2013年度のセミナー

 Date/Place 18 Feb. (Tue.) 15:30～ / H711 Anna Hasenfratz (University of Colorado Boulder) Strongly coupled gauge theories in and out of the conformal window(slides) Asymptotically free gauge systems with many fermionic degrees of freedom can develop a conformal infrared fixed point. Near the conformal window these strongly coupled systems can have unusual properties, and might contain a light scalar, a composite candidate for the Higgs boson. Lattice studies are particularly suited to study these strongly coupled models, though methods developed for QCD studies are not always effective. In this talk I will give a brief overview of our understanding of these systems. I will concentrate on two rather different methods, the Dirac operator spectral density, and a variant of finite size scaling, to illustrate the unusual properties of these intriguing systems.

 Date/Place 10 Feb. (Mon.) 15:30～ / H711 Toshihiro Matsuo (Anan Kosen) Greybody Factor of Heavy Superstring(slides) It is well known that a heavy superstring has huge degeneracy and thus the entropy of the string is comparable to that of black holes. The heavy superstring also shows thermal radiation similar to black holes. We calculate emission rates of various bosonic/fermionic soft massless states of an open/closed superstring in the flat background by using the Green-Schwarz formalism. We find greybody factors for each process and argue their relation to the ones from black holes. The result consistently suggests to the new interpretation of the black hole/string correspondence principle proposed by Giveon-Kutasov.

 Date/Place 28 Jan. (Tue.) 16:30～ / H711 Kentaro Nagamine (Osaka Univ.) Cosmology and Structure Formation(slides) The remarkable progress of large-scale astronomical surveys in the last two decades have allowed us to constrain the current cosmological model to an unprecedented precision. At the same time, the field of computational cosmology has emerged, and evolved hand-in-hand with the observational cosmology. In this talk, I will review the history and current status of observational cosmology, and describe how supercomputers have helped to shape our current views of cosmological structure formation. The keyword in the frontier of structure formation study is the `Feedback'.

 Date/Place 21 Jan. (Tue.) 15:30～ / H711 Tetsuya Onogi (Osaka Univ.) Position space formulation for Dirac fermions on honeycomb lattice(slides) We study how to construct Dirac fermion defined on the honeycomb lattice in position space. Starting from the tight binding model, we show that the Hamiltonian describes lattice Dirac fermions for three flavors, two of which are massless. We show that there is an exact chiral symmetry at finite lattice spacing, which protects the masslessness of the Dirac fermion.

 Date/Place 14 Jan. (Tue.) 15:30～ / H711 Takao Suyama (Seoul National univ.) A Systematic Study on Matrix Models for Chern-Simons-matter Theories(slides) We investigate the planar solution of matrix models derived from various Chern-Simons-matter theories compatible with the planar limit. The saddle-point equations for most of such theories can be solved in a systematic way. A relation to Fuchsian systems play an important role in obtaining the planar resolvents. For those theories, the eigenvalue distribution is found to be confined in a bounded region even when the 't Hooft couplings become large. As a result, the vevs of Wilson loops are bounded in the large 't Hooft coupling limit. This implies that many of Chern-Simons-matter theories have quite different properties from ABJM theory. If the gauge group is of the form U(N_1)_{k_1} x U(N_2)_{k_2}, then the resolvents can be obtained in a more explicit form than in the general cases.

 Date/Place 7 Jan. (Tue.) 15:30～ / H711 Masahiro Takada (IPMU) The large-scale structure of the Universe: the current status and future prospects(slides) The large scale structure of the universe can be a powerful probe of our universe, including the nature of dark energy, modified gravity, inflation, neutrino mass etc. Weak lensing and galaxy clustering can both be used to study the large scale structure of the universe. I will review the strengths and weaknesses of these techniques, their current status and the planned projects for the future. In particular, I wold also like to introduce the Subaru Measurements of Images and Redshifts (SuMIRe project), which is the project being led by IPMU, aimed at achieving high-precision cosmology via accurate measurements of the large-scale structure probes.

 Date/Place 10 Dec. (Tue.) 15:30～ / H711 Takehiko Asaka (Niigata univ.) "Probing the origins of neutrino masses and baryon asymmetry of the universe"(slides) We consider the Standard Model extended by two quasi-degenerate right-handed neutrinos. In particular, we consider the case when they are lighter than charged kaon. This simple framework can account for the neutrino oscillations and the baryon asymmetry of the universe at the same time. In this talk we shall summarize the possible constraints on such right-handed neutrinos from direct search experiments and cosmology, and also discuss the strategy how to find and verify right-handed neutrinos by using the future experiments by using kaon.

