Mirror Symmetry We prove mirror symmetry for supersymmetric sigma models on Kahler manifolds in 1 + 1 dimensions. The proof involves establishing the equivalence of the gauged linear sigma model, embedded in a theory with an enlarged gauge symmetry, with a Landau-Ginzburg theory of Toda type. Standard R → 1/R duality and dynamical generation of superpotential by vortices are crucial in the derivation. This provides not only a proof of mirror symmetry in the case of (local and global) Calabi-Yau manifolds, but also for sigma models on manifolds with positive first Chern class, including deformations of the action by holomorphic isometries.

Linking Starobinsky-Type Inflation in no-Scale Supergravity to MSSM A novel realization of the Starobinsky inflationary model within a moderate extension of the Minimal Supersymmetric Standard Model (MSSM) is presented. The proposed superpotential is uniquely determined by applying a continuous R and a Z2 discrete symmetry, whereas the K¨ahler potential is associated with a no-scale-type SU(54, 1)/SU(54)×U(1)R × Z2 K¨ahler manifold. The inflaton is identified with a Higgs-like modulus whose the vacuum expectation value controls the gravitational strength. Thanks to a strong enough coupling (with a parameter cT involved) between the inflaton and the Ricci scalar curvature, inflation can be attained even for subplanckian values of the inflaton with cT ≥ 76 and the corresponding effective theory being valid up to the Planck scale. The inflationary observables turn out to be in agreement with the current data and the inflaton mass is predicted to be 3 · 1013 GeV. At the cost of a relatively small superpotential coupling constant, the model offers also a resolution of the µ problem of MSSM. Supplementing MSSM by three right-handed neutrinos we show that spontaneously arising couplings between the inflaton and the particle content of MSSM not only ensure a sufficiently low reheating temperature but also support a scenario of non-thermal leptogenesis consistently with the neutrino oscillation parameters for gravitino heavier than about 104 GeV.

Lectures on Mirror Symmetry and Topological String Theory These are notes of a series of lectures on mirror symmetry and topological string theory given at the Mathematical Sciences Center at Tsinghua University. The N = 2 superconformal algebra, its deformations and its chiral ring are reviewed. A topological field theory can be constructed whose observables are only the elements of the chiral ring. When coupled to gravity, this leads to topological string theory. The identification of the topological string A- and Bmodels by mirror symmetry leads to surprising connections in mathematics and provides tools for exact computations as well as new insights in physics. A recursive construction of the higher genus amplitudes of topological string theory expressed as polynomials is reviewed.

Unified Model of Chaotic Inflation and Dynamical Supersymmetry Breaking The large hierarchy between the Planck scale and the weak scale can be explained by the dynamical breaking of supersymmetry in strongly coupled gauge theories. Similarly, the hierarchy between the Planck scale and the energy scale of inflation may also originate from strong dynamics, which dynamically generate the inflaton potential. We present a model of the hidden sector which unifies these two ideas, i.e., in which the scales of inflation and supersymmetry breaking are provided by the dynamics of the same gauge group. The resultant inflation model is chaotic inflation with a fractional power-law potential in accord with the upper bound on the tensor-to-scalar ratio. The supersymmetry breaking scale can be much smaller than the inflation scale, so that the solution to the large hierarchy problem of the weak scale remains intact. As an intrinsic feature of our model, we find that the sgoldstino, which might disturb the inflationary dynamics, is automatically stabilized during inflation by dynamically generated corrections in the strongly coupled sector. This renders our model a field-theoretical realization of what is sometimes referred to as sgoldstino-less inflation.

