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James T. Liu

Publications and source records attributed to James T. Liu.

At least 73 records · Page 4Linked to original sources
arXiv2014

The shortened KK spectrum of IIB supergravity on Y^{p,q}

We examine the shortened KK spectrum of IIB supergravity compactified on Y^{p,q} and conjecture that the spectrum we have obtained is complete. The (untwisted) shortened spectrum on S^5/Z_{2p} and T^{1,1}/Z_p are obtained as special cases when p=q and q=0, respectively. Knowledge of the shortened spectrum allows us to compute the superconformal index of these theories and to find agreement with earlier calculations from the dual field theories. We also employ the shortened spectrum to perform a 1/N^2 test of AdS/CFT by holographically reproducing the difference of the central charges, c-a=p/8, of the dual CFTs.

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arXiv2014

Small Treatise on Spin-3/2 Fields and their Dual Spectral Functions

In this work we systematically study various aspects of spin-3/2 fields in a curved background. We mostly focus on a minimally coupled massive spin-3/2 field in arbitrary dimensions, and solve the equation of motion either explicitly or numerically in AdS, Schwarzschild-AdS and Reissner-Nordström-AdS backgrounds. Although not the main focus of this work, we also make a connection with the gravitino equation of motion in gauged supergravity. Motivated by the AdS/CFT correspondence, we emphasize calculational improvements and technical details of the dual spectral functions. We attempt to provide a coherent and comprehensive picture of the existing literature.

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arXiv2013

1/N^2 corrections to the holographic Weyl anomaly

We compute the O(1) contribution to holographic c-a for IIB supergravity on AdS_5 x S^5/Z_n and on AdS_5 x T^{1,1}/Z_n. In both cases, we find agreement with the dual field theory results, thus providing 1/N^2 checks of AdS/CFT with reduced supersymmetry. Since the holographic computation involves a sum over shortened multiplets in the KK tower, we provide some details on the S^5 and T^{1,1} spectra in a form that is convenient when considering their Z_n orbifolds. The computation for the even Z_n orbifolds of S^5 includes a sum over the multiplets in the twisted sector that is essential for obtaining agreement with the dual field theory.

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arXiv2013

What do non-relativistic CFTs tell us about Lifshitz spacetimes?

We study the reconstructability of (d+2)-dimensional bulk spacetime from (d+1)-dimensional boundary data, particularly concentrating on backgrounds which break (d+1)-dimensional Lorentz invariance. For a large class of such spacetimes, there exist null geodesics which do not reach the boundary. Therefore classically we expect some information is trapped in the bulk and thus invisible at the boundary. We show that this classical intuition correctly predicts the quantum situation: whenever there are null geodesics which do not reach the boundary, there are also "trapped scalar modes" whose boundary imprint is exponentially suppressed. We use these modes to show that no smearing function exists for pure Lifshitz spacetime, nor for any flow which includes a Lifshitz region. Indeed, for any (planar) spacetime which breaks (d+1)-dimensional Lorentz invariance at any radius, we show that local boundary data cannot reconstruct complete local bulk data.

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arXiv2013

Higher derivative corrections to Lifshitz backgrounds

We explore the effect of curvature-square corrections on Lifshitz solutions to the Einstein-Maxwell-dilaton system. After exhibiting the renormalized Lifshitz scaling solution to the system with parameterized R^2 corrections, we turn to a toy model with coupling g(ϕ)C_{μνρσ}^2 and demonstrate that such a term can both stabilize the dilaton and resolve the Lifshitz horizon to AdS_2 x R^2. As an example, we construct numerical flows from AdS_4 in the UV to an intermediate Lifshitz region and then to AdS_2 x R^2 in the deep IR.

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arXiv2013

The spectrum of IIB supergravity on AdS_5 x S^5/Z_3 and a 1/N^2 test of AdS/CFT

We present the complete Kaluza-Klein spectrum resulting from the compactification of IIB supergravity on S^5/Z_3. Knowledge of this spectrum allows us to perform a holographic computation of the difference of central charges c-a of the dual SU(N)^3 quiver gauge theory. We find the numerical value c-a=3/16, in exact agreement with the field theory result.