 Date/Place 6 Dec. (Fri.) 16:30～ / H711 Masanori Okawa(Hiroshima Univ.) Twisted space-time reduction in large N QCD with adjoint Wilson fermions(slides) The twisted reduced model of large N QCD with two adjoint Wilson fermions is constructed applying the symmetric twist boundary conditions with flux k. This is the one-site model, whose large N limit (large volume limit) is expected to be conformal or nearly conformal. The string tension calculated at N=289 approaches zero as we decrease quark mass in the way consistent with the theory governed by an infrared fixed point. We also discuss the twisted reduced model with single adjoint Wilson fermion. The string tension remains finite as the quark mass decreases to zero, supporting that this is the confining theory.

 Date/Place 3 Dec. (Tue.) 15:30～ / H711 Ryuichiro Kitano(KEK, Sokendai) Quark Confinement via Magnetic Color-Flavor Locking(slides)

 Date/Place 26 Nov. (Tue.) 15:30～ / H711 Yuta Orikasa(Osaka univ.) Electroweak symmetry breaking in the flatland(slides) Bardeen has argued that once the classically conformal invariance and its minimal violation by quantum anomalies are imposed on the SM, it can be free from the quadratic divergences. The running coupling vanished near the Planck scale, which indicates a possible link between the physics in the electroweak and the Planck scale. Motivated by these two things, we investigate a possibility that the Higgs has a flat potential at Planck scale. We show that the flat potential scenario is realizable only when an inequality k<1 among the coefficients of the beta function is satisfied. We show several models satisfying the condition

 Date/Place 19 Nov. (Tue.) 15:30～ / H711 Takeshi Fukuyama (RCNP) Derivation of Generalized Thomas-Bargmann-Michel-Telegdi Equation for a Particle with Electric Dipole Moment (slides) Anomalous magnetic dipole moment and electric dipole moment (EDM) of elementary particles are smoking guns of the BSM physics. These are measured in storage ring, where particles obey the generalised Bergmenn-Michel-Telegdi (BMT) equation with EDM. In this talk the generalized equation is explicily calculated to include EDM. The result itself is not new but known as the conjecture from dual transformation between E and B. However, this is not so simple as you can guess from the Thomas g factor etc.

 Date/Place 12 Nov. (Tue.) 15:30～ / H711 Kenta Murase (Kyoto Univ.) Quantum 3D Tensionless String in Light-cone Gauge (slides) Tensionless p-branes have no Lorentz anomaly in any space-time dimensions and no anomaly of space-time conformal symmetry in two dimensions. We can check these facts by using a Hamiltonian BRST scheme. In 2010, L. Mezincescu and P. K. Townsend showed that a 3D tensile string in light-cone gauge has no Lorentz anomaly and found “anyons” in its spectrum. Recently we found that a quantum 3D tensionless closed string in light-cone gauge has no anomaly of space-time conformal symmetry. In this talk, I will introduce the properties of tensionless strings in general dimensions and talk about the quantization of a 3D tensionless closed string in light-cone gauge. (This talk is based on the work arXiv:1303.7202 )

 Date/Place 29 Oct. (Tue.) 15:30～ / H711 Yukinari Sumino (Tohoku Univ.) Understanding Heavy Quark-AntiQuark System by Perturbative QCD (slides) Around 1998, due to the discovery of renormalon cancellation, it became possible to describe the nature of a heavy quark-antiquark system (such as bottomonium) based on perturbative QCD, both qualitatively and quantitatively. Accordingly, interpretaions of the heavy quark mass and interquark force have been modified considerably. I overview what has been understood and theoretical progress since then. For instance, the renormalon dominance picture has been confirmed to be valid and predicts a Coulomb+linear shape of the interquark potential. We also review briefly applications such as high precision determinations of the b,c,t quark masses and alpha_s. 1, 2, 3, 4

 Date/Place 22 Oct. (Tue.) 15:30～ / H711 Takuya Kakuda (Osaka/Niigata Univ.) The vacuum stability in the standard model and New physics scale The LHC shows us the accuracy of the standard model prediction, it reveals that there is no new physics in a few TeV scale one after another. (We show the bounds on Universal Extra Dimension models as the example of the new physics.) Thus we return to the standard models and it's vacuum stability bound to find the hint of the new physics scale. We give the remark to the previous work which using effective potential to find the vacuum stability bound and show our preliminary result of the running of Higgs quartic interaction.