Gauge supergravity in D = 2 + 2 We present an action for chiral N = (1, 0) supergravity in 2+2 dimensions. The fields of the theory are organized into an OSp(1|4) connection supermatrix, and are given by the usual vierbein Va, spin connection ωab, and Majorana gravitino ψ. In analogy with a construction used for D = 10 + 2 gauge supergravity, the action is given by R ST r(R2Γ), where R is the OSp(1|4) curvature supermatrix two-form, and Γ a constant supermatrix containing γ5. It is similar, but not identical to the MacDowell-Mansouri action for D = 2 + 2 supergravity. The constant supermatrix breaks OSp(1|4) gauge invariance to a subalgebra OSp(1|2) ⊕ Sp(2), including a Majorana-Weyl supercharge. Thus half of the OSp(1|4) gauge supersymmetry survives. The gauge fields are the selfdual part of ωab and the Weyl projection of ψ for OSp(1|2), and the antiselfdual part of ωab for Sp(2). Supersymmetry transformations, being part of a gauge superalgebra, close off-shell. The selfduality condition on the spin connection can be consistently imposed, and the resulting “projected” action is OSp(1|2) gauge invariant.

Are all supergravity theories Yang-Mills squared? Using simple symmetry arguments we classify the ungauged D = 4, N = 2 supergravity theories, coupled to both vector and hyper multiplets through homogeneous scalar manifolds, that can be built as the product of N = 2 and N = 0 matter-coupled Yang-Mills gauge theories. This includes all such supergravities with two isolated exceptions: pure supergravity and the T3 model.

The kinematical Setup of Quantum Geometry In this article we present a brief introduction to the kinematical setup that underlies the quantization used in loop quantum gravity. This review has been published as a chapter in the monograph "Loop Quantum Gravity: The First 30 Years", edited by Abhay Ashtekar and Jorge Pullin, that was recently published in the series "100 Years of General Relativity" [1].

D-branes and Orientifolds in Calabi–Yau Compactifications We explore the dynamics of nonsupersymmetric D-brane configurations on Calabi-Yau orientifolds with fluxes. We show that supergravity D-terms capture supersymmetry breaking effects predicted by more abstract Π-stability considerations. We also investigate the vacuum structure of such configurations in the presence of fluxes. Based on the shape of the potential, we argue that metastable nonsupersymmetric vacua can be in principle obtained by tuning the values of fluxes. We also develop computational tools for the tree-level superpotential of B-branes in CalabiYau orientifolds. Our method is based on a systematic implementation of the orientifold projection in the geometric approach of Aspinwall and Katz. In the process we lay down some ground rules for orientifold projections in the derived category.

