arXiv subjects

James T. Liu

Publications and source records attributed to James T. Liu.

At least 91 records · Page 5Linked to original sources

arXiv2009

The Partition Function of a Wilson Loop in a Strongly Coupled $\mathcal N=4$ Supersymmetric Yang-Mills Plasma with Fluctuations

We examine the one-loop partition function describing the fluctuations of the superstring in a Schwarzschild-AdS$_5\times S^5$ background. On the bosonic side, we demonstrate the one-loop equivalence of the Nambu-Goto action and the Polyakov action for a general worldsheet, while on the fermionic side, we consider the reduction of the ten-dimensional Green-Schwarz fermion action to a two-dimensional worldsheet action. We derive the partition functions of the worldsheets corresponding to both straight and parallel Wilson lines. We show that the UV divergences of the functional determinants in the thermal AdS background are canceled.

hep-th↗

arXiv2009

Black holes in five-dimensional gauged supergravity with higher derivatives

We examine five-dimensional $\mathcal N=2$ gauged supergravity including terms up to four derivatives. These additional terms correspond to the supersymmetric completion of $R^2$, and were originally obtained in hep-th/0611329 using conformal supergravity techniques. Here we integrate out the auxiliary fields and obtain the on-shell action for minimal supergravity with such corrections. We then construct $R$-charged AdS black holes to linear order in the four derivative terms and investigate the effect of these corrections on their thermodynamical properties. Finally, we relate the geometrical coefficients governing the four-derivative corrections to gauge theory data using holographic anomaly matching. This enables us to obtain a microscopic expression for the entropy of the solutions.

hep-th↗

arXiv2009

Higher derivative effects on eta/s at finite chemical potential

We examine the effects of higher derivative corrections on eta/s, the ratio of shear viscosity to entropy density, in the case of a finite R-charge chemical potential. In particular, we work in the framework of five-dimensional N =2 gauged supergravity, and include terms up to four derivatives, representing the supersymmetric completion of the Chern-Simons term A \wedge Tr (R \wedge R). The addition of the four-derivative terms yields a correction which is a 1/N effect, and in general gives rise to a violation of the eta/s bound. Furthermore, we find that, once the bound is violated, turning on the chemical potential only leads to an even larger violation of the bound.

hep-th↗

arXiv2008

Slow nucleation rates in Chain Inflation with QCD Axions or Monodromy

The previous proposal (by two of us) of chain inflation with the QCD axion is shown to fail. The proposal involved a series of fast tunneling events, yet here it is shown that tunneling is too slow. We calculate the bubble nucleation rates for phase transitions in the thick wall limit, approximating the barrier by a triangle. A similar problem arises in realization of chain inflation in the string landscape that uses series of minima along the monodromy staircase around the conifold point. The basic problem is that the minima of the potential are too far apart to allow rapid enough tunneling in these two models. We entertain the possibility of overcoming this problem by modifying the gravity sector to a Brans-Dicke theory. However, one would need extremely small values for the Brans-Dicke parameter. Many successful alternatives exist, including other "axions" (with mass scales not set by QCD) or potentials with comparable heights and widths that do not suffer from the problem of slow tunneling and provide successful candidates for chain inflation.

hep-ph↗

arXiv2008

Higher derivative corrections to R-charged AdS_5 black holes and field redefinitions

We consider four-derivative corrections to the bosonic sector of five-dimensional N=2 gauged supergravity. Since this theory includes the N=2 graviphoton, we consider both curvature and graviphoton field-strength terms that show up at the four-derivative level. We construct, to linear order, the higher-derivative corrections to the non-rotating R-charged AdS_5 black hole and demonstrate how this solution transforms under field redefinitions.

hep-th↗

arXiv2008

Hamilton-Jacobi Counterterms for Einstein-Gauss-Bonnet Gravity

The on-shell gravitational action and the boundary stress tensor are essential ingredients in the study of black hole thermodynamics. We employ the Hamilton-Jacobi method to calculate the boundary counterterms necessary to remove the divergences and allow the study of the thermodynamics of Einstein-Gauss-Bonnet black holes.

