field theory approach. It is shown that in the limit of a large two-body scattering length, the energy shift of a shallow bound state is given by
$\Delta E=c (\kappa^2/m) (\kappa L)^{-3/2}|A|^2 \exp(โ2\kappa L/\sqrt{3})$,
where $\kappa$ is the bound-state...
Mr
Boye Buyens
(Ghent University)
15/07/2015, 16:30
Theoretical Developments
Talk
We consider the matrix product state formalism for the simulation of Hamiltonian lattice gauge theories. To this end, we define matrix product states which are manifestly gauge invariant. As an application, we study 1+1 dimensional one flavor quantum electrodynamics, also known as the massive Schwinger model. First, we discuss our results on full quantum non-equilibrium dynamics induced by a...
Dr
Debasish Banerjee
(DESY Zeuthen)
15/07/2015, 16:50
Theoretical Developments
Talk
We set up a real-time path integral to study the evolution of quantum systems driven in real-time completely through the coupling of the system with the environment. This can also be interpreted as measurements being performed on the system. For a spin-1/2 system, in particular, when the measurement results are averaged over, the resulting sign problem completely disappears, and the system can...
Mr
Yuya Tanizaki
(University of Tokyo)
15/07/2015, 17:10
Theoretical Developments
Talk
Lefschetz-thimble method is a recently developing tool for solving the sign problem. We showed that the sign problem appearing in the mean-field approximation can be completely solved by applying this technique. The manifest reality of the physical observables is shown to be ensured in spite of the complexification of the field variables. The result is demonstrated through the heavy-quark...
Dr
Hana Saito
(DESY)
15/07/2015, 17:30
Theoretical Developments
Talk
The Schwinger model, or 1+1 dimensional QED, offers an interesting object of study, both at zero and non-zero temperature, because of its similarities to QCD. In this talk we present the first full calculation of the temperature dependent chiral condensate of this model in the continuum limit using Matrix Product States (MPS). MPS methods, in general tensor networks, constitute a very...
Mr
Hikaru Kawauchi
(Kanazawa University)
15/07/2015, 17:50
Theoretical Developments
Talk
We apply the tensor renormalization group (TRG) method to the lattice CP(N-1) model in two dimensions. A tensor network representation of this model is derived for arbitrary N. For N=2, we compute the average energy by using the higher-order TRG. We compare it with the result of the O(3) nonlinear sigma model in two dimensions which is analyzed by the same method. Finally, we discuss the...
Prof.
Yannick Meurice
(University of Iowa)
15/07/2015, 18:10
Theoretical Developments
Talk
We discuss the Tensor Renormalization Group (TRG) method for various
spin and gauge lattice models in 1+1 dimensions with emphasis
on near gapless/conformal situations. We present recent progress on optimized truncation
methods. We describe the entanglement entropy in the superfluid phase of the
O(2) model with a chemical potential.
Mr
Christian Zielinski
(Nanyang Technological University)
16/07/2015, 10:40
Theoretical Developments
Talk
The 4 flavors of the usual staggered fermion give rise to 16 pions (pseudoscalar mesons). We study the effect on the pion spectrum of turning on the 2-flavor staggered Wilson term in the staggered fermion action. 8 of the pions become heavy while 8 remain light. 6 of the light pions are identified as two copies of the 2-flavor pion triplet. They have the same light quark content but different...
James Osborn
(ANL)
16/07/2015, 11:00
Theoretical Developments
Talk
We present a new discretization of the lattice Dirac operator that preserves chiral symmetry while suppressing the effects of doubler states. The new operator is constructed from the naive Dirac operator by filtering out doubler states while preserving one physical quark state. In the simplest version the filtering is only approximate and the filter would require fine tuning to produce a...
