Borun Chowdhury - Academia.edu (original) (raw)

Uploads

Papers by Borun Chowdhury

It is possible to construct a special family of nonextremal black hole microstates. These microst... more It is possible to construct a special family of nonextremal black hole microstates. These microstates are unstable, and emit radiation at a rate which is found to exactly equal the Hawking radiation rate predicted for them by the dual CFT. In this paper we analyze in more detail the nature of the radiation created by these unstable modes. The energy and angular momentum of the mode is found to be localized in two regions: one near infinity corresponding to the emitted quanta, and the other in the ergoregion which is deep inside the interior of the geometry. The energy and angular momenta are equal and opposite for these two contributions, as expected for emission from ergoregions. We conjecture that more general nonextremal microstates will possess ergoregions (with no axial symmetry), and radiation from these regions can be part of the general Hawking emission for the microstates.

We compute the gravitational entropy of “spherical Rindler space”, a time-dependent, spherically ... more We compute the gravitational entropy of “spherical Rindler space”, a time-dependent, spherically symmetric generalization of ordinary Rindler space, defined with reference to a family of observers traveling along non-parallel, accelerated trajectories. All these observers are causally disconnected from a spherical region H (a “hole”) located at the origin of Minkowski space. The entropy evaluates to S = A/4G, where A is the area of the spherical acceleration horizon, which coincides with the boundary of H. We propose that S is the entropy of entanglement between quantum gravitational degrees of freedom supporting the interior and the exterior of the sphere H.

Abstract: It is generally believed that the eternal AdS black hole is dual to two confor-mal fiel... more Abstract: It is generally believed that the eternal AdS black hole is dual to two confor-mal field theories with compact spatial sections that are together in a thermofield double state. We argue that this proposal is incorrect, and by extension so are the “entangle-ment=geometry ” proposal of Van Raamsdonk and “ER=EPR ” proposal of Maldacena and Susskind. We show that in the bulk there is an interaction needed between the two halves of the Hilbert space for connectivity across the horizon; however, there is no such interaction between the CFTs. This rules out the possibility of the dual to the CFTs being the eternal AdS black hole. We argue the correct dual “geometries ” resemble the exterior of the black hole outside the stretched horizon but cap off before the global horizon. This disallows the possibility of a shared future (and past) wedge where Alice falling from one side can meet Bob falling from the other. We expect that in the UV complete theory the aforementioned caps will...

Abstract: We study the fate of two-centered D1-D5 systems on T 4 away from the singular supergrav... more Abstract: We study the fate of two-centered D1-D5 systems on T 4 away from the singular supergravity point in the moduli space. We do this by considering a background D1-D5 black hole with a self-dual B-field moduli turned on and treating the second center in the probe limit in this background. We find that in general marginal bound states at zero moduli become metastable at finite B-moduli, demonstrating a breaking of supersymmetry. However, we also find evidence that when the charges of both centers are comparable, the effects of supersymmetry breaking become negligible. We show that this effect is independent of string coupling and thus it should be possible to reproduce this in the CFT at weak coupling. We comment on the implications for the fuzzball proposal.

It is shown that exp(−2 Im ( ∫ p dr)) is not invariant under canonical transformations in general... more It is shown that exp(−2 Im ( ∫ p dr)) is not invariant under canonical transformations in general. Specifically for shells tunneling out of black holes, this quantity is not invariant under canonical transformations. It can be interpreted as the transmission coefficient only in the cases in which it is invariant under canonical transformations. Although such cases include alpha decay, they do not include the tunneling of shells from black holes. The simplest extension to this formula which is invariant under canonical transformations is proposed. However it is shown that this gives half the correct temperature for black holes. 1

[

It is shown that exp(−2 Im ( ∫ p dr)) is not invariant under canonical transformations in general... more It is shown that exp(−2 Im ( ∫ p dr)) is not invariant under canonical transformations in general. Specifically for shells tunneling out of black holes, this quantity is not invariant under canonical transformations. It can be interpreted as the tunneling probability only in the cases in which it is invariant under canonical transformations. Although such cases include alpha decay, they do not include the tunneling of shells from black holes. This demonstrates that this naive expression for tunneling probability does not hold for the case of shells tunneling out of black holes.