Does time-symmetry in quantum theory imply retrocausality? Although there are many counterintuitive ideas in quantum theory, the idea that influences can travel backwards in time (from the future to the past) is generally not one of them. However, recently some physicists have been looking into this idea, called "retrocausality," because it can potentially resolve some long-standing puzzles in quantum physics. In particular, if retrocausality is allowed, then the famous Bell tests can be interpreted as evidence for retrocausality and not for action-at-a-distance—a result that Einstein and others skeptical of that "spooky" property may have appreciated. n a new paper published in Proceedings of The Royal Society A, physicists Matthew S. Leifer at Chapman University and Matthew F. Pusey at the Perimeter Institute for Theoretical Physics have lent new theoretical support for the argument that, if certain reasonable-sounding assumptions are made, then quantum theory must be retrocausal. The appeal of retrocausality First, to clarify what retrocausality is and isn't: It does not mean that signals can be communicated from the future to the past—such signaling would be forbidden even in a retrocausal theory due to thermodynamic reasons. Instead, retrocausality means that, when an experimenter chooses the measurement setting with which to measure a particle, that decision can influence the properties of that particle (or another particle) in the past, even before the experimenter made their choice. In other words, a decision made in the present can influence something in the past. In the original Bell tests, physicists assumed that retrocausal influences could not happen. Consequently, in order to explain their observations that distant particles seem to immediately know what measurement is being made on the other, the only viable explanation was action-at-a-distance. That is, the particles are somehow influencing each other even when separated by large distances, in ways that cannot be explained by any known mechanism. But by allowing for the possibility that the measurement setting for one particle can retrocausally influence the behavior of the other particle, there is no need for action-at-a-distance—only retrocausal influence. Generalizing retrocausality: with or without a real quantum state One of the main proponents of retrocausality in quantum theory is Huw Price, a philosophy professor at the University of Cambridge. In 2012, Price laid out an argument suggesting that any quantum theory that assumes that 1) the quantum state is real, and 2) the quantum world is time-symmetric (that physical processes can run forwards and backwards while being described by the same physical laws) must allow for retrocausal influences. Understandably, however, the idea of retrocausality has not caught on with physicists in general. "There is a small group of physicists and philosophers that think this idea is worth pursuing, including Huw Price and Ken Wharton [a physics professor at San José State University]," Leifer told Phys.org. "There is not, to my knowledge, a generally agreed upon interpretation of quantum theory that recovers the whole theory and exploits this idea. It is more of an idea for an interpretation at the moment, so I think that other physicists are rightly skeptical, and the onus is on us to flesh out the idea." In the new study, Leifer and Pusey attempt to do this by generalizing Price's argument, which perhaps makes it more appealing in light of other recent research. They begin by removing Price's first assumption, so that the argument holds whether the quantum state is real or not—a matter that is still of some debate. A quantum state that is not real would describe physicists' knowledge of a quantum system rather than being a true physical property of the system. Although most research suggests that the quantum state is real, it is difficult to confirm one way or the other, and allowing for retrocausality may provide insight into this question. Allowing for this openness regarding the reality of the quantum state is one of the main motivations for investigating retrocausality in general, Leifer explained. "The reason I think that retrocausality is worth investigating is that we now have a slew of no-go results about realist interpretations of quantum theory, including Bell's theorem, Kochen-Specker, and recent proofs of the reality of the quantum state," he said. "These say that any interpretation that fits into the standard framework for realist interpretations must have features that I would regard as undesirable. Therefore, the only options seem to be to abandon realism or to break out of the standard realist framework. "Abandoning realism is quite popular, but I think that this robs science of much of its explanatory power and so it is better to find realist accounts where possible. The other option is to investigate more exotic realist possibilities, which include retrocausality, relationalism, and many-worlds. Aside from many-worlds, these have not been investigated much, so I think it is worth pursuing all of them in more detail. I am not personally committed to the retrocausal solution over and above the others, but it does seem possible to formulate it rigorously and investigate it, and I think that should be done for several of the more exotic possibilities." Can't have both time symmetry and no-retrocausality In their paper, Leifer and Pusey also reformulate the usual idea of time symmetry in physics, which is based on reversing a physical process by replacing t with –t in the equations of motion. The physicists develop a stronger concept of time symmetry here in which reversing a process is not only possible but that the probability of occurrence is the same whether the process is going forward or backward. The physicists' main result is that a quantum theory that assumes both this kind of time symmetry and that retrocausality is not allowed runs into a contradiction. They describe an experiment illustrating this contradiction, in which the time symmetry assumption requires that the forward and backward processes have the same probabilities, but the no-retrocausality assumption requires that they are different. So ultimately everything boils down to the choice of whether to keep time symmetry or no-retrocausality, as Leifer