 Date/Place 15 Oct. (Tue.) 15:30～ / H711 Yoshinori Matsuo (KEK) A new look at instantons and large-N limit (slides) We analyze instantons in the very strongly coupled large-N limit (N->Infinity with g^2 fixed) of large-N gauge theories, where the effect of the instantons remains finite. By using the exact partition function of four-dimensional N=2* gauge theories as a concrete example, we demonstrate that each instanton sector in the very strongly coupled large-N limit is related to the one in the 't Hooft limit (N->Infinity with g^2 N fixed) through a simple analytic continuation. Furthermore we show the equivalence between the instanton partition functions of a pair of large-N gauge theories related by an orbifold projection. This can open up a new way to analyze the partition functions of low/non-supersymmetric theories. We also discuss implication of our result to gauge/gravity dualities for M-theory as well as a possible application to large-N QCD.

 Date/Place 8 Oct. (Tue.) 15:30～ / H711 Sinya Aoki (YITP) Nuclear potentials in QCD and their extensions (slides) We explain the HAL QCD method to extract nuclear potentials in QCD from NBS wave functions. In particular, a relation between the asymptotic behavior of NBS wave functions and the phase of the S-matrix in QCD is discussed in detail, and a formula to extract phase shifts of nucleon-nucleon scatterings is explained, together with some examples. Finally, we consider an extension of the method to more general cases, and some results obtained with the extension are presented.

 Date/Place 23 July (Tue.) 15:00～ / H711 Tomohisa Takimi (Tata Institute) Phase structures of Chern-Simons matter theories on S^2 \times S^1 (slides) As a new interesting class of AdS/CFT duality, 3d fundamental Chern-Simons matter theories can be dual descriptions of the Vasiliev's theory with higher spin symmetry which might be a strong clue for the quantum gravity. Analogous to the AdS/CFT correspondence between the deconfinement phase transition of large N gauge theory on spheres and the gravitational phase transition involving black-hole nucleation, we would be able to study phase structures of the Vasiliev's theory by elaborating phase structures of the Chern-Simons matter theory. Based on this motivation, I have studied phase structures of Chern-Simons matter theories with fundamental representation. In the fundamental Chern-Simons matter theories, due to the absence of the propagating degree of freedom of the gauge fields and by the topological magnetic flux, we can see new phases with saturated eigenvalue density function, which does not show up in the conventional Yang-Mills theories with the Gross-Witten-Wadia type phase transition.

 Date/Place 19 July (Fri.) 15:00～ / H711 Shigeki Sugimoto (IPMU) Confinement and Dynamical Symmetry Breaking in non-SUSY Gauge Theory from S-duality in String Theory (slides) We discuss an attempt to understand confinement and dynamical symmetry breaking in a 4-dimensional non-supersymmetric gauge theory using S-duality in type IIB string theory. The electric theory is a USp(2n) gauge theory and its magnetic dual is argued to be an SO(2n) or SO(2n-1) gauge theory. These theories are obtained as the low-energy effective theory of O3-D3bar systems in type IIB string theory, which are related by S-duality. Confinement and dynamical symmetry breaking in the USp(2n) gauge theory are caused by the condensation of scalar fields in the magnetic dual description, which is consistent with the scenario of the dual Meissner mechanism for the confinement. arXiv:1207.2203

 Date/Place 16 July (Tue.) 12:10～ / H711 Takeshi Morita (KEK) Black brane thermodynamics from supersymmetric field theories (slides) Through the gauge/gravity correspondence, the duality between the black branes and supersymmetric gauge theories has been predicted. In this seminar, I will reproduce the thermal free energies of the black Dp, M2 and M5 branes from the dual gauge theories through a simple estimation.There the supersymmetry plays a crucial role. Especially even the mysterious N^{3/2} and N^3 free energies of the M2 and M5 branes can be estimated, where N is the number of the branes. Since several assumptions are used in the derivation, the results are not rigid, but our study might provide an important clue to illuminate the questions: What is the essence of the gauge/gravity correspondence? What is the microscopic origin of the black hole thermodynamics? What is the dynamics of the M-branes at large N? arXiv:1305.0789

 Date/Place 9 July (Tue.) 15:00～ / H711 Heng-Yu Chen (NTU) A New 2d/4d correspondence from Integrability (slides) We will first describe various background materials, which we combine to lead to a new exact correspondence between 4 dimensional N=2 supersymmetric gauge theories and 2 dimensional N=(2,2) gauged linear sigma model. We will also comment on the various future directions and the seminar will aim to be pedagogical.