It is shown that in general the quantity exp(−2Im ( ∫ p dr)) is not invariant under canonical tra... more It is shown that in general the quantity exp(−2Im ( ∫ p dr)) is not invariant under canonical transformations. It can be interpreted as the tunneling probability only in specific cases which include the text book example of alpha decay but do not include a shell crossing a black hole horizon. With specific examples it is shown that this quantity is different for different canonically equivalent actions thus demonstrating that its interpretation as tunneling probability for black hole emission is questionable.

arXiv: High Energy Physics - Theory, 2013

It is generally believed that the eternal AdS black hole is dual to two conformal field theories ... more It is generally believed that the eternal AdS black hole is dual to two conformal field theories with compact spatial sections that are together in a thermofield double state. We argue that this proposal is incorrect, and by extension so are the "entanglement=geometry" proposal of Van Raamsdonk and "ER=EPR" proposal of Maldacena and Susskind. We show that in the bulk there is an interaction needed between the two halves of the Hilbert space for connectivity across the horizon; however, there is no such interaction between the CFTs. This rules out the possibility of the dual to the CFTs being the eternal AdS black hole. We argue the correct dual "geometries" resemble the exterior of the black hole outside the stretched horizon but cap off before the global horizon. This disallows the possibility of a shared future (and past) wedge where Alice falling from one side can meet Bob falling from the other. We expect that in the UV complete theory the aforement...

These lecture notes present an introduction to the fuzzball proposal and emission from the D1-D5 ... more These lecture notes present an introduction to the fuzzball proposal and emission from the D1-D5 system which is geared to an audience of graduate students and others with little background in the subject. The presentation begins with a discussion of the Penrose process and Hawking radiation. The fuzzball proposal is then introduced, and the twoand three-charge systems are reviewed. In the three-charge case details are not discussed. A detailed discussion of emission calculations for D1-D5-P black holes and for certain nonextremal fuzzballs from both the gravity and CFT perspectives is included. We explicitly demonstrate how seemingly different emission processes in gravity, namely, Hawking radiation and superradiance from D1-D5-P black holes, and ergoregion emission from certain non-extremal fuzzballs, are only different manifestations of the same phenomenon in the CFT.

Monthly Notices of the Royal Astronomical Society

We embed spherical Rindler space -- a geometry with a spherical hole in its center -- in asymptot... more We embed spherical Rindler space -- a geometry with a spherical hole in its center -- in asymptotically AdS spacetime and show that it carries a gravitational entropy proportional to the area of the hole. Spherical AdS-Rindler space is holographically dual to an ultraviolet sector of the boundary field theory given by restriction to a strip of finite duration in time. Because measurements have finite durations, local observers in the field theory can only access information about bounded spatial regions. We propose a notion of Residual Entropy that captures uncertainty about the state of a system left by the collection of local, finite-time observables. For two-dimensional conformal field theories we use holography and the strong subadditivity of entanglement to propose a formula for Residual Entropy and show that it precisely reproduces the areas of circular holes in AdS3. Extending the notion to field theories on strips with variable durations in time, we show more generally that ...

It is generally believed that the eternal AdS black hole is dual to two conformal field theories ... more It is generally believed that the eternal AdS black hole is dual to two conformal field theories with compact spatial sections that are together in a thermofield double state. We argue that this proposal is incorrect, and by extension so are the "entanglement=geometry" proposal of Van Raamsdonk and "ER=EPR" proposal of Maldacena and Susskind. We show that in the bulk there is an interaction needed between the two halves of the Hilbert space for connectivity across the horizon; however, there is no such interaction between the CFTs. This rules out the possibility of the dual to the CFTs being the eternal AdS black hole. We argue the correct dual "geometries" resemble the exterior of the black hole outside the stretched horizon but cap off before the global horizon. This disallows the possibility of a shared future (and past) wedge where Alice falling from one side can meet Bob falling from the other. We expect that in the UV complete theory the aforement...

