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Chethan Krishnan

Publications and source records attributed to Chethan Krishnan.

At least 109 records · Page 6Linked to original sources
arXiv2010

Black Hole Vacua and Rotation

Recent developments suggest that the near-region of rotating black holes behaves like a CFT. To understand this better, I propose to study quantum fields in this region. An instructive approach for this might be to put a large black hole in AdS and to think of the entire geometry as a toy model for the ``near-region". Quantum field theory on rotating black holes in AdS can be well-defined (unlike in flat space), if fields are quantized in the co-rotating-with-the-horizon frame. First, some generalities of constructing Hartle-Hawking Green functions in this approach are discussed. Then as a specific example where the details are easy to handle, I turn to 2+1 dimensions (BTZ), write down the Green functions explicitly starting with the co-rotating frame, and observe some structural similarities they have with the Kerr-CFT scattering amplitudes. Finally, in BTZ, there is also an alternate construction for the Green functions: we can start from the covering AdS_3 space and use the method of images. Using a 19th century integral formula, I show the equality between the boundary correlators arising via the two constructions.

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arXiv2009

The Black Di-Ring: An Inverse Scattering Construction

We use the inverse scattering method (ISM) to derive concentric non-supersymmetric black rings. The approach used here is fully five-dimensional, and has the modest advantage that it generalizes readily to the construction of more general axi-symmetric solutions.

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arXiv2009

Generalized BIons in M-theory

In string theory, stacks of D1-branes can expand into intersecting D3-branes. These configurations are called (generalized) BIons. We show how the analogous constructions in M-theory, where M2-branes blow up into calibrated intersections of M5-branes, arise from some of the membrane theories.

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arXiv2009

AdS4/CFT3 at One Loop

I consider semi-classical type IIA strings rotating in the AdS4 part of AdS4 X CP3. The one loop sigma model corrections to this classical solution are used to compute the energy shift, and the result is found to be E-S=f(lambda) ln S with f(lambda)= sqrt{2 lambda} - 5 ln 2 /2 pi + O (1/sqrt{lambda}). Even though the functional forms match, the actual numerical value of this one loop string result differs from the result obtained on the integrable N=6 Chern-Simons (ABJM) theory side.

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arXiv2009

M2-brane Flows and the Chern-Simons Level

The Chern-Simons level k of ABJM gauge theory captures the orbifolding in the dual geometry. This suggests that if we move the membranes away from the tip of the orbifold to a smooth point, it should trigger an RG flow that changes the level to k=1 in the IR. We construct an explicit supergravity solution that is dual to this shift from generic k to k=1. In the gauge theory side, we present arguments for why this shift is plausible at the end of the RG flow. We also consider a resolution of the orbifold for the case k=4 (where explicit metrics can be found), and construct the smooth supergravity solution that interpolates between AdS4 X S7/Z4 and AdS4 X S7, corresponding to localized branes on the blown up six cycle. In the gauge theory, we make some comments about the dimension four operator dual to the resolution as well as the associated RG flow.

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arXiv2009

Tomograms of Spinning Black Holes

The classical internal structure of spinning black holes is vastly different from that of static black holes. We consider spinning BTZ black holes, and probe their interior from the gauge theory. Utilizing the simplicity of the geometry and reverse engineering from the geodesics, we propose a thermal correlator construction which can be interpreted as arising from two entangled CFTs. By analytic continuation of these correlators, we can probe the Cauchy horizon. Correlators that capture the Cauchy horizon in our work have a structure closely related to those that capture the singularity in a non-rotating BTZ. As expected, the regions beyond the Cauchy horizon are not probed in this picture, protecting cosmic censorship.

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arXiv2009

A Comment on Kerr-CFT and Wald Entropy

We point out that the entropies of black holes in general diffeomorphism invariant theories, computed using the Kerr-CFT correspondence and the Wald formula (as implemented in the entropy function formalism), need not always agree. A simple way to illustrate this is to consider Einstein-Gauss-Bonnet gravity in four dimensions, where the Gauss-Bonnet term is topological. This means that the central charge of Kerr-CFT computed in the Barnich-Brandt-Compere formalism remains the same as in Einstein gravity, while the entropy computed using the entropy function gives a universal correction proportional to the Gauss-Bonnet coupling. We argue that at least in this example, the Kerr-CFT result is the physically reasonable one. The resolution to this discrepancy might lie in a better understanding of boundary terms.

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arXiv2009

Membranes, Strings and Integrability

In the first half of this note, after briefly motivating and reviewing membrane field theories, we consider their BPS funnel solutions. We discuss some aspects of embedding M-theory fuzzy funnels in these theories. In the second half, we focus on ABJM theory and explain a test of AdS4/CFT3 based on integrability. We discuss a numerical mismatch at one loop in worldsheet perturbation theory and its possible resolutions.

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arXiv2008

Baryon Dissociation in a Strongly Coupled Plasma

Using the dual string theory, we study a circular baryonic configuration in a wind of strongly coupled N=4 Yang-Mills plasma blowing in the plane of the baryon, before and after a quark has dissociated from it. A simple enough model that captures many interesting features is when there are four quarks in the baryon. As a step towards phenomenology, we compare representative dissociated configurations, and make some comments about their energetics and other properties. Related results that we find include the observation that the screening length formula L_s T ~ (1-v^2)^{1/4} obtained previously for other color singlet configurations, is robust for circular baryons as well.