Dr
Agostino Patella
(CERN and Plymouth University)
16/07/2015, 11:20
Theoretical Developments
Talk
In order to calculate QED corrections to hadronic quantities by means of lattice simulations, a coherent description of electrically-charged states in finite volume is needed. In the usual periodic setup, Gauss' law and large gauge transformations forbid the propagation of electrically-charged states. A possible solution to this problem, which does not violate the axioms of local quantum field...
Dr
Nazario Tantalo
(Rome University and INFN "Tor Vergata")
16/07/2015, 11:40
Theoretical Developments
Talk
In order to calculate QED corrections to hadronic quantities by means of lattice simulations, a coherent description of electrically-charged states in finite volume is needed. In the usual periodic setup, Gauss' law and large gauge transformations forbid the propagation of electrically-charged states. A possible solution to this problem, which does not violate the axioms of local quantum field...
Dr
Alberto Ramos
(CERN)
17/07/2015, 14:00
Theoretical Developments
Talk
We will use the idea of twisted reduction and volume independence to numerically investigate the large N limit of Yang-Mills theories by reducing two of the directions to a single point. We will show that this framework might be convenient to analyze some properties of these theories.
Prof.
Masanori Okawa
(Hiroshima University)
17/07/2015, 14:20
Theoretical Developments
Talk
We propose a new method to calculate meson propagators in the large N limit from twisted space-time reduced model. Preliminary results of meson spectra and decay constants are presented.
Dr
Alessandro Amato
(University of Helsinki)
17/07/2015, 14:40
Theoretical Developments
Talk
It is well known that the topology of gauge configurations generated
in a Markov Monte-Carlo chain freezes as the continuum limit
is approached. The corresponding autocorrelation time increases
exponentially with the inverse lattice spacing, affecting the ergodicity
of the simulation. In SU(N) gauge theories for large N this problem sets
in at much coarser lattice spacings than for N=3....
Dr
Pavel Buividovich
(Regensburg University)
17/07/2015, 15:00
Theoretical Developments
Talk
I present a general framework for constructing Diagrammatic Monte-Carlo algorithms for large-N quantum field theories, which is based on the stochastic solution of the full untruncated hierarchy of Schwinger-Dyson equations and is an extension of the approach proposed in arXiv:1104.3459, arXiv:1009.4033. The algorithms are capable of constructing both weak- or strong-coupling expansions which...
Mr
Semen Valgushev
(University of Regensburg)
17/07/2015, 15:20
Theoretical Developments
Talk
It is known that the 1/N expansion in the Gross-Witten U(N) matrix model is divergent and leading divergence in the weak coupling regime is governed by instanton which is associated with eigenvalue tunneling. However, it was not known what triggers divergences in the strong coupling phase where instantons disappear. To address this problem, we numerically study structure of saddle points in...
Prof.
Goro Ishiki
(University of Tsukuba)
17/07/2015, 15:40
Theoretical Developments
Talk
Some matrix models have been proposed as a non-perturbaive formulation of string theories. In the matrix model formulation of string theories, configurations of strings or D-branes are described by a set of Hermitian matrices. Here, we propose a new class of observables in matrix models, which are made of the Hermitian matrices and encode geometric information of the strings or D-branes. By...
Prof.
Richard Brower
(Boston University)
17/07/2015, 16:30
Theoretical Developments
Talk
Viable non-perturbative methods for quantum field theories on curved
manifold are difficult. By adapting features from both the
traditional finite element methods (FEM) and simplicial Regge
calculus we are developing a Quantum Finite Element Method(QFEM).
To test the QFEM approach, we study the $\lambda \phi^4$ on the
simplicial lattice for the Riemann Sphere. To reach the
...
Dr
George Fleming
(Yale University)
17/07/2015, 16:50
Theoretical Developments
Talk
We demonstrate the quantum finite element method (QFEM) by computing known properties of the 2-D Wilson-Fisher fixed point using scalar field theory on 2-sphere.