In the AdS/CFT correspondence, CFTs are identified by asymptotic boundary surfaces and the bounda... more In the AdS/CFT correspondence, CFTs are identified by asymptotic boundary surfaces and the boundary conditions imposed on those surfaces. However, AdS can be foliated in various ways to give different boundaries. We show that the CFTs obtained using certain distinct foliations are different. This difference arises because the asymptotic region of a foliation overlaps with the deep interior region of another. In particular we focus on the CFTs defined on surfaces of large constant radius in global coordinates, Rindler-AdS coordinates, and Poincar\'e coordinates for AdS$_3$. We refer to these as global-CFT, Rindler-CFT and Poincar\'e-CFT respectively. We demonstrate that the correlators for these CFTs are different and argue that the bulk duals to these should agree up to very close to the respective horizons but then start differing. Since the BTZ black hole is obtained as a quotient of AdS$_3$, we discuss the implications of our results for bulk duals of periodically-identif...

A simple classical consideration of black hole formation and evaporation times as measured by an ... more A simple classical consideration of black hole formation and evaporation times as measured by an observer at infinity demonstrates that an infall cutoff outside the event horizon of a black hole must be imposed in order for the formation time of a black hole event horizon to not exceed its evaporation time. We explore this paradox quantitatively and examine possible cutoff scales and their relation to the Planck scale. Our analysis suggests several different possibilities, none of which can be resolved classically and all of which require new physics associated with even large black holes and macroscopic event horizons:(1) an event horizon never forms, for example due to radiation during collapse (resolving the information loss problem), (2) and/or quantum effects may affect space-time near an event horizon in ways which alter infall as well as black hole evaporation itself.

Journal of High Energy Physics, 2012

Journal of High Energy Physics, 2015

International Journal of Modern Physics D, 2013

In this paper, we examine the implications of the ongoing black holes versus firewalls debate for... more In this paper, we examine the implications of the ongoing black holes versus firewalls debate for the thermo-field dynamics of black holes by analyzing a conformal field theory (CFT) in a thermal state in the context of anti-de Sitter/CFT. We argue that the thermo-field doubled copy of the thermal CFT should be thought of not as a fictitious system, but as the image of the CFT in the heat bath. In case of strong coupling between the CFT and the heat bath, this image allows for free infall through the horizon and the system is described by a black hole. Conversely, firewalls are the appropriate dual description in case of weak interaction of the CFT with its heat bath.

It is possible to construct a special family of nonextremal black hole microstates. These microst... more It is possible to construct a special family of nonextremal black hole microstates. These microstates are unstable, and emit radiation at a rate which is found to exactly equal the Hawking radiation rate predicted for them by the dual CFT. In this paper we analyze in more detail the nature of the radiation created by these unstable modes. The energy and angular momentum of the mode is found to be localized in two regions: one near infinity corresponding to the emitted quanta, and the other in the ergoregion which is deep inside the interior of the geometry. The energy and angular momenta are equal and opposite for these two contributions, as expected for emission from ergoregions. We conjecture that more general nonextremal microstates will possess ergoregions (with no axial symmetry), and radiation from these regions can be part of the general Hawking emission for the microstates.

We compute the gravitational entropy of “spherical Rindler space”, a time-dependent, spherically ... more We compute the gravitational entropy of “spherical Rindler space”, a time-dependent, spherically symmetric generalization of ordinary Rindler space, defined with reference to a family of observers traveling along non-parallel, accelerated trajectories. All these observers are causally disconnected from a spherical region H (a “hole”) located at the origin of Minkowski space. The entropy evaluates to S = A/4G, where A is the area of the spherical acceleration horizon, which coincides with the boundary of H. We propose that S is the entropy of entanglement between quantum gravitational degrees of freedom supporting the interior and the exterior of the sphere H.

Abstract: It is generally believed that the eternal AdS black hole is dual to two confor-mal fiel... more Abstract: It is generally believed that the eternal AdS black hole is dual to two confor-mal field theories with compact spatial sections that are together in a thermofield double state. We argue that this proposal is incorrect, and by extension so are the “entangle-ment=geometry ” proposal of Van Raamsdonk and “ER=EPR ” proposal of Maldacena and Susskind. We show that in the bulk there is an interaction needed between the two halves of the Hilbert space for connectivity across the horizon; however, there is no such interaction between the CFTs. This rules out the possibility of the dual to the CFTs being the eternal AdS black hole. We argue the correct dual “geometries ” resemble the exterior of the black hole outside the stretched horizon but cap off before the global horizon. This disallows the possibility of a shared future (and past) wedge where Alice falling from one side can meet Bob falling from the other. We expect that in the UV complete theory the aforementioned caps will...