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arXiv2013

Higher-derivative couplings in string theory: dualities and the B-field

The first quantum correction to the IIA string effective action arises at the eight-derivative level and takes the schematic form (t_8 t_8 - 1/8 εε)R^4 + B_2 \wedge X_8. This correction, however, cannot be complete by itself, as it is neither supersymmetric nor T-duality covariant. We reexamine these eight-derivative couplings and conjecture that the simple replacement R -> R(Ω_+), where Ω_+ = Ω+ 1/2 H is the connection with torsion, nearly completely captures their dependence on the B-field. The exception is in the odd-odd spin structure sector, where additional terms are needed. We present here a complete result at the level of the five-point function and a partial one for the six-point function. Further evidence for this conjecture comes from considering T-duality as well as heterotic/IIA duality beyond leading order. Finally, we discuss the eleven-dimensional lift of the modified one-loop type IIA couplings.

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arXiv2012

Rigid Supersymmetric Backgrounds of Minimal Off-Shell Supergravity

We discuss various aspects of rigid supersymmetry within minimal N=1 off-shell supergravity using the old and new minimal formulations both in Lorentzian and Euclidean signatures. In particular, we construct all rigid supersymmetry backgrounds with a hypersurface orthogonal Killing vector. In the Lorentzian signature we show that AdS_4 provides a rigid supersymmetric background in both formulations albeit with different amounts of preserved supersymmetry. In the Euclidean signature we find new backgrounds of the old-minimal supergravity, including squashed four-spheres and a half-BPS version of flat space.

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arXiv2012

Supersymmetry of consistent massive truncations of IIB supergravity

We discuss the supersymmetry and fermionic sector of the recently obtained consistent truncations of IIB supergravity containing massive modes. In particular, we present the general form of the five-dimensional N = 4 supersymmetry transformations and equations of motion for the fermions arising in the reduction of IIB theory on T^{1,1} which contains all modes invariant under the SU(2) x SU(2) isometry group. The N = 4 reduction can be further truncated to two different N = 2 sub-sectors. For each of these, we present the N = 2 fermionic supersymmetry transformations and corresponding superpotentials. As an application, we obtain the explicit Killing spinors of the Klebanov-Strassler solution and comment on the relation to the ansatz of Papadopoulos and Tseytlin. We also demonstrate the applicability of consistent truncations on squashed Sasaki-Einstein manifolds to a class of flux compactifications, focusing on a recent solution describing the geometry of gaugino condensation on wrapped D7 branes and which possesses dynamic SU(2) structure.

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arXiv2012

Holographic Lifshitz flows and the null energy condition

We study asymptotically Lifshitz spacetimes and the constraints on flows between Lifshitz fixed points imposed by the null energy condition. In contrast with the relativistic holographic c-theorem, where the effective AdS radius, L, is monotonically decreasing in the IR, for Lifshitz backgrounds we find that both L and z may flow in either direction. We demonstrate this with several numerical examples in a phenomenological model with a massive gauge field coupled to a real scalar.

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arXiv2012

On N = 2 Truncations of IIB on T^{1,1}

We study the N=4 gauged supergravity theory which arises from the consistent truncation of IIB supergravity on the coset T^{1,1}. We analyze three N=2 subsectors and in particular we clarify the relationship between true superpotentials for gauged supergravity and certain fake superpotentials which have been widely used in the literature. We derive a superpotential for the general reduction of type I supergravity on T^{1,1} and this together with a certain solution generating symmetry is tantamount to a superpotential for the baryonic branch of the Klebanov-Strassler solution.

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arXiv2012

Holographic c-theorems and higher derivative gravity

In AdS/CFT, the holographic Weyl anomaly computation relates the a-anomaly coefficient to the properties of the bulk action at the UV fixed point. This universal behavior suggests the possibility of a holographic c-theorem for the a-anomaly under flows to the IR. We prove such a c-theorem for higher curvature Lovelock gravity, where the bulk equations of motion remain second order. We also explore f(R) gravity as a toy model where higher derivatives cannot be avoided. In this case, monoticity of the flow requires an additional condition related to the higher derivative nature of the theory. This is in contrast to the case of f(R) black hole entropy, where the second law follows from application of the full Einstein equations and the null energy condition.

