arXiv subjects

Yuya Sasai

Publications and source records attributed to Yuya Sasai.

12 recordsLinked to original sources

arXiv2016

Coulomb Branch Localization in Quiver Quantum Mechanics

We show how to exactly calculate the refined indices of N=4 U(1) times U(N) supersymmetric quiver quantum mechanics in the Coulomb branch by using the localization technique. The Coulomb branch localization is discussed from the viewpoint of both non-linear and gauged linear sigma models. A classification of fixed points in the Coulomb branch differs from one in the Higgs branch, but the derived indices completely agree with the results which were obtained by the localization in the Higgs branch. In the Coulomb branch localization, the refined indices can be written as a summation over different sets of the Coulomb branch fixed points. We also discuss a space-time picture of the fixed points in the Coulomb branch.

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arXiv2014

Exact Results in Quiver Quantum Mechanics and BPS Bound State Counting

We exactly evaluate the partition function (index) of N=4 supersymmetric quiver quantum mechanics in the Higgs phase by using the localization techniques. We show that the path integral is localized at the fixed points, which are obtained by solving the BRST equations, and D-term and F-term conditions. We turn on background gauge fields of R-symmetries for the chiral multiplets corresponding to the arrows between quiver nodes, but the partition function does not depend on these R-charges. We give explicit examples of the quiver theory including a non-coprime dimension vector. The partition functions completely agree with the mathematical formulae of the Poincare polynomials (chi_y-genus) and the wall crossing for the quiver moduli spaces . We also discuss exact computation of the expectation values of supersymmetric (Q-closed) Wilson loops in the quiver theory.

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arXiv2014

Compressible Fluids in the Membrane Paradigm: non-AdS Fluid/Gravity correspondences

Correspondences between black holes and fluids have been discussed in two different frameworks, the Fluid/Gravity correspondence and membrane paradigm. Recently, it has been discussed that these two theories can be understood as the same theory if the cutoff surface is placed slightly outside the horizon. The bulk viscosity is different for these two theories, but it does not contribute to physics since the fluid becomes incompressible in the near horizon limit. In the AdS/CFT correspondence, it is known that the fluid becomes compressible and the bulk viscosity is zero, apart from the near horizon limit. In this paper, we consider the Fluid/Gravity correspondence in asymptotically non-AdS geometries. We put the cutoff surface near but at a finite distance from the horizon. Then, the model becomes the membrane paradigm with compressible fluid. We show that the bulk viscosity is not negative at least within the linear response regime. We also discuss the higher derivative corrections in the stress-energy tensor.

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arXiv2013

Linear responses of D0-branes via gauge/gravity correspondence

We study linear responses of D0-branes in the low frequency region by using gauge/gravity correspondence. The dynamics of the D0-branes is described by Matrix theory with finite temperature, which is dual to a near extremal D0-brane black hole solution. We analyze the tensor mode and vector modes of a stress tensor and a Ramond-Ramond 1-form current of Matrix theory. Then, we show that if a cutoff surface is close to a horizon of the D0-brane black hole, the linear responses take forms similar to the hydrodynamic stress tensor and current on S^8. By taking a Rindler limit, those linear responses come to obey the hydrodynamics exactly, which is consistent with previous works on a Rindler fluid. We also show that if the cutoff surface is far from the horizon, the linear responses do not take the forms of the hydrodynamic stress tensor and current on S^8. Especially, we find that the vector modes no longer possess a diffusion pole in the low frequency region, which indicates that the linear responses of the D0-branes cannot be explained by hydrodynamics.

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arXiv2012

Transport coefficients of D1-D5-P system and the membrane paradigm

I discuss a correspondence between string theory and the black hole membrane paradigm in the context of the D1-D5-P system. By using the Kubo formula, I calculate transport coefficients of the effective string model induced by two kinds of minimal scalars. Then, I show that these transport coefficients exactly agree with the corresponding membrane transport coefficients of a five-dimensional near-extremal black hole with three charges.

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arXiv2011

Closed string transport coefficients and the membrane paradigm

I discuss a correspondence between a fictitious fluid in the black hole membrane paradigm and highly excited closed string states according to the black hole correspondence principle. I calculate the membrane transport coefficients of an electric NS-NS 2-charged black hole and transport coefficients of the highly excited closed string states which possess a Kaluza-Klein number and a winding number. Comparing both the transport coefficients at the correspondence point, I show that, except for the bulk viscosity, the membrane transport coefficients are of the same order as the transport coefficients of the closed string states on the stretched horizon. Also, I show that, except for the bulk viscosity, both the dimensionless transport coefficients, which are defined by dividing the transport coefficients by the entropy density, are exactly equal if the central charge is 6.