Abstract: We study the fate of two-centered D1-D5 systems on T 4 away from the singular supergrav... more Abstract: We study the fate of two-centered D1-D5 systems on T 4 away from the singular supergravity point in the moduli space. We do this by considering a background D1-D5 black hole with a self-dual B-field moduli turned on and treating the second center in the probe limit in this background. We find that in general marginal bound states at zero moduli become metastable at finite B-moduli, demonstrating a breaking of supersymmetry. However, we also find evidence that when the charges of both centers are comparable, the effects of supersymmetry breaking become negligible. We show that this effect is independent of string coupling and thus it should be possible to reproduce this in the CFT at weak coupling. We comment on the implications for the fuzzball proposal.

It is shown that exp(−2 Im ( ∫ p dr)) is not invariant under canonical transformations in general... more It is shown that exp(−2 Im ( ∫ p dr)) is not invariant under canonical transformations in general. Specifically for shells tunneling out of black holes, this quantity is not invariant under canonical transformations. It can be interpreted as the transmission coefficient only in the cases in which it is invariant under canonical transformations. Although such cases include alpha decay, they do not include the tunneling of shells from black holes. The simplest extension to this formula which is invariant under canonical transformations is proposed. However it is shown that this gives half the correct temperature for black holes. 1

[

It is shown that exp(−2 Im ( ∫ p dr)) is not invariant under canonical transformations in general... more It is shown that exp(−2 Im ( ∫ p dr)) is not invariant under canonical transformations in general. Specifically for shells tunneling out of black holes, this quantity is not invariant under canonical transformations. It can be interpreted as the tunneling probability only in the cases in which it is invariant under canonical transformations. Although such cases include alpha decay, they do not include the tunneling of shells from black holes. This demonstrates that this naive expression for tunneling probability does not hold for the case of shells tunneling out of black holes.

It is shown that in general the quantity exp(−2Im ( ∫ p dr)) is not invariant under canonical tra... more It is shown that in general the quantity exp(−2Im ( ∫ p dr)) is not invariant under canonical transformations. It can be interpreted as the tunneling probability only in specific cases which include the text book example of alpha decay but do not include a shell crossing a black hole horizon. With specific examples it is shown that this quantity is different for different canonically equivalent actions thus demonstrating that its interpretation as tunneling probability for black hole emission is questionable.

arXiv: High Energy Physics - Theory, 2013

It is generally believed that the eternal AdS black hole is dual to two conformal field theories ... more It is generally believed that the eternal AdS black hole is dual to two conformal field theories with compact spatial sections that are together in a thermofield double state. We argue that this proposal is incorrect, and by extension so are the "entanglement=geometry" proposal of Van Raamsdonk and "ER=EPR" proposal of Maldacena and Susskind. We show that in the bulk there is an interaction needed between the two halves of the Hilbert space for connectivity across the horizon; however, there is no such interaction between the CFTs. This rules out the possibility of the dual to the CFTs being the eternal AdS black hole. We argue the correct dual "geometries" resemble the exterior of the black hole outside the stretched horizon but cap off before the global horizon. This disallows the possibility of a shared future (and past) wedge where Alice falling from one side can meet Bob falling from the other. We expect that in the UV complete theory the aforement...

These lecture notes present an introduction to the fuzzball proposal and emission from the D1-D5 ... more These lecture notes present an introduction to the fuzzball proposal and emission from the D1-D5 system which is geared to an audience of graduate students and others with little background in the subject. The presentation begins with a discussion of the Penrose process and Hawking radiation. The fuzzball proposal is then introduced, and the twoand three-charge systems are reviewed. In the three-charge case details are not discussed. A detailed discussion of emission calculations for D1-D5-P black holes and for certain nonextremal fuzzballs from both the gravity and CFT perspectives is included. We explicitly demonstrate how seemingly different emission processes in gravity, namely, Hawking radiation and superradiance from D1-D5-P black holes, and ergoregion emission from certain non-extremal fuzzballs, are only different manifestations of the same phenomenon in the CFT.