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arXiv2011

A holographic c-theorem for higher derivative gravity

We prove a holographic c-theorem for the a central charge in AdS/CFT where the bulk is described by a gravitational action built out of an arbitrary function f(R^{ab}_{cd}) of the Riemann tensor coupled to bulk matter. This theorem holds provided a generalized null energy condition involving both matter and higher curvature gravitational interactions is satisfied. As an example, we consider the case of a curvature-squared action, and find that generically the generalized null energy condition involves not just the bulk matter, but also the sign of R" where a prime denotes a radial derivative and where R is the bulk scalar curvature.

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arXiv2011

Supersymmetric massive truncations of IIb supergravity on Sasaki-Einstein manifolds

Motivated by recent interest in applications of the AdS/CFT correspondence to condensed matter applications involving fermions, we present the supersymmetric completion of the recent massive truncations of IIB supergravity on Sasaki-Einstein manifolds. In particular, we reduce the fermionic sector of IIB supergravity to obtain five dimensional N=2 supergravity coupled to one hypermultiplet and one massive vector multiplet. The supersymmetry transformations and equations of motion are presented and analyzed. Finally, a particularly interesting truncation to N=2 supergravity coupled to a single hypermultiplet is presented which is the supersymmetric completion of the recently constructed bosonic theory dual to a 3+1 dimensional system exhibiting a superconducting phase transition.

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arXiv2010

Computing 1/N^2 corrections in AdS/CFT

Stringy corrections in AdS/CFT generally fall into the category of either α' effects or string loop effects, corresponding to 1/λand 1/N corrections, respectively, in the dual field theory. While α'^3R^4 corrections have been well studied, at least in the context of N=4 super-Yang-Mills, less is known about the 1/N^2 corrections arising from closed string loops. In this paper, we consider AdS_5 x SE_5 compactifications of the IIB string, and compute the closed string loop correction to the anomaly coefficients a and c in the dual field theory. For T^{1,1} reductions, we find the string loop correction to yield c-a=1/24, which is the contribution to c-a of a free N=2 hypermultiplet. We also comment on reductions to lower dimensional AdS theories as well as the nature of T-duality with higher derivatives.

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arXiv2010

Consistent massive truncations of IIB supergravity on Sasaki-Einstein manifolds

Recent work on holographic superconductivity and gravitational duals of systems with non-relativistic conformal symmetry have made use of consistent truncations of D=10 and D=11 supergravity retaining some massive modes in the Kaluza-Klein tower. In this paper we focus on reductions of IIB supergravity to five dimensions on a Sasaki-Einstein manifold, and extend these previous truncations to encompass the entire bosonic sector of gauged D=5, N=2 supergravity coupled to massive multiplets up to the second Kaluza-Klein level. We conjecture that a necessary condition for the consistency of massive truncations is to only retain the lowest modes in the massive trajectories of the Kaluza-Klein mode decomposition of the original fields. This is an extension of the well-known result that consistent truncations may be obtained by restricting to the singlet sector of the internal symmetry group.

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arXiv2009

Higher Derivative Corrections to R-charged Black Holes: Boundary Counterterms and the Mass-Charge Relation

We carry out the holographic renormalization of Einstein-Maxwell theory with curvature-squared corrections. In particular, we demonstrate how to construct the generalized Gibbons-Hawking surface term needed to ensure a perturbatively well-defined variational principle. This treatment ensures the absence of ghost degrees of freedom at the linearized perturbative order in the higher-derivative corrections. We use the holographically renormalized action to study the thermodynamics of R-charged black holes with higher derivatives and to investigate their mass to charge ratio in the extremal limit. In five dimensions, there seems to be a connection between the sign of the higher derivative couplings required to satisfy the weak gravity conjecture and that violating the shear viscosity to entropy bound. This is in turn related to possible constraints on the central charges of the dual CFT, in particular to the sign of c-a.

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