arXiv subjects

Yasuhiro Sekino

Publications and source records attributed to Yasuhiro Sekino.

At least 19 recordsLinked to original sources

arXiv2026

Holograms and Standard Models

Despite riddles, mysteries, and enigmas the theory of elementary particles has not changed for 50 years. We argue that the current paradigm -- Wilsonian quantum field theory -- is inadequate for resolving the puzzles, and should be replaced by a new paradigm based on the Holographic Principle. We show how a simplified but still very rich standard model emerges from de Sitter holography in the flat-space limit and explain why the puzzle of huge quantum corrections to the cosmological constant simply does not occur in the holographic paradigm.

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arXiv2025

DSSYK at Infinite Temperature: The Flat-Space Limit and the 't Hooft Model

In the limit of infinite radius de Sitter space becomes locally flat and the static patch tends to Rindler space. A holographic description of the static patch must result in a holographic description of some flat space theory, expressed in Rindler coordinates. Given such a holographic theory how does one decode the hologram and determine the bulk flat space theory, its particle spectrum, forces, and bulk quantum fields? In this paper we will answer this question for a particular case: DSSYK at infinite temperature and show that the bulk theory is a strongly coupled version of the 't Hooft model, i.e., (1+1)-dimensional QCD, with a single quark flavor. It may also be thought of as an open string theory with mesons lying on a single Regge trajectory.

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arXiv2025

Double-Scaled SYK, QCD, and the Flat Space Limit of de Sitter Space

A surprising connection exists between double-scaled SYK at infinite temperature, and large N QCD. The large N expansions of the two theories have the same form; the 't Hooft limit of QCD parallels the fixed p limit of SYK (for a theory with p-fermion interactions), and the limit of fixed gauge coupling g -- the flat space limit in AdS/CFT -- parallels the double-scaled limit of SYK. From the holographic perspective fixed g is the far more interesting limit of gauge theory, but very little is known about it. DSSYK allows us to explore it in a more tractable example. The connection is illustrated by perturbative and non-perturbative DSSYK calculations, and comparing the results with known properties of Yang Mills theory. The correspondence is largely independent of the conjectured duality between DSSYK and de Sitter space, but may have a good deal to tell us about it.

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arXiv2022

Rotating particles in AdS: Holography at weak gauge coupling and without conformal symmetry

We consider gauge/gravity correspondence between maximally supersymmetric Yang-Mills theory in ($p+1$) dimensions and superstring theory on the near-horizon limit of the D$p$-brane solution. The string-frame metric is AdS$_{p+1}\times S^{8-p}$ times a Weyl factor, and there is no conformal symmetry except for $p=3$. In a previous paper by one of the present authors, the free-field result of gauge theory has been reproduced from string theory for a particular operator which has angular momentum along $S^{8-p}$. In this paper, we extend this result to operators which have angular momenta along AdS$_{p+2}$. Our approach is based on a Euclidean formulation proposed by Dobashi, Shimada and Yoneya and on the "string bit" picture. We first show that the spinning string solution in Lorentzian AdS, found by Gubser, Klebanov and Polyakov, can be recast in a form which connects two points on the boundary of Euclidean AdS. Transition amplitudes of such strings can be interpreted as gauge theory correlators. We study the case of zero gauge coupling by ignoring interactions among string bits (massless particles in ten-dimensional spacetime which constitute a string), and show that the free-field results of gauge theory are reproduced.

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arXiv2019

Evidence for Gauge/Gravity Correspondence for D$p$-branes at Weak 't Hooft Coupling

We consider gauge/gravity correspondence for general Dp-branes with $0\le p\le 4$, namely, the duality between the (p+1)-dimensional maximally supersymmetric Yang-Mills theory and superstring theory on the near-horizon limit of the Dp-brane solution. It has been known that in the large N gauge theory at zero temperature and strong 't Hooft coupling, the two-point functions of operators corresponding to supergravity modes obey power-law, with a power different from the free-field value when $p\neq 3$. In this work, we show that the free-field result of gauge theory can be reproduced from the bulk string theory, for the two-point function of an operator Tr(Z^J), where Z is a complex combination of two scalar fields. We assume the spatial direction of worldsheet is discretized into J bits, and use the fact that these bits become independent particles when string tension is zero.

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arXiv2018

Observational signatures of dark energy produced in an ancestor vacuum: Forecast for galaxy surveys

We study observational consequences of the model for dark energy proposed in [1] (Aoki et al., Phys.Rev. D97 (2018) no.4, 043517). We assume our universe has been created by bubble nucleation, and consider quantum fluctuations of an ultralight scalar field. Residual effects of fluctuations generated in an ancestor vacuum (de Sitter space in which the bubble was formed) is interpreted as dark energy. Its equation of state parameter w(z) has a characteristic form, approaching -1 in the future, but -1/3 in the past. A novel feature of our model is that dark energy effectively increases the magnitude of the negative spatial curvature in the evolution of the Hubble parameter, though it does not alter the definition of the angular diameter distance. We perform Fisher analysis and forecast the constraints for our model from future galaxy surveys by Square Kilometre Array and Euclid. Due to degeneracy between dark energy and the spatial curvature, galaxy surveys alone can determine these parameters only for optimistic choices of their values, but combination with other independent observations, such as CMB, will greatly improve the chance of determining them.

