arXiv subjects

Ibrahima Bah

Publications and source records attributed to Ibrahima Bah.

At least 55 records · Page 3Linked to original sources

arXiv2019

Black holes, gravitational waves and fundamental physics: a roadmap

The grand challenges of contemporary fundamental physics---dark matter, dark energy, vacuum energy, inflation and early universe cosmology, singularities and the hierarchy problem---all involve gravity as a key component. And of all gravitational phenomena, black holes stand out in their elegant simplicity, while harbouring some of the most remarkable predictions of General Relativity: event horizons, singularities and ergoregions. The hitherto invisible landscape of the gravitational Universe is being unveiled before our eyes: the historical direct detection of gravitational waves by the LIGO-Virgo collaboration marks the dawn of a new era of scientific exploration. Gravitational-wave astronomy will allow us to test models of black hole formation, growth and evolution, as well as models of gravitational-wave generation and propagation. It will provide evidence for event horizons and ergoregions, test the theory of General Relativity itself, and may reveal the existence of new fundamental fields. The synthesis of these results has the potential to radically reshape our understanding of the cosmos and of the laws of Nature. The purpose of this work is to present a concise, yet comprehensive overview of the state of the art in the relevant fields of research, summarize important open problems, and lay out a roadmap for future progress.

gr-qc↗

arXiv2018

Holographic duals of five-dimensional SCFTs on a Riemann surface

We study the twisted compactifications of five-dimensional Seiberg SCFTs, with $SU_\mathcal{M}(2)\times E_{N_f+1}$ flavor symmetry, on a generic Riemann surface that preserves four supercharges. The five-dimensional SCFTs are obtained from the decoupling limit of $N$ D4-branes probing a geometry of $N_f<8$ D8-branes and an O8-plane. In addition to the R-symmetry, we can also twist the flavor symmetry by turning on background flux on the Riemann surface. In particular, in the string theory construction of the five-dimensional SCFTs, the background flux for the $SU_\mathcal{M}(2)$ has a geometric origin, similar to the topological twist of the R-symmetry. We argue that the resulting low-energy three-dimensional theories describe the dynamics on the world-volume of the $N$ D4-branes wrapped on the Riemann surface in the O8/D8 background. The Riemann surface can be described as a curve in a Calabi-Yau three-fold that is a sum of two line bundles over it. This allows for an explicit construction of $AdS_4$ solutions in massive IIA supergravity dual to the world-volume theories, thereby providing strong evidence that the three-dimensional SCFTs exist in the low-energy limit of the compactification of the five-dimensional SCFTs. We compute observables such as the free energy and the scaling dimensions of operators dual to D2-brane probes; these have non-trivial dependence on the twist parameter for the $U(1)$ in $SU_\mathcal{M}(2)$. The free energy exhibits the $N^{5/2}$ scaling that is emblematic of five-dimensional SCFTs.

hep-th↗

arXiv2018

Structure of Anomalies of 4d SCFTs from M5-branes, and Anomaly Inflow

We study the 't Hooft anomalies of four-dimensional superconformal field theories that arise from M5-branes wrapped on a punctured Riemann surface. In general there are two independent contributions to the anomalies. There is a bulk term obtained by integrating the anomaly polynomial of the world-volume theory on the M5-branes over the Riemann surface; this contribution knows about the punctures only through its dependence on the Euler characteristic of the surface. The second set of contributions comes from local data at the punctures; these terms are independent from the bulk data of the surface. Using anomaly inflow in M-theory, we describe the general structure of the anomalies for cases when the four-dimensional theories preserve N=2 supersymmetry. We additionally discuss the anomalies corresponding to (p,q) punctures in N=1 theories.