and Pusey's argument shows that you can't have both. Since time symmetry appears to be a fundamental physical symmetry, they argue that it makes more sense to allow for retrocausality. Doing so would eliminate the need for action-at-a-distance in Bell tests, and it would still be possible to explain why using retrocausality to send information is forbidden. "The case for embracing retrocausality seems stronger to me for the following reasons," Leifer said. "First, having retrocausality potentially allows us to resolve the issues raised by other no-go theorems, i.e., it enables us to have Bell correlations without action-at-a-distance. So, although we still have to explain why there is no signaling into the past, it seems that we can collapse several puzzles into just one. That would not be the case if we abandon time symmetry instead. "Second, we know that the existence of an arrow of time already has to be accounted for by thermodynamic arguments, i.e., it is a feature of the special boundary conditions of the universe and not itself a law of physics. Since the ability to send signals only into the future and not into the past is part of the definition of the arrow of time, it seems likely to me that the inability to signal into the past in a retrocausal universe could also come about from special boundary conditions, and does not need to be a law of physics. Time symmetry seems less likely to emerge in this way (in fact, we usually use thermodynamics to explain how the apparent time asymmetry that we observe in nature arises from time-symmetric laws, rather than the other way round)." As the physicists explain further, the whole idea of retrocausality is so difficult to accept because we don't ever see it anywhere else. The same is true of action-at-a-distance. But that doesn't mean that we can assume that no-retrocausality and no-action-at-a-distance are true of reality in general. In either case, physicists want to explain why one of these properties emerges only in certain situations that are far removed from our everyday observations. "One way of looking at all the no-go theorems is in terms of fine-tunings," Leifer explained. "You notice a property of the predictions of the theory and you assume that this property is also true of reality. Then you show that this is incompatible with reproducing the predictions of quantum theory and you have a no-go theorem. "For example, in Bell's Theorem, we notice that we cannot send superluminal signals so we assume there are no superluminal influences in reality, but this gets us into conflict with the experimentally observed predictions. Notice that it is not really superluminal influences per se that are the biggest problem. If we were able to send signals faster than light we would simply say, 'Oh well, Einstein was wrong. Relativity theory is just incorrect.' And then get on with doing physics. But that is not what happened: no signaling still holds on the level of what we observe, it is just that there is a tension between this and what must be going on in reality to reproduce what we observe. If there are superluminal influences, then why can't we observe them directly? This is the puzzle that cries out for explanation." Implications and questioning assumptions If retrocausality is a feature of the quantum world, then it would have vast implications for physicists' understanding of the foundations of quantum theory. Perhaps the biggest significance is the implication for the Bell tests, showing that distant particles really cannot influence each other, but rather—as Einstein and others believed—that quantum theory is incomplete. If the new results are true, then retrocausality may be one of the missing pieces that makes quantum theory complete. "I think that different interpretations [of quantum theory] have different implications for how we might go about generalizing standard quantum theory," Leifer said. "This might be needed to construct the correct theory of quantum gravity, or even to resolve some issues in high-energy physics given that the unification of the other three forces is still up in the air in the light of LHC results. So I think that future theories built on the ideas of existing interpretations are where we might see a difference, but admittedly we are quite far from figuring out how this might work at present. "Speculatively, if there is retrocausality in the universe, then it might be the case that there are certain eras, perhaps near the big bang, in which there is not a definite arrow of causality. You might imagine that a signature of such an era might show up in cosmological data, such as the cosmic microwave background. However, this is very speculative, and I have no idea what signatures we might expect yet." The physicists don't have any experiments lined up to test retrocausality—but as the idea is more an interpretation of observations rather than making new observations, what's needed most may not be a test but more theoretical support. "As far as direct experimental tests of retrocausality go, the status is not much different from other things in the foundations of quantum mechanics," Leifer said. "We never test one assumption in isolation, but always in conjunction with many others, and then we have to decide which one to reject on other grounds. For example, you might think that Bell experiments show that nature is nonlocal, but only if you have first decided to accept other assumptions, such as realism and no-retrocausality. So, you might say that Bell experiments already provide evidence for retrocausality if you are disinclined to reject realism or locality. Similarly, the kind of experiments we describe in our paper provide some evidence for retrocausality, but only if you refuse to reject the other assumptions. "In fact, the situation is really the same in all scientific experiments. There are a host of assumptions about the workings of the experimental apparatus that you have to accept in order to conclude that the experiment shows the effect you are looking for. It is just that, in the case of quantum foundations, the subject is very controversial, so we are more likely to question basic assumptions than we are in the case of, say, a medical drug trial. However, such assumptions are always there and it is always possible to question them."        