hep-th↗

arXiv2007

Bubbling AdS and droplet descriptions of BPS geometries in IIB supergravity

This paper focuses on supergravity duals of BPS states in N=4 super Yang-Mills. In order to describe these duals, we begin with a sequence of breathing mode reductions of IIB supergravity: first on S^3, then S^3 x S^1, and finally on S^3 x S^1 x CP^1. We then follow with a complete supersymmetry analysis, yielding 1/8, 1/4 and 1/2 BPS configurations, respectively (where in the last step we take the Hopf fibration of S^3). The 1/8 BPS geometries, which have an S^3 isometry and are time-fibered over a six-dimensional base, are determined by solving a non-linear equation for the Kahler metric on the base. Similarly, the 1/4 BPS configurations have an S^3 x S^1 isometry and a four-dimensional base, whose Kahler metric obeys another non-linear, Monge-Ampere type equation. Despite the non-linearity of the problem, we develop a universal bubbling AdS description of these geometries by focusing on the boundary conditions which ensure their regularity. In the 1/8 BPS case, we find that the S^3 cycle shrinks to zero size on a five-dimensional locus inside the six-dimensional base. Enforcing regularity of the full solution requires that the interior of a smooth, generally disconnected five-dimensional surface be removed from the base. The AdS_5 x S^5 ground state corresponds to excising the interior of an S^5, while the 1/8 BPS excitations correspond to deformations (including topology change) of the S^5 and/or the excision of additional droplets from the base. In the case of 1/4 BPS configurations, by enforcing regularity conditions, we identify three-dimensional surfaces inside the four-dimensional base which separate the regions where the S^3 shrinks to zero size from those where the S^1 shrinks.

hep-th↗

arXiv2007

Coupling constant dependence of the shear viscosity in N=4 supersymmetric Yang-Mills theory

Gauge theory - gravity duality predicts that the shear viscosity of N=4 supersymmetric SU(N_c) Yang-Mills plasma at temperature T in the limit of large N_c and large 't Hooft coupling g^2_{YM} N_c is independent of the coupling and equals to πN_c^2 T^3/8. In this paper, we compute the leading correction to the shear viscosity in inverse powers of 't Hooft coupling using the α'-corrected low-energy effective action of type IIB string theory. We also find the correction to the ratio of shear viscosity to the volume entropy density (equal to 1/4πin the limit of infinite coupling). The correction to 1/4πscales as (g^2_{YM} N_c)^{-3/2} with a positive coefficient.

hep-th↗

arXiv2007

New supersymmetric solutions of N=2, D=5 gauged supergravity with hyperscalars

We construct new supersymmetric solutions, including AdS bubbles, in an N=2 truncation of five-dimensional N=8 gauged supergravity. This particular truncation is given by N=2 gauged supergravity coupled to two vector multiples and three incomplete hypermultiplets, and was originally investigated in the context of obtaining regular AdS bubble geometries with multiple active R-charges. We focus on cohomogeneity-one solutions corresponding to objects with two equal angular momenta and up to three independent R-charges. Curiously, we find a new set of zero and negative mass solitons asymptotic to AdS_5/Z_k, for k \ge 3, which are everywhere regular without closed timelike curves.

hep-th↗

arXiv2007

Bubbling AdS Black Holes

We explore the non-BPS analog of `AdS bubbles', which are regular spherically symmetric 1/2 BPS geometries in type IIB supergravity. They have regular horizons and can be thought of as bubbling generalizations of non-extremal AdS black hole solutions in five-dimensional gauged supergravity. Due to the appearance of the Heun equation even at the linearized level, various approximation and numerical methods are needed in order to extract information about this system. We study how the vacuum expectation value and mass of a particular dimension two chiral primary operator depend on the temperature and chemical potential of the thermal Yang-Mills theory. In addition, the mass of the bubbling AdS black holes is computed. As is shown numerically, there are also non-BPS solitonic bubbles which are completely regular and arise from continuous deformations of BPS AdS bubbles.

hep-th↗

arXiv2007

Gauged supergravity from type IIB string theory on Y^{p,q} manifolds

We first construct a consistent Kaluza-Klein reduction ansatz for type IIB theory compactified on Sasaki-Einstein manifolds Y^{p,q} with Freund-Rubin 5-form flux giving rise to minimal N=2 gauged supergravity in five dimensions. We then investigate the R-charged black hole solution in this gauged supergravity, and in particular study its thermodynamics. Based on the gauge theory/string theory correspondence, this non-extremal geometry is dual to finite temperature strongly coupled four-dimensional conformal gauge theory plasma with a U(1)_R-symmetry charge chemical potential. We study transport properties of the gauge theory plasma and show that the ratio of shear viscosity to entropy density in this plasma is universal. We further conjecture that the universality of shear viscosity of strongly coupled gauge theory plasma extends to nonzero R-charge chemical potential.

hep-th↗

arXiv2007

Thermodynamics of the N=2^* strongly coupled plasma

Gauge/string duality is a potentially important framework for addressing the properties of the strongly coupled quark gluon plasma produced at RHIC. However, constructing an actual string theory dual to QCD has so far proven elusive. In this paper, we take a partial step towards exploring the QCD plasma by investigating the thermodynamics of a non-conformal system, namely the N=2^* theory, which is obtained as a mass deformation of the conformal N=4 gauge theory. We find that at temperatures of order the mass scale, the thermodynamics of the mass deformed plasma is surprisingly close to that of the conformal gauge theory plasma. This suggests that many properties of the quark gluon plasma at RHIC may in fact be well described by even relatively simple models such as that of the conformal N=4 plasma.