hep-th↗

arXiv2018

Class $\mathcal{S}$ Anomalies from M-theory Inflow

We present a first principles derivation of the anomaly polynomials of 4d $\mathcal{N} = 2$ class $\mathcal{S}$ theories of type $A_{N-1}$ with arbitrary regular punctures, using anomaly inflow in the corresponding M-theory setup with $N$ M5-branes wrapping a punctured Riemann surface. The labeling of punctures in our approach follows entirely from the analysis of the 11d geometry and $G_4$ flux. We highlight the applications of the inflow method to the AdS/CFT correspondence.

hep-th↗

arXiv2018

4d N=1 from 6d N=(1,0) on a torus with fluxes

Compactifying N=(1,0) theories on a torus, with additional fluxes for global symmetries, we obtain N=1 supersymmetric theories in four dimensions. It is shown that for many choices of flux these models are toric quiver gauge theories with singlet fields. In particular we compare the anomalies deduced from the description of the six-dimensional theory and the anomalies of the quiver gauge theories. We also give predictions for anomalies of four-dimensional theories corresponding to general compactifications of M5-branes probing C_2/Z_k singularities.

hep-th↗

arXiv2017

AdS5 compactifications with punctures in massive IIA supergravity

We find AdS5 solutions holographically dual to compactifications of six-dimensional N=(1,0) supersymmetric field theories on Riemann surfaces with punctures. We simplify a previous analysis of supersymmetric AdS5 IIA solutions, and with a suitable Ansatz we find explicit solutions organized in three classes, where an O8--D8 stack, D6- and D4-branes are simultaneously present, localized and partially localized. The D4-branes are smeared over the Riemann surface and this is interpreted as the presence of a uniform distribution of punctures. For the first class we identify the corresponding six-dimensional theory as an E-string theory coupled to a quiver gauge theory. The second class of solutions lacks D6-branes and its central charge scales as $n^{5/2}$, suggesting a five-dimensional origin for the dual field theory. The last class has elements of the previous two.

hep-th↗

arXiv2015

Gravity duals of N=(0,2) SCFTs from M5-branes

We describe the general BPS system that governs the gravity duals of N=(0,2) two-dimensional superconformal field theories in the low-energy limit of M5-branes on a four-manifold, M4. In order to preserve supersymmetry, we restrict to cases where the four-manifold is embedded in a Calabi-Yau fourfold that is a sum of two line bundles over M4. We further reduce the N=(0,2) system to describe the gravity duals of SCFTs with N=(0,4) and N=(2,2) supersymmetry. In the first case, the solutions fit in the larger class of AdS3xS2xCY3 solutions of M-theory dual to N=(0,4) SCFTs. In the case of the N=(2,2) theories, the near-horizon limit of M4 is necessarily a product of two constant curvature Riemann surfaces whose metrics are governed by a pair of Liouville equations.

hep-th↗

arXiv2015

Quiver Tails and N=1 SCFTs from M5-branes

We study a class of four-dimensional N=1 superconformal field theories obtained by wrapping M5-branes on a Riemann surface with punctures. We identify UV descriptions of four-dimensional SCFTs corresponding to curves with a class of punctures. The quiver tails appearing in these UV descriptions differ significantly from their N=2 counterpart. We find a new type of object that we call the `Fan'. We show how to construct new N=1 superconformal theories using the Fan. Various dual descriptions for these SCFTs can be identified with different colored pair-of-pants decompositions. For example, we find an N=1 analog of Argyres-Seiberg duality for the SU(N) SQCD with 2N flavors. We also compute anomaly coefficients and superconformal indices for these theories and show that they are invariant under dualities.