Flux Superpotential in Heterotic M–theory We derive the most general flux–induced superpotential for N = 1 M– theory compactifications on seven–dimensional manifolds with SU(3) structure. Imposing the appropriate boundary conditions, this result applies for heterotic M–theory. It is crucial for the latter to consider SU(3) and not G2 group structure on the seven–dimensional internal space. For a particular background that differs from CY (3) × S 1/Z2 only by warp factors, we investigate the flux–generated scalar potential as a function of the orbifold length. We find a positive cosmological constant minimum, however at an undesirably large value of this length. Hence the flux superpotential alone is not enough to stabilize the orbifold length at a de Sitter vacuum. But it does modify substantially the interplay between the previously studied non–perturbative effects, possibly reducing the significance of open membrane instantons while underlining the importance of gaugino condensation.

Five-brane Instantons vs Flux-induced Gauging of Isometries In five-dimensional heterotic M-theory there is necessarily nonzero background flux, which leads to gauging of an isometry of the universal hypermultiplet moduli space. This isometry, however, is poised to be broken by M5-brane instanton effects. We show that, similarly to string theory, the background flux allows only brane instantons that preserve the above isometry. The zeromode counting for the M5 instantons is related to the number of solutions of the Dirac equation on their worldvolume. We investigate that equation in the presence of generic background flux and also, in a particular case, with nonzero worldvolume flux.

Metastable SUSY Breaking and Supergravity at Finite Temperature We study how coupling to supergravity affects the phase structure of a system exhibiting dynamical supersymmetry breaking in a metastable vacuum. More precisely, we consider the Seiberg dual of SQCD coupled to supergravity at finite temperature. We show that the gravitational interactions decrease the critical temperature for the second order phase transition in the quark direction, that is also present in the global case. Furthermore, we find that, due to supergravity, a new second order phase transition occurs in the meson direction, whenever there is a nonvanishing constant term in the superpotential. Notably, this phase transition is a necessary condition for the fields to roll, as the system cools down, towards the metastable susy breaking vacuum, because of the supergravity-induced shift of the metastable minimum away from zero meson vevs. Finally, we comment on the phase structure of the KKLT model with uplifting sector given by the Seiberg dual of SQCD.

De Sitter Space in Gauge/Gravity Duality We investigate gauge/gravity duality for gauge theories in de Sitter space. More precisely, we study a five-dimensional consistent truncation of type IIB supergravity, which encompasses a wide variety of gravity duals of strongly coupled gauge theories, including the Maldacena-Nunez solution and its walking deformations. We find several solutions of the 5d theory with dS4 spacetime and nontrivial profiles for (some of) the scalars along the fifth (radial) direction. In the process, we prove that one of the equations of motion becomes dependent on the others, for nontrivial warp factor. This dependence reduces the number of field equations and, thus, turns out to be crucial for the existence of solutions with (A)dS4 spacetime. Finally, we comment on the implications of our dS4 solutions for building gravity duals of Glueball Inflation.

Higgsing and Seiberg-duality cascades from type IIB string theory We construct explicitly new solutions of type IIB supergravity with brane sources, the duals of which are N = 1 supersymmetric field theories exhibiting two very interesting phenomena. The far UV dynamics is controlled by a cascade of Seiberg dualities analogous to the Klebanov-Strassler backgrounds. At intermediate scales a cascade of Higgsing appears, in the sense that the gauge group undergoes a sequence of spontaneous symmetry breaking steps which reduces its rank. Deep in the IR, the theory confines, and the gravity background has a non-singular end of space. We explain in detail how to generate such solutions, discuss some of the Physics associated with them and briefly comment on the possible applications.

Glueball Inflation and Gauge/Gravity Duality We summarize our work on building glueball inflation models with the methods of the gauge/gravity duality. We review the relevant five-dimensional consistent truncation of type IIB supergravity. We consider solutions of this effective theory, whose metric has the form of a dS4 foliation over a radial direction. By turning on small (in an appropriate sense) time-dependent deformations around these solutions, one can build models of glueball inflation. We discuss a particular deformed solution, describing an ultra-slow roll inflationary regime.

Quantum Curves and Conformal Field Theory To a given algebraic curve we assign an infinite family of quantum curves (Schrödinger equations), which are in one-to-one correspondence with, and have the structure of, Virasoro singular vectors. For a spectral curve of a matrix model we build such quantum curves out of an appropriate representation of the Virasoro algebra, encoded in the structure of the α/β-deformed matrix integral and its loop equation. We generalize this construction to a large class of algebraic curves by means of a refined topological recursion. We also specialize this construction to various specific matrix models with polynomial and logarithmic potentials, and among other results, show that various ingredients familiar in the study of conformal field theory (Ward identities, correlation functions and a representation of Virasoro operators acting thereon, BPZ equations) arise upon specialization of our formalism to the multi-Penner matrix model.

Supersymmetric Gauge Theