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James T. Liu

Publications and source records attributed to James T. Liu.

At least 127 records · Page 7Linked to original sources
arXiv2003

Fine Tuning and Six-Dimensional Gauged $N=(1,0)$ Supergravity Vacua

We find a new family of supersymmetric vacuum solutions in the six-dimensional chiral gauged N=(1,0) supergravity theory. They are generically of the form AdS_3 x S^3, where the 3-sphere is squashed homogeneously along its Hopf fibres. The squashing is freely adjustable, corresponding to changing the 3-form charge, and the solution is supersymmetric for all squashings. In a limit where the length of the Hopf fibres goes to zero, one recovers, after a compensating rescaling of the fibre coordinate, a solution that is locally the same as the well-known (Minkowski)_4 x S^2 vacuum of this theory. It can now be viewed as a fine tuning of the new more general family. The traditional "Cosmological Constant Problem" is replaced in this theory by the problem of why the four-dimensional (Minkowski)_4 x S^2 vacuum should be selected over other members of the equally supersymmetric AdS_3 x S^3 family. We also obtain a family of dyonic string solutions in the gauged N=(1,0) theory, whose near-horizon limits approach the AdS_3 times squashed S^3 solutions.

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arXiv2003

Hidden Spacetime Symmetries and Generalized Holonomy in M-theory

In M-theory vacua with vanishing 4-form F, one can invoke the ordinary Riemannian holonomy H \subset SO(1,10) to account for unbroken supersymmetries n=1, 2, 3, 4, 6, 8, 16, 32. However, the generalized holonomy conjecture, valid for non-zero F, can account for more exotic fractions of supersymmetry, in particular 16<n<32. The conjectured holonomies are given by H \subset G where G are the generalized structure groups G=SO(d-1,1) x G(spacelike), G=ISO(d-1) x G(null) and G=SO(d) x G(timelike) with 1<=d<11. For example, G(spacelike)=SO(16), G(null)=[SU(8) x U(1)] \ltimes R^{56} and G(timelike)=SO*(16) when d=3. Although extending spacetime symmetries, there is no conflict with the Coleman-Mandula theorem. The holonomy conjecture rules out certain vacua which are otherwise permitted by the supersymmetry algebra.

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arXiv2003

Thermodynamics of the N=2* flow

We discuss the thermodynamics of the N=2*, SU(N) gauge theory at large 't Hooft coupling. The tool we use is the non-extremal deformation of the supergravity solution of Pilch and Warner (PW) [hep-th/0004063], dual to N=4, SU(N) gauge theory softly broken to N=2. We construct the exact non-extremal solution in five-dimensional gauged supergravity and further uplift it to ten dimensions. Turning to the thermodynamics, we analytically compute the leading correction in m/T to the free energy of the non-extremal D3 branes due to the PW mass deformation, and find that it is positive. We also demonstrate that the mass deformation of the non-extremal D3 brane geometry induces a temperature dependent gaugino condensate. We find that the standard procedure of extracting the N=2* gauge theory thermodynamic quantities from the dual supergravity leads to a violation of the first law of thermodynamics. We speculate on a possible resolution of this paradox.

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arXiv2003

Consistent reductions of IIB*/M* theory and de Sitter supergravity

We construct consistent non-linear Kaluza Klein reduction ansatze for a subset of fields arising from the reduction of IIB* and M* theory on dS_5 x H^5 and dS_4 x AdS_7, respectively. These reductions yield four and five-dimensional de Sitter supergravities, albeit with wrong sign kinetic terms. We also demonstrate that the ansatze may be used to lift multi-centered de Sitter black hole solutions to ten and eleven dimensions. The lifted dS_5 black holes correspond to rotating E4-branes of IIB* theory.