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arXiv2018

Vacuum fluctuations in an ancestor vacuum: A possible dark energy candidate

We consider an open universe created by bubble nucleation, and study possible effects of an "ancestor vacuum" (de Sitter space in which bubble nucleation occurred) on the present universe. We compute vacuum expectation values of energy-momentum tensor for a minimally coupled scalar field, carefully taking into account the effect of the ancestor vacuum by the Euclidean prescription. In the study of the time evolution, an important role is played by the so-called supercurvature mode, which is non-normalizable on a spatial slice of open universe and decays in time most slowly. We point out that vacuum energy of a quantum field can be regarded as dark energy if mass of the field is of order the present Hubble parameter or smaller. We obtain preliminary results for the dark energy equation of state w(z) as a function of the redshift.

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arXiv2014

Evolution of vacuum fluctuations generated during and before inflation

We calculate the time evolution of the expectation value of the energy-momentum tensor for a minimally-coupled massless scalar field in cosmological spacetimes, with an application to dark energy in mind. We first study the evolution from inflation until the present, fixing the Bunch-Davies initial condition. The energy density of a quantum field evolves as $ρ\sim 3(H_I H)^2 /32 π^2 $ in the matter-dominated (MD) period, where $H_I$ and $H$ are the Hubble parameters during inflation and at each moment. Its equation of state, $w=ρ/p$, changes from a negative value to $w=1/3$ in the radiation-dominated period, and from $1/3$ to $w=0$ in the MD period. We then consider possible effects of a Planckian universe, which may have existed before inflation, by assuming there was another inflation with the Hubble parameter $H_P (> H_I)$. In this case, modes with wavelengths longer than the current horizon radius are mainly amplified, and the energy density of a quantum field grows with time as $ρ\sim (a/a_0)(H_P H)^2/32$ in the MD period, where $a$ and $a_0$ are the scale factors at each time and at present. Hence, if $H_P$ is of the order of the Planck scale $M_P$, $ρ$ becomes comparable to the critical density $3(M_P H)^2$ at the present time. The contribution to $ρ$ from the long wavelength fluctuations generated before the ordinary inflation has $w=-1/3$ in the free field approximation. We mention a possibility that interactions further amplify the energy density and change the equation of state.

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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

Possible origin of CMB temperature fluctuations: Vacuum fluctuations of Kaluza-Klein and string states during inflationary era

We point out that the temperature fluctuations of cosmic microwave background (CMB) can be generated in a way that is different from the one usually assumed in slow-roll inflation. Our mechanism is based on vacuum fluctuations of fields which are at rest at the bottom of the potential, such as Kaluza-Klein modes or string excited states. When there are a large number (typically of order $N\sim 10^{14}$) of fields with small mass in unit of Hubble parameter during the inflationary era, this effect can give significant contributions to the CMB temperature fluctuations. This number $N$ makes it possible to enhance scalar perturbation relative to tensor perturbation. Comparison with the observed amplitudes suggests that models with string scale of order $10^{-5}$ of 4D Planck scale are favorable.

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arXiv2011

CMB Fluctuations and String Compactification Scales

We propose a mechanism for the generation of temperature fluctuations of cosmic microwave background. We consider a large number of fields, such as Kaluza-Klein modes and string excitations. Each field contributes to the gravitational potential by a small amount, but an observable level of temperature fluctuations is achieved by summing up the contribution of typically of order 10^{14} fields. Tensor fluctuations are hardly affected by these fields. Our mechanism is based on purely quantum effects, and is different from the "slow-roll" or "curvaton" scenario. Using the observed data, we find constraints on the parameters of this model, such as the size of the extra dimensions and the string scale. Our model predicts a particular pattern of non-gaussianity with a small magnitude.

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arXiv2011

Direct test of the gauge-gravity correspondence for Matrix theory correlation functions

We study correlation functions in (0+1)-dimensional maximally supersymmetric U(N) Yang-Mills theory, which was proposed by Banks et al. as a non-perturbative definition of 11-dimensional M-theory in the infinite-momentum frame. We perform first-principle calculations using Monte Carlo simulations, and compare the results against the predictions obtained previously based on the gauge-gravity correspondence from 10 dimensions. After providing a self-contained review on these predictions, we present clear evidence that the predictions in the large-N limit actually hold even at small N such as N=2 and 3. The predicted behavior seems to continue to the far infrared regime, which goes beyond the naive range of validity of the 10D supergravity analysis. This suggests that the correlation functions also contain important information on the M-theory limit.