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arXiv2008

Metastable Black Saturns

Black Saturns have multiple horizons and so offer a testing ground for the ideas of black hole thermodynamics. In this note, we numerically scan for phases that are in equilibrium by extremizing total entropy in the 2-dimensional moduli space of stationary, singly rotating black Saturns with fixed total mass and angular momentum. On top of the known T_H=T_R, Omega_H=Omega_R configurations, we find phases that do not balance the temperature and angular velocity of the ring and the hole. But these (and most of the balanced Saturns) go away when we demand that the system is metastable, by imposing that the Hessian of the entropy is negative definite. Metastablity occurs when the dimensionless total angular momentum lies in a narrow window 0.92457<j<0.92463 of the thin ring branch. This is consistent with the expected range of classical stability of black Saturns and therefore may imply that thermal stability is tied to classical stability, in analogy with Gubser-Mitra in the translationally-invariant case. We also comment on the possibility of constructing plasma configurations that are dual to black Saturns in AdS.

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arXiv2008

Membranes on Calibrations

M2-branes can blow up into BPS funnels that end on calibrated intersections of M5-branes. In this quick note, we make the observation that the constraints required for the consistency of these solutions are automatic in Bagger-Lambert-Gustavsson (BLG) theory, thanks to the fundamental identity and the supersymmetry of the calibration. We use this to explain how the previous ad hoc fuzzy funnel constructions emerge in this picture, and make some comments about the role of the 3-algebra trace form in the derivation.

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arXiv2008

The Mesonic Branch of the Deformed Conifold

Using coordinates that manifest the S^2-S^3 split of the base, we study D3-branes localized on the three-sphere in the Klebanov-Strassler background. We find a numerical solution for the warp factor and show the emergence of the AdS throat near the stack. In the dual gauge theory, this corresponds to an RG flow along the mesonic branch. We demonstrate how the cubic superpotential of the N=4 SYM theory emerges at the end of the RG flow.

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arXiv2008

Vacuum Bubble in an Inhomogeneous Cosmology

We study the propagation of bubbles of new vacuum in a radially inhomogeneous Lemaitre-Tolman-Bondi background that includes a cosmological constant. This exemplifies the classical evolution of a tunneling bubble through a metastable state with curvature inhomogeneities, and will be relevant in the context of the Landscape. We demand that the matter profile in the LTB background satisfy the weak energy condition. For sample profiles that satisfy this restriction, we find that the evolution of the bubble (in terms of the physically relevant coordinates intrinsic to the shell) is largely unaffected by the prsence of local inhomogeneities. Our setup should also be a useful toy model for capturing the effects of ambient inhomogeneities on an inflating region.

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arXiv2008

Gauge Theory RG Flows from a Warped Resolved Orbifold

We study gauge-string duality of D3-branes localized at a point on the resolution of the ALE orbifold $\IC^3/\IZ_3$. By explicitly solving for the warp factor, we demonstrate the holographic RG flow from $AdS_5 \times S^5/\IZ_3$ (far away from the resolution) to the usual $AdS_5\times S^5$ (close to the stack). On the gauge theory side, this maps to the flow between the quiver gauge theory and ${\cal N}=4$ super Yang-Mills. We present two possible scenarios for this RG flow depending on the choice of the VEVs. In particular, one of the scenarios proceeds by two steps involving both Higgsing and confinement.

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arXiv2007

Can Quantum de Sitter Space Have Finite Entropy?

If one tries to view de Sitter as a true (as opposed to a meta-stable) vacuum, there is a tension between the finiteness of its entropy and the infinite-dimensionality of its Hilbert space. We invetsigate the viability of one proposal to reconcile this tension using $q$-deformation. After defining a differential geometry on the quantum de Sitter space, we try to constrain the value of the deformation parameter by imposing the condition that in the undeformed limit, we want the real form of the (inherently complex) quantum group to reduce to the usual SO(4,1) of de Sitter. We find that this forces $q$ to be a real number. Since it is known that quantum groups have finite-dimensional representations only for $q=$ root of unity, this suggests that standard $q$-deformations cannot give rise to finite dimensional Hilbert spaces, ruling out finite entropy for q-deformed de Sitter.

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arXiv2007

An Invitation to String Theory

It is hoped that these lectures will give a point of entry into that vast web of related ideas that go under the name "string theory". I start with a more or less qualitative introduction to gravity as a field theory and sketch how one might try to quantize it. Quantizing gravity using the usual techniques of field theory will turn out to be unsuccessful, and that will be a motivation for trying an indirect approach: string theory. I present bosonic string theory, quantize the closed string in the light cone gauge and show that one of the states in the closed string Hilbert space can be interpreted as a graviton. I will end with some general qualitative ideas on slightly more advanced topics.

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arXiv2007

Cascading Quivers from Decaying D-branes

We use an argument analogous to that of Kachru, Pearson and Verlinde to argue that cascades in L^{a,b,c} quiver gauge theories always preserve the form of the quiver, and that all gauge groups drop at each step by the number M of fractional branes. In particular, we demonstrate that an NS5-brane that sweeps out the S^3 of the base of L^{a,b,c} destroys M D3-branes.

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