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arXiv2003

On Horizons and Plane Waves

We investigate the possibility of having an event horizon within several classes of metrics that asymptote to the maximally supersymmetric IIB plane wave. We show that the presence of a null Killing vector (not necessarily covariantly constant) implies an effective separation of the Einstein equations into a standard and a wave component. This feature may be used to generate new supergravity solutions asymptotic to the maximally supersymmetric IIB plane wave, starting from standard seed solutions such as branes or intersecting branes in flat space. We find that in many cases it is possible to preserve the extremal horizon of the seed solution. On the other hand, non-extremal deformations of the plane wave solution result in naked singularities. More generally, we prove a no-go theorem against the existence of horizons for backgrounds with a null Killing vector and which contain at most null matter fields. Further attempts at turning on a nonzero Hawking temperature by introducing additional matter have proven unsuccessful. This suggests that one must remove the null Killing vector in order to obtain a horizon. We provide a perturbative argument indicating that this is in fact possible.

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arXiv2002

Linearized Gravity in the Karch-Randall Braneworld

We present a linearized gravity investigation of the bent braneworld, where an AdS_4 brane is embedded in AdS_5. While we focus on static spherically symmetric mass distributions on the brane, much of the analysis continues to hold for more general configurations. In addition to the identification of the massive Karch-Randall graviton and a tower of Kaluza-Klein gravitons, we find a radion mode that couples to the trace of the energy-momentum tensor on the brane. The Karch-Randall radion arises as a property of the embedding of the brane in the bulk space, even in the context of a single brane model.

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arXiv2002

The Radion Mode in Consistent Brane-World Reductions

We construct consistent brane-world Kaluza-Klein reductions involving the radion mode that measures the separation of the domain-wall branes. In these new examples, we can obtain matter supermultiplets coupled to supergravity on the brane, starting from pure gauged supergravity in the higher dimension. This contrasts with previously-known examples of consistent brane-world reductions involving the radion, where either pure supergravity reduced to pure supergravity, or else supergravity plus matter reduced to supergravity plus matter. As well as considering supersymmetric reductions, we also show that there exist broader classes of consistent reductions of bosonic systems. These include examples where the lower-dimensional theory has non-abelian Yang-Mills fields and yet the scalar sector has a potential that admits Minkowski spacetime as a solution. Combined with a sphere reduction to obtain the starting point for the brane-world reduction, this provides a Kaluza-Klein mechanism for obtaining non-abelian gauge symmetries from the geometry of the reduction, whilst still permitting a Minkowski vacuum in the lower dimension.

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arXiv2002

Quantum Discontinuity for Massive Spin 3/2 with a Lambda Term

We show that the recently demonstrated absence of the van Dam-Veltman-Zakharov discontinuity for massive spin 3/2 with a Lambda term is an artifact of the tree level approximation, and that the discontinuity reappears at one loop. As a numerical check on the calculation, we rederive the vanishing of the one- loop beta function for D=11 supergravity on AdS_4 x S^7 level-by-level in the Kaluza-Klein tower.

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arXiv2002

Angular Momentum Mixing in Crystalline Color Superconductivity

In crystalline color superconductivity, quark pairs form at non-zero total momentum. This crystalline order potentially enlarges the domain of color superconductivity in cold dense quark matter. We present a perturbative calculation of the parameters governing the crystalline phase and show that this is indeed the case. Nevertheless, the enhancement is modest, and to lowest order is independent of the strength of the color interaction.

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arXiv2001

Exact multi-membrane solutions in AdS_7

We study the properties of an exact multi-membrane solution in seven-dimensional maximal SO(5)-gauged supergravity. Unlike previously known multi-centered solutions, the present one is asymptotically anti-de Sitter. We show that this multi-membrane configuration preserves only a quarter of the supersymmetries. When lifted to eleven dimensions, this solution is interpreted as a set of open membranes ending on self-dual strings on a stack of M5-branes, in the near M5 limit.

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arXiv2001

A New Fractional D2-brane, G_2 Holonomy and T-duality

Recently, a new example of a complete non-compact Ricci-flat metric of G_2 holonomy was constructed, which has an asymptotically locally conical structure at infinity with a circular direction whose radius stabilises. In this paper we find a regular harmonic 3-form in this metric, which we then use in order to obtain an explicit solution for a fractional D2-brane configuration. By performing a T-duality transformation on the stabilised circle, we obtain the type IIB description of the fractional brane, which now corresponds to D3-brane with one of its world-volume directions wrapped around the circle.