Monthly Notices of the Royal Astronomical Society

We embed spherical Rindler space -- a geometry with a spherical hole in its center -- in asymptot... more We embed spherical Rindler space -- a geometry with a spherical hole in its center -- in asymptotically AdS spacetime and show that it carries a gravitational entropy proportional to the area of the hole. Spherical AdS-Rindler space is holographically dual to an ultraviolet sector of the boundary field theory given by restriction to a strip of finite duration in time. Because measurements have finite durations, local observers in the field theory can only access information about bounded spatial regions. We propose a notion of Residual Entropy that captures uncertainty about the state of a system left by the collection of local, finite-time observables. For two-dimensional conformal field theories we use holography and the strong subadditivity of entanglement to propose a formula for Residual Entropy and show that it precisely reproduces the areas of circular holes in AdS3. Extending the notion to field theories on strips with variable durations in time, we show more generally that ...

It is generally believed that the eternal AdS black hole is dual to two conformal field theories ... more It is generally believed that the eternal AdS black hole is dual to two conformal field theories with compact spatial sections that are together in a thermofield double state. We argue that this proposal is incorrect, and by extension so are the "entanglement=geometry" proposal of Van Raamsdonk and "ER=EPR" proposal of Maldacena and Susskind. We show that in the bulk there is an interaction needed between the two halves of the Hilbert space for connectivity across the horizon; however, there is no such interaction between the CFTs. This rules out the possibility of the dual to the CFTs being the eternal AdS black hole. We argue the correct dual "geometries" resemble the exterior of the black hole outside the stretched horizon but cap off before the global horizon. This disallows the possibility of a shared future (and past) wedge where Alice falling from one side can meet Bob falling from the other. We expect that in the UV complete theory the aforement...

In the AdS/CFT correspondence, CFTs are identified by asymptotic boundary surfaces and the bounda... more In the AdS/CFT correspondence, CFTs are identified by asymptotic boundary surfaces and the boundary conditions imposed on those surfaces. However, AdS can be foliated in various ways to give different boundaries. We show that the CFTs obtained using certain distinct foliations are different. This difference arises because the asymptotic region of a foliation overlaps with the deep interior region of another. In particular we focus on the CFTs defined on surfaces of large constant radius in global coordinates, Rindler-AdS coordinates, and Poincar\'e coordinates for AdS$_3$. We refer to these as global-CFT, Rindler-CFT and Poincar\'e-CFT respectively. We demonstrate that the correlators for these CFTs are different and argue that the bulk duals to these should agree up to very close to the respective horizons but then start differing. Since the BTZ black hole is obtained as a quotient of AdS$_3$, we discuss the implications of our results for bulk duals of periodically-identif...

A simple classical consideration of black hole formation and evaporation times as measured by an ... more A simple classical consideration of black hole formation and evaporation times as measured by an observer at infinity demonstrates that an infall cutoff outside the event horizon of a black hole must be imposed in order for the formation time of a black hole event horizon to not exceed its evaporation time. We explore this paradox quantitatively and examine possible cutoff scales and their relation to the Planck scale. Our analysis suggests several different possibilities, none of which can be resolved classically and all of which require new physics associated with even large black holes and macroscopic event horizons:(1) an event horizon never forms, for example due to radiation during collapse (resolving the information loss problem), (2) and/or quantum effects may affect space-time near an event horizon in ways which alter infall as well as black hole evaporation itself.

Journal of High Energy Physics, 2012

Journal of High Energy Physics, 2015

International Journal of Modern Physics D, 2013

In this paper, we examine the implications of the ongoing black holes versus firewalls debate for... more In this paper, we examine the implications of the ongoing black holes versus firewalls debate for the thermo-field dynamics of black holes by analyzing a conformal field theory (CFT) in a thermal state in the context of anti-de Sitter/CFT. We argue that the thermo-field doubled copy of the thermal CFT should be thought of not as a fictitious system, but as the image of the CFT in the heat bath. In case of strong coupling between the CFT and the heat bath, this image allows for free infall through the horizon and the system is described by a black hole. Conversely, firewalls are the appropriate dual description in case of weak interaction of the CFT with its heat bath.