Mr
Andrew Gasbarro
(Yale University)
17/07/2015, 17:10
Theoretical Developments
Talk
Recent efforts have been made to study conformal field theories in radial quantization on the lattice. The lattice necessarily breaks spherical symmetry down to icosahedral symmetry, so efforts must be made to restore spherical symmetry โ even at the classical level โ by clever construction of the action. Linear finite elements have been shown to improve the spectrum of the Laplacian. In...
Prof.
Sinya Aoki
(Kyoto University)
17/07/2015, 17:30
Theoretical Developments
Talk
We propose a method, which encodes the information of a $d$ dimensional quantum field theory into a $d+1$ dimensional gravity in the $1/N$ expansion. We first construct a $d+1$ dimensional field theory from the $d$ dimensional one via the gradient flow equation, whose flow time $t$ represents the energy scale of the system such that $tยฅrightarrow 0$ corresponds to the ultra-violet (UV)...
Prof.
Noboru KAWAMOTO
(Hokkaido University)
17/07/2015, 17:50
Theoretical Developments
Talk
Recently we have proposed a lattice SUSY formulation which we may call super doubler approach, where chiral fermion species doublers are identified as super partners of extended supersymmetry. We claim that the super symmetry is exactly kept on the lattice. However the formulation is nonlocal and breaks lattice translational invariance. We argue that these features cause no fundamental...
Mr
Norihiko Kamata
(Tohoku Univ)
18/07/2015, 09:00
Theoretical Developments
Talk
Recently, the Yang-Mills gradient flow method has continued to develop remarkably. The most successful application is demonstrated in an accurate determination of a reference scale. However, there is still room for improvement with respect to the lattice gradient flow, where some lattice artifacts are found to be non-negligible. Following a recent paper by Fodor et al. (arXiv:1406.0827), we...
Mr
Francesco Capponi
(Plymouth University)
18/07/2015, 09:20
Theoretical Developments
Talk
We implement two different strategies for the non perturbative determination of the renormalized energy momentum tensor in SU(3) Yang-Mills on the lattice.
Both strategies employ observables built with gauge fields that evolve according to the Yang Mills gradient flow.
In the first case, we use observables computed along the flow in order to define suitable lattice Ward Identities from which...
Dr
Etsuko Itou
(KEK)
18/07/2015, 09:40
Theoretical Developments
Talk
Recently, we proposed a novel method to define and calculate the energy-momentum tensor (EMT) in lattice gauge theory on the basis of the Yang-Mills gradient flow.
In this talk, we show the bulk thermodynamic quantities in lattice gauge theory using this method for (2+1)-flavor QCD.
The entropy density of (2+1)-flavor QCD at fixed temperature are calculated.
We also show the flow time...
Prof.
Hiroshi Suzuki
(Kyushu University)
18/07/2015, 10:00
Theoretical Developments
Talk
We develop a background field method and associated gauge fixing prescription in gradient flow equations. By using this formulation, we carry out non-diagramatic one-loop computations of the small flow time expansion of gauge invariant composite operators, aiming for the application to the energy-momentum tensor and the flavor-singlet axial-vector current on the lattice.
Dr
Kengo Kikuchi
(Yukawa Institute for Theoretical Physics, Kyoto University)
18/07/2015, 10:20
Theoretical Developments
Talk
We generalize the gradient flow equation for field theories with nonlinearly realized symmetry. We apply the method to two theories, the super Yang-Mills theory in four dimensions and the O(N) nonlinear sigma model in two dimensions. Firstly, applying the formalism to super Yang-Mills theory, we construct the supersymmetric gradient flow equation. Furthermore, choosing an appropriate...
Ms
Susanne Ehret
(University of Edinburgh)
18/07/2015, 10:40
Theoretical Developments
Talk
A nonperturbative renormalization prescription for the energy-momentum tensor, based on space-time symmetries along the Wilson flow, has been proposed recently in the context of four-dimensional gauge theories. We extend this construction to the case of a scalar field theory, and investigate its numerical feasibility by studying Ward identities in 3-dimensional phi^4 theory.
In this talk, we...