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arXiv2001

Quantum M^2 -> 2Lambda/3 discontinuity for massive gravity with a Lambda term

In a previous paper we showed that the absence of the van Dam-Veltman-Zakharov discontinuity as M^2 -> 0 for massive spin-2 with a Lambda term is an artifact of the tree approximation, and that the discontinuity reappears at one loop, as a result of going from five degrees of freedom to two. In this paper we show that a similar classical continuity but quantum discontinuity arises in the "partially massless" limit M^2 -> 2Lambda/3, as a result of going from five degrees of freedom to four.

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arXiv2001

Hodge Duality on the Brane

It has been claimed that whereas scalars can be bound to a Randall-Sundrum brane, higher p-form potentials cannot, in contradiction with the Hodge duality between 0-form and 3-form potentials in the five-dimensional bulk. Here we show that a 3-form in the bulk correctly yields a 2-form on the brane, in complete agreement with both bulk and brane duality. We also emphasize that the phenomenon of photon screening in the Randall-Sundrum geometry is ruled out by the bulk Einstein equation.

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arXiv2001

Localization of supergravity on the brane

A supersymmetric Randall-Sundrum brane-world demands that not merely the graviton but the entire supergravity multiplet be trapped on the brane. To demonstrate this, we present a complete ansatz for the reduction of (D=5,N=4) gauged supergravity to (D=4,N=2) ungauged supergravity in the Randall-Sundrum geometry. We verify that it is consistent to lowest order in fermion terms. In particular, we show how the graviphotons avoid the `no photons on the brane' result because they do not originate from Maxwell's equations in D=5 but rather from odd-dimensional self-duality equations. In the case of the fivebrane, the Randall-Sundrum mechanism also provides a new Kaluza-Klein way of obtaining chiral supergravity starting from non-chiral.

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arXiv2000

Randall-Sundrum Brane Tensions

We show that the singular sources in the energy-momentum tensor for the Randall-Sundrum brane world, viewed as a solution of type IIB supergravity, are composed of two elements. One of these is a D3-brane source with tension opposite in sign to the RS tension in five dimensions; the other arises from patching two regions of flat ten-dimensional spacetime. This resolves an apparent discrepancy between supersymmetry and the sign and magnitude of the RS tension.

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arXiv2000

Multi-centered black holes in gauged D=5 supergravity

One of the important consequences of the no-force condition for BPS states is the existence of stable static multi-center solutions, at least in ungauged supergravities. This observation has been at the heart of many developments in brane physics, including the construction of intersecting branes and reduced symmetry D-brane configurations corresponding to the Coulomb branch of the gauge theory. However the search for multi-center solutions to gauged supergravities has proven rather elusive. Because of the background curvature, it appears such solutions cannot be static. Nevertheless even allowing for time dependence, general multi-center solutions to gauged supergravity have yet to be constructed. In this letter we investigate the construction of such solutions for the case of D=5, N=2 gauged supergravity coupled to an arbitrary number of vector multiplets. Formally, we find a family of time dependent multi-center black hole solutions which are easily generalized to the case of AdS supergravities in general dimensions. While these are not true solutions, as they have a complex metric and gauge potential, they may be related to a Wick rotated theory or to a theory where the coupling is taken to be imaginary. These solutions thus provide a partial realization of true multi-center black-holes in gauged supergravities.

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arXiv2000

Breathing mode compactifications and supersymmetry of the brane-world

It has recently been shown that the Randall-Sundrum brane-world may be obtained from an appropriate doubled D3-brane configuration in type IIB theory. This corresponds, in five dimensions, to a sphere compactification of the original IIB theory with a non-trivial breathing mode supporting the brane. In this paper, we shall study the supersymmetry of this reduction to massive five-dimensional supergravity, and derive the effective supersymmetry transformations for the fermionic superpartners to the breathing mode. We also consider the sphere compactifications of eleven-dimensional supergravity to both four and seven dimensions. For the compactifications on S^5 and S^7, we include a squashing mode scalar and discuss the truncation from N=8 to N=2 supersymmetry.

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