hep-th↗

arXiv2015

AdS5 solutions from M5-branes on Riemann surface and D6-branes sources

We describe the gravity duals of four-dimensional N=1 superconformal field theories obtained by wrapping M5-branes on a punctured Riemann surface. The internal geometry, normal to the AdS5 factor, generically preserves two U(1)s, with generators (J+,J-), that are fibered over the Riemann surface. The metric is governed by a single potential that satisfies a version of the Monge-Ampere equation. The spectrum of N=1 punctures is given by the set of supersymmetric sources of the potential that are localized on the Riemann surface and lead to regular metrics near a puncture. We use this system to study a class of punctures where the geometry near the sources corresponds to M-theory description of D6-branes. These carry a natural (p,q) label associated to the circle dual to the killing vector (p J+ + q J-) which shrinks near the source. In the generic case the world volume of the D6-branes is AdS5 X S^2 and they locally preserve N=2 supersymmetry. When p=-q, the shrinking circle is dual to a flavor U(1). The metric in this case is non-degenerate only when there are co-dimension one sources, M9-branes, obtained by smearing M5-branes that wrap the AdS5 factor and the circle dual the superconformal R-symmetry. In the IIA limit, they can interpreted as D8-branes. The D6-branes are extended along the AdS5 and on cups that end on the co-dimension one branes. In the special case when the shrinking circle is dual to the R-symmetry, the D6-branes are extended along the AdS5 and wrap an auxiliary Riemann surface with an arbitrary genus. When the Riemann surface is compact with constant curvature, the system is governed by a Monge-Ampere equation.

hep-th↗

arXiv2014

BPS M5-branes as Defects for the 3d-3d Correspondence

We study supersymmetric probe M5-branes in the AdS_4 solution that arises from M5-branes wrapped on a hyperbolic 3-manifold M_3. This amounts to introducing internal defects within the framework of the 3d-3d correspondence. The BPS condition for a probe M5-brane extending along all of AdS_4 requires it to wrap a surface embedded in an S^2-fibration over M_3. We find that the projection of this surface to M_3 can be either a geodesic or a tubular surface around a geodesic. These configurations preserve an extra U(1) symmetry, in addition to the one corresponding to the R-symmetry of the dual 3d N=2 gauge theory. BPS M2-branes can stretch between M5-branes wrapping geodesics. We interpret the addition of probe M5-branes on a closed geodesic in terms of conformal Dehn surgery.

hep-th↗

arXiv2013

Punctures from Probe M5-Branes and N=1 Superconformal Field Theories

We study probe M5-branes in N=1 AdS5 solutions of M-theory that arise from M5-branes wrapped on a Riemann surface. Using the BPS condition from kappa-symmetry, we classify supersymmetric probe M5-branes that extend along all of AdS5 and intersect the Riemann surface at points. These can be viewed as punctures in the dual N=1 superconformal field theories. We find M5-branes that correspond to the two types of simple punctures previously studied in field theory. In addition, when the central charge is rational, we find a new class of M5-branes with a moduli space that includes two internal dimensions in addition to the Riemann surface. These new M5-branes have the essential characteristic of fractional branes, in that a single one at a generic point of its moduli space becomes multiple M5-branes at special points.

hep-th↗

arXiv2013

Linear Quivers and N=1 SCFTs from M5-branes

We study a class of N=1 quiver gauge theories build out of vector multiplets and matter multiplets in the fundamental and bifundamental representations. We argue that these theories flow to interacting SCFTs in the IR and calculate their central charges. We exhibit a type IIA brane construction which at low energies is described by these SCFTs. This also leads to a natural description of the theories in terms of M5-branes on a punctured sphere.

hep-th↗

arXiv2013

Quarter-BPS AdS5 solutions in M-theory with a T2 bundle over a Riemann surface

We study and classify quarter-BPS AdS5 systems in M-theory, whose internal six-dimensional geometry is a T2 bundle over a Riemann surface and two interval directions. The general system presented, provides a unified description of all known AdS5 solutions in M-theory. These systems are governed by two functions, one that corresponds to the conformal factor of the Riemann surface and another that describes the T2 fibration. We find solutions that can be organized into two classes. In the first one, solutions are specified by the conformal factor of the Riemann surface which satisfies a warped generalization of the SU(infinity) Toda equation. The system in the second class requires the Riemann surface to be S2, H2 or T2. Class one contains the M-theory AdS5 solutions of Lin, Lunin and Maldacena; the solutions of Maldacena and Nunez; the solutions of Gauntlett, Martelli, Sparks and Waldram; and the eleven-dimensional uplift of the Y(p,q) metrics. The second includes the recently found solutions of Beem, Bobev, Wecht and the author. Within each class there are new solutions that will be studied in a companion paper.