hep-th↗

arXiv2007

Finite Heisenberg Groups from Nonabelian Orbifold Quiver Gauge Theories

A large class of orbifold quiver gauge theories admits the action of finite Heisenberg groups of the form \prod_i Heis(Z_{q_i} x Z_{q_i}). For an Abelian orbifold generated by Γ, the Z_{q_i} shift generator in each Heisenberg group is one cyclic factor of the Abelian group Γ. For general non-Abelian Γ, however, we find that the shift generators are the cyclic factors in the Abelianization of Γ. We explicitly show this for the case Γ=Δ(27), where we construct the finite Heisenberg group symmetries of the field theory. These symmetries are dual to brane number operators counting branes on homological torsion cycles, which therefore do not commute. We compare our field theory results with string theory states and find perfect agreement.

hep-th↗

arXiv2006

Chain Inflation via Rapid Tunneling in the Landscape

Chain inflation takes place in the string theory landscape as the universe tunnels rapidly through a series of ever lower energy vacua such as may be characterized by quantized changes in four form fluxes. The string landscape may be well suited to an early period of rapid tunneling, as required by chain inflation, followed by a later period of slow tunneling, such as may be required to explain today's dark energy and small cosmological constant. Each tunneling event (which can alternatively be thought of as a nucleation of branes) provides a fraction of an e-folding of inflation, so that hundreds of tunneling events provide the requisite amount of inflation. A specific example from M-theory compactification on manifolds with non-trivial three-cycles is presented.

hep-th↗

arXiv2006

All 1/2 BPS solutions of IIB supergravity with SO(4) x SO(4) isometry

In hep-th/0409174, Lin, Lunin and Maldacena constructed a set of regular 1/2 BPS geometries in IIB theory. These remarkable `bubbling AdS' geometries have a natural interpretation as duals of chiral primary operators with weight Delta=J in N=4 super-Yang Mills theory. Although these geometries have been assumed to be complete, from a purely supergravity point of view, additional 1/2 BPS configurations may potentially exist with a preferred null isometry. We explore this possibility and prove that the only additional class of 1/2 BPS solutions with SO(4) x SO(4) isometry are the familiar IIB pp-waves.

hep-th↗

arXiv2006

Mapping the G-structures and supersymmetric vacua of five-dimensional N=4 supergravity

We classify the supersymmetric vacua of N=4, d=5 supergravity in terms of G-structures. We identify three classes of solutions: with R^3, SU(2) and generic SO(4) structure. Using the Killing spinor equations, we fully characterize the first two classes and partially solve the latter. With the N=4 graviton multiplet decomposed in terms of N=2 multiplets: the graviton, vector and gravitino multiplets, we obtain new supersymmetric solutions corresponding to turning on fields in the gravitino multiplet. These vacua are described in terms of an SO(5) vector sigma-model coupled with gravity, in three or four dimensions. A new feature of these N=4 vacua, which is not seen from an N=2 point of view, is the possibility for preserving more exotic fractions of supersymmetry. We give a few concrete examples of these new supersymmetric (albeit singular) solutions. Additionally, we show how by truncating the N=4, d=5 set of fields to minimal supergravity coupled with one vector multiplet we recover the known two-charge solutions.

hep-th↗

arXiv2006

Finite Heisenbeg Groups and Seiberg Dualities in Quiver Gauge Theories

A large class of quiver gauge theories admits the action of finite Heisenberg groups of the form Heis(Z_q x Z_q). This Heisenberg group is generated by a manifest Z_q shift symmetry acting on the quiver along with a second Z_q rephasing (clock) generator acting on the links of the quiver. Under Seiberg duality, however, the action of the shift generator is no longer manifest, as the dualized node has a different structure from before. Nevertheless, we demonstrate that the Z_q shift generator acts naturally on the space of all Seiberg dual phases of a given quiver. We then prove that the space of Seiberg dual theories inherits the action of the original finite Heisenberg group, where now the shift generator Z_q is a map among fields belonging to different Seiberg phases. As examples, we explicitly consider the action of the Heisenberg group on Seiberg phases for C^3/Z_3, Y^{4,2} and Y^{6,3} quiver.

hep-th↗

arXiv2006

Central Extensions of Finite Heisenberg Groups in Cascading Quiver Gauge Theories

Many conformal quiver gauge theories admit nonconformal generalizations. These generalizations change the rank of some of the gauge groups in a consistent way, inducing a running in the gauge couplings. We find a group of discrete transformation that acts on a large class of these theories. These transformations form a central extension of the Heisenberg group, generalizing the Heisenberg group of the conformal case, when all gauge groups have the same rank. In the AdS/CFT correspondence the nonconformal quiver gauge theory is dual to supergravity backgrounds with both five-form and three-form flux. A direct implication is that operators counting wrapped branes satisfy a central extension of a finite Heisenberg group and therefore do not commute.

hep-th↗