 Date/Place 25 Jun. (Tue.) 15:00～ / H711 Tetsuji Kimura (Rikkyo U.) Gauged Linear Sigma Model for Exotic Five-brane (slides) We study an N=(4,4) supersymmetric gauged linear sigma model which gives rise to the nonlinear sigma model for multi-centered KK-monopoles. We find a new T-duality transformation even in the presence of F-terms. Performing T-duality, we find a gauged linear sigma model whose IR limit describes an exotic five-brane with B-field. arXiv:1304.4061, 1305.4439

 Date/Place 18 Jun. (Tue.) 15:00～ / H711 Seiji Terashima (YITP) Brick Walls for Black Holes in AdS/CFT 我々は't Hooftによるブラックホールの煉瓦壁模型を ホログラフィック双対の立場から考察した。 (飯塚氏との近日中に投稿予定の共同研究に基づく。)

 Date/Place 11 Jun. (Tue.) 15:00～ / H711 Akinori Tanaka (Osaka U.) Exact calculation for AB-phase effective potential via supersymmetric localization (slides) When we consider a gauge theory on M x S1 spacetime, Aharonov-Bohm phases caused by non-simply connected extra dimension may develop non-vanishing expectation values. These phases induce dynamical symmetry breaking and this is called Hosotani mechanism. The way to break the symmetry depends on the effective potential for these phases. So far, the calculations for the effective potential rely on the perturbative theory. On the other hand, if we put the supersymmetric theory on the curved spacetime, we can apply supersymmetric localization principle to compute quantum effects. I would like to explain these mathematical techniques very briefly, and show some preliminary results on our computations for S2 x S1 spacetime. This is work in progress with A.Tomiya and T. Shimotani.

 Date/Place 4 Jun. (Tue.) 15:00～ / H711 Yoshimasa Hidaka (RIKEN) Generalization of the Nambu-Goldstone theorem (slides) Symmetry and its spontaneous breaking are of basic importance for understanding the low energy physics in many-body systems. When a continuum symmetry is spontaneously broken, there exist a zero mode called Nambu-Goldstone (NG) mode, which is well developed in Lorentz invariant systems. In contrast, in non-Lorentz invariant systems, the NG theorem has not been well developed. In this talk, we introduce the recent progress in generalization of NG theorem, and discuss the counting rule for NG modes using the Langevin equation derived from Mori's projection operator method. We show that the number of NG modes is equal to the number of broken charges, Qa, minus half the rank of the expectation value of [Qa,Qb]. We also discuss the spontaneous breaking of space-time symmetries.

 Date/Place 28 May. (Tue.) 15:00～ / H711 Takuya Shimotani (Osaka U.) Novel universality and Higgs decay H → γγ , gg in the SO(5) × U(1) gauge-Higgs unification (slides) The SO(5) × U(1) gauge-Higgs unification in the Randall–Sundrum warped space with the Higgs boson mass mH = 126 GeV is constructed. A universal relation is found between the Kaluza–Klein (KK) mass scale mKK and the Aharonov–Bohm (AB) phase θH in the fifth dimension. The cubic and quartic self-couplings of the Higgs boson become smaller than those in the standard model (SM), having universal dependence on θH. The decay rates H → γγ , gg are evaluated by summing contributions from KK towers. Corrections coming from KK excited states are finite and about 0.2% (2%) for θH = 0.12 (0.36), branching fractions of various decay modes of the Higgs boson remaining nearly the same as in the SM. The signal strengths of the Higgs decay modes relative to the SM are ∼ cos^2 θH. The mass of the first KK Z is predicted to be 5.9 (2.4) TeV for θH = 0.12 (0.36). The talk will mainly be based on Phys.Lett.B722(2013)94–99.

 Date/Place 21 May. (Tue.) 15:00～ / H711 Shinji Shimasaki (Kyoto U.) Exact results for perturbative partition functions of theories with SU(2|4) symmetry (slides) We study the theories with SU(2|4) symmetry which consist of the plane wave matrix model (PWMM), super Yang-Mills theory (SYM) on RxS^2 and SYM on RxS^3/Z_k. The last two theories can be realized as theories around particular vacua in PWMM, through the commutative limit of fuzzy sphere and Taylor's T-duality. We apply the localization method to PWMM to reduce the partition function and the expectation values of a class of supersymmetric operators to matrix integrals. By taking the commutative limit and performing the T-duality, we then obtain the matrix integrals for SYM on RxS^2 and SYM on RxS^3/Z_k. In this calculation, we ignore possible instanton effects and our matrix integrals describe the perturbative part exactly. We also discuss some applications of our results to gauge/gravity correspondence and little string theory on RxS^5.