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arXiv2010

On the Topological Phases of Eternal Inflation

Eternal inflation is a term that describes a number of different phenomena which have been classified by Winitzki. According to Winitzki's classification these phases can be characterized by the topology of the percolating structures in the inflating, "white," region. In this paper we discuss these phases, the transitions between them, and the way they are seen by a "Census Taker"; a hypothetical observer inside the non-inflating, "black," region. We discuss three phases that we call, "black island," "tubular," and "white island." The black island phase is familiar, comprised of rare Coleman De Luccia bubble nucleation events. The Census Taker sees an essentially spherical boundary, described by the conformal field theory of the FRW/CFT correspondence. In the tubular phase the Census Taker sees a complicated infinite genus structure composed of arbitrarily long tubes. The white island phase is even more mysterious from the black side. Surprisingly, when viewed from the non-inflating region this phase resembles a closed, positively curved universe which eventually collapses to a singularity. Nevertheless, pockets of eternal inflation continue forever. In addition there is an "aborted" phase in which no eternal inflation takes place. Rigorous results of Chayes, Chayes, Grannan and Swindle establish the existence of all of these phases, separated by first order transitions, in Mandelbrot percolation, a simple model of eternal inflation.

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arXiv2010

Census Taking in the Hat: FRW/CFT Duality

In this paper a holographic description of eternal inflation is developed. We focus on the description of an open FRW universe that results from a tunneling event in which a false vacuum with positive vacuum energy decays to a supersymmetric vacuum with vanishing cosmological constant. The observations of a "Census Taker" in the final vacuum can be organized into a holographic dual conformal field theory that lives on the asymptotic boundary of space. We refer to this bulk-boundary correspondence as FRW/CFT duality. The dual CFT is a Euclidean two-dimensional theory that includes a Liouville 2-D gravity sector describing geometric fluctuations of the boundary. The RG flow of the theory is richer than in the ADS/CFT correspondence, and generates two space-time dimensions--one space-like and one time-like. We discuss a number of phenomena such as bubble collisions, and the Garriga, Guth, Vilenkin "persistence of memory," from the dual viewpoint.

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arXiv2009

Monte Carlo studies of Matrix theory correlation functions

We study correlation functions in (0+1)-dimensional maximally supersymmetric U(N) gauge theory, which represents the low-energy effective theory of D0-branes. In the large-N limit, the gauge-gravity duality predicts power-law behaviors in the infrared region for the two-point correlation functions of operators corresponding to supergravity modes. We evaluate such correlation functions on the gauge theory side by the Monte Carlo method. Clear power-law behaviors are observed at N=3, and the predicted exponents are confirmed consistently. Our results suggest that the agreement extends to the M-theory regime, where the supergravity analysis in 10 dimensions may not be justified a priori.

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arXiv2008

Fast Scramblers

We consider the problem of how fast a quantum system can scramble (thermalize) information, given that the interactions are between bounded clusters of degrees of freedom; pairwise interactions would be an example. Based on previous work, we conjecture: 1) The most rapid scramblers take a time logarithmic in the number of degrees of freedom. 2) Matrix quantum mechanics (systems whose degrees of freedom are n by n matrices) saturate the bound. 3) Black holes are the fastest scramblers in nature. The conjectures are based on two sources, one from quantum information theory, and the other from the study of black holes in String Theory.

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arXiv2008

Future Foam

We study pocket universes which have zero cosmological constant and non-trivial boundary topology. These arise from bubble collisions in eternal inflation. Using a simplified dust model of collisions we find that boundaries of any genus can occur. Using a radiation shell model we perform analytic studies in the thin wall limit to show the existence of geometries with a single toroidal boundary. We give plausibility arguments that higher genus boundaries can also occur. In geometries with one boundary of any genus a timelike observer can see the entire boundary. Geometries with multiple disconnected boundaries can also occur. In the spherical case with two boundaries the boundaries are separated by a horizon. Our results suggest that the holographic dual description for eternal inflation, proposed by Freivogel, Sekino, Susskind and Yeh, should include summation over the genus of the base space of the dual conformal field theory. We point out peculiarities of this genus expansion compared to the string perturbation series.

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arXiv2006

A Holographic Framework for Eternal Inflation

In this paper we provide some circumstantial evidence for a holographic duality between bubble nucleation in an eternally inflating universe and a Euclidean conformal field theory. The holographic correspondence (which is different than Strominger's dS/CFT duality) relates the decay of (3+1)-dimensional de Sitter space to a two-dimensional CFT. It is not associated with pure de Sitter space, but rather with Coleman-De Luccia bubble nucleation. Alternatively, it can be thought of as a holographic description of the open, infinite, FRW cosmology that results from such a bubble. The conjectured holographic representation is of a new type that combines holography with the Wheeler-DeWitt formalism to produce a Wheeler-DeWitt theory that lives on the spatial boundary of a k=-1 FRW cosmology. We also argue for a more ambitious interpretation of the Wheeler-DeWitt CFT as a holographic dual of the entire Landscape.

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