hep-th↗

arXiv2012

AdS/CFT Dual Pairs from M5-Branes on Riemann Surfaces

In this letter we describe an infinite family of new N=1 AdS_5/CFT_4 dual pairs which arise from M5-branes wrapping Riemann surfaces in Calabi-Yau threefolds. We use the relevant brane constructions to compute the central charges of the infrared fixed points from the M5-brane anomaly polynomial. We then present AdS_5 x M_6 solutions of eleven-dimensional supergravity which are dual to these CFTs at large N. Finally, we provide a purely four-dimensional field theory construction which flows to a special class of these fixed points. These theories will be further elaborated upon in a companion paper.

hep-th↗

arXiv2012

Four-Dimensional SCFTs from M5-Branes

We engineer a large new set of four-dimensional N=1 superconformal field theories by wrapping M5-branes on complex curves. We present new supersymmetric AdS_5 M-theory backgrounds which describe these fixed points at large N, and then directly construct the dual four-dimensional CFTs for a certain subset of these solutions. Additionally, we provide a direct check of the central charges of these theories by using the M5-brane anomaly polynomial. This is a companion paper which elaborates upon results reported in arXiv:1112:5487.

hep-th↗

arXiv2011

New N=1 Superconformal Field Theories In Four Dimensions

We construct a large new family of four-dimensional N=1 superconformal field theories by coupling Gaiotto's T_N theories to N=1 vector multiplets. In particular, we consider theories in which various T_N blocks are linked together via bifundamental and adjoint chiral superfields, with no superpotential. We find that while some of these constructions appear to give new strongly coupled SCFTs, others lead to violations of the a-theorem, and thus do not appear to be good interacting theories.

hep-th↗

arXiv2010

Fermions and Type IIB Supergravity On Squashed Sasaki-Einstein Manifolds

We discuss the dimensional reduction of fermionic modes in a recently found class of consistent truncations of type IIB supergravity compactified on squashed five-dimensional Sasaki-Einstein manifolds. We derive the lower dimensional equations of motion and effective action, and comment on the supersymmetry of the resulting theory, which is consistent with N=4 gauged supergravity in $d=5$, coupled to two vector multiplets. We compute fermion masses by linearizing around two $AdS_{5}$ vacua of the theory: one that breaks N=4 down to N=2 spontaneously, and a second one which preserves no supersymmetries. The truncations under consideration are noteworthy in that they retain massive modes which are charged under a U(1) subgroup of the $R$-symmetry, a feature that makes them interesting for applications to condensed matter phenomena via gauge/gravity duality. In this light, as an application of our general results we exhibit the coupling of the fermions to the type IIB holographic superconductor, and find a consistent further truncation of the fermion sector that retains a single spin-1/2 mode.

hep-th↗

arXiv2010

Fermions and D=11 Supergravity On Squashed Sasaki-Einstein Manifolds

We discuss the dimensional reduction of fermionic modes in a recently found class of consistent truncations of D=11 supergravity compactified on squashed seven-dimensional Sasaki-Einstein manifolds. Such reductions are of interest, for example, in that they have $(2+1)$-dimensional holographic duals, and the fermionic content and their interactions with charged scalars are an important aspect of their applications. We derive the lower-dimensional equations of motion for the fermions and exhibit their couplings to the various bosonic modes present in the truncations under consideration, which most notably include charged scalar and form fields. We demonstrate that our results are consistent with the expected supersymmetric structure of the lower dimensional theory, and apply them to a specific example which is relevant to the study of $(2+1)$-dimensional holographic superconductors.

hep-th↗