 Date/Place 14 May. (Tue.) 15:00～/ H711 Norihiro Iizuka (YITP) Lessons from Black Holes in AdS/CFT We study some universal natures of black holes in holographic viewpoint. After showing the universal nature for fields around black holes, we discuss its implication for the holographic setting. This work is based on collaborations with S. Terashima (To appear).

 Date/Place 10 May. (Fri.) 15:00～16:30 / H711 Hirosi Ooguri (Caltech, Kavli IPMU) Dブレーンと量子雑音 TBA

 Date/Place 7 May. (Tue.) 15:00～ / H711 Yoichiro Nambu (Chicago U., Osaka U.) 流体力学の周辺 TBA

 Date/Place 30 Apr. (Tue.) 15:00～ / H711 Yuki Yokokura (Kyoto Univ.) A Self-consistent Model of the Black Hole Evaporation (slides) We construct a self-consistent model which describes a black hole from formation to evaporation including the back reaction from the Hawking radiation by using eikonal approximation and taking into account only s-wave of the radiation. In the case where a single null shell collapses, at the beginning the evaporation occurs, but it stops eventually, and a horizon and singularity appear. On the other hand, in the generic collapse process of a continuously distributed null matter, the black hole evaporates completely without forming a macroscopically large horizon nor singularity for large N case. We also find a stationary solution in the heat bath. [arXiv 1302.4733]

 Date/Place 23 Apr. (Tue.) 15:00～ / H711 Masanori Hanada (YITP) Large-Nc gauge theory and chiral random matrix theory (slides) We discuss how the $1/N_c$ expansion and the chiral random matrix theory ($\chi$RMT) can be used in the study of large-$N_c$ gauge theories. We first clarify the parameter region in which each of these two approaches is valid: while the fermion mass $m$ is fixed in the standard large-$N_c$ arguments ('t Hooft large-$N_c$ limit), $m$ must be scaled appropriately with a certain negative power of $N_c$ in order for the gauge theories to be described by the $\chi$RMT. Then, although these two limits are not compatible in general, we show that the breakdown of chiral symmetry can be detected by combining the large-$N_c$ argument and the $\chi$RMT with some cares. As a concrete example, we numerically study the four dimensional $SU(N_c)$ gauge theory with $N_f=2$ heavy adjoint fermions, introduced as the center symmetry preserver keeping the infrared physics intact, on a $2^4$ lattice. By looking at the low-lying eigenvalues of the Dirac operator for a massless probe fermion in the adjoint representation, we find that the chiral symmetry is indeed broken with the expected breaking pattern. This result reproduces a well-known fact that the chiral symmetry is spontaneously broken in the pure $SU(N_c)$ gauge theory in the large-$N_c$ and the large-volume limit, and therefore supports the validity of the combined approach. We also provide the interpretation of the gap and unexpected $N_c$-scaling, both of which are observed in the Dirac spectrum.

 Date/Place 16 Apr. (Tue.) 15:00～ / H711 Masato Taki (RIKEN) Holomorphic Blocks for 3d Gauge Theories (slides) Recent studies on supersymmetric localization have led to a lot of new exact solutions of gauge theories in diverse dimensions. 3d gauge theory is a focus of the most recent attention. In this talk I derive new explicit solutions to 3d N=2 gauge theories on the ellipsoid. I demonstrate that one can factorize these partition into the holomorphic blocks, which have been conjectured as building blocks of 3d theories. I In this way I prove the factorization conjecture for a range of 3d theories.

 Date/Place 9 Apr. (Tue.) 15:00～ / H711 Hidehiko Shimada (Okayama Institute for Quantum Physics) Membranes in the bulk from monopole operators of boundary ABJM theory (slides) In the talk, I will consider states with large angular momentum to facilitate the study of the M-theory regime of the AdS4/CFT3 correspondence (duality between M-theory on $AdS_4 \times S^7/Z_k$ and ABJM theory with gauge group $U(N)\times U(N)$ and level $k$, where $k$ is finite and $N$ is large). In particular I will discuss near-BPS operators in ABJM theory which correspond to states of membranes with large angular momenta on AdS. The talk will be based on my work with S. Kovacs(DIAS) and Y. Sato(Univ. Nagoya, KEK).