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arXiv2011

Shear viscosity of a highly excited string and the black hole membrane paradigm

Black hole membrane paradigm states that a certain viscous membrane seems to be sitting on a stretched horizon of a black hole from the viewpoint of a distant observer. We show that the shear viscosity of the fictitious membrane can be reproduced by a highly excited string covering the stretched horizon except for a numerical coefficient.

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arXiv2009

Massive particles coupled with 2+1 dimensional gravity and noncommutative field theory

Recently, it has been shown that the effective field theory of the Ponzano-Regge model with which spinless massive particles are coupled is given by three dimensional Euclidean noncommutative scalar field theory in the Lie algebraic noncommutative space [x^i, x^j]=2i kappa epsilon^{ijk}x_k (i,j,k=1,2,3) with kappa=4 pi G, where G is a gravitational constant. We examine whether there exists the relation between spinless massive particles coupled with 2+1 dimensional Einstein gravity and the Lorentzian version of the noncommutative field theory. Then, we point out that the momentum space of the spinless massive particles in 2+1 dimensional Einstein gravity is generally different from that of the noncommutative field theory, which is given by SL(2,R)/Z_2 group space.

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arXiv2009

The Cutkosky rule of three dimensional noncommutative field theory in Lie algebraic noncommutative spacetime

We investigate the unitarity of three dimensional noncommutative scalar field theory in the Lie algebraic noncommutative spacetime [x^i,x^j]=2i kappa epsilon^{ijk}x_k. This noncommutative field theory possesses a SL(2,R)/Z_2 group momentum space, which leads to a Hopf algebraic translational symmetry. We check the Cutkosky rule of the one-loop self-energy diagrams in the noncommutative phi^3 theory when we include a braiding, which is necessary for the noncommutative field theory to possess the Hopf algebraic translational symmetry at quantum level. Then, we find that the Cutkosky rule is satisfied if the mass is less than 1/(2^(1/2)kappa).

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arXiv2007

Domain wall solitons and Hopf algebraic translational symmetries in noncommutative field theories

Domain wall solitons are the simplest topological objects in field theories. The conventional translational symmetry in a field theory is the generator of a one-parameter family of domain wall solutions, and induces a massless moduli field which propagates along a domain wall. We study similar issues in braided noncommutative field theories possessing Hopf algebraic translational symmetries. As a concrete example, we discuss a domain wall soliton in the scalar phi^4 braided noncommutative field theory in Lie-algebraic noncommutative spacetime, [x^i,x^j]=2i kappa epsilon^{ijk}x_k (i,j,k=1,2,3), which has a Hopf algebraic translational symmetry. We first discuss the existence of a domain wall soliton in view of Derrick's theorem, and construct explicitly a one-parameter family of solutions in perturbation of the noncommutativity parameter kappa. We then find the massless moduli field which propagates on the domain wall soliton. We further extend our analysis to the general Hopf algebraic translational symmetry.

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arXiv2007

Braided quantum field theories and their symmetries

Braided quantum field theories proposed by Oeckl can provide a framework for defining quantum field theories having Hopf algebra symmetries. In quantum field theories, symmetries lead to non-perturbative relations among correlation functions. We discuss Hopf algebra symmetries and such relations in braided quantum field theories. We give the four algebraic conditions between Hopf algebra symmetries and braided quantum field theories, which are required for the relations to hold. As concrete examples, we apply our discussions to the Poincare symmetries of two examples of noncommutative field theories. One is the effective quantum field theory of three-dimensional quantum gravity coupled with spinless particles given by Freidel and Livine, and the other is noncommutative field theory on Moyal plane. We also comment on quantum field theory on kappa-Minkowski spacetime.

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arXiv2006

One-loop unitarity of scalar field theories on Poincare invariant commutative nonassociative spacetimes

We study scalar field theories on Poincare invariant commutative nonassociative spacetimes. We compute the one-loop self-energy diagrams in the ordinary path integral quantization scheme with Feynman's prescription, and find that the Cutkosky rule is satisfied. This property is in contrast with that of noncommutative field theory, since it is known that noncommutative field theory with space/time noncommutativity violates unitarity in the above standard scheme, and the quantization procedure will necessarily become complicated to obtain a sensible Poincare invariant noncommutative field theory. We point out a peculiar feature of the non-locality in our nonassociative field theories, which may explain the property of the unitarity distinct from noncommutative field theories. Thus commutative nonassociative field theories seem to contain physically interesting field theories on deformed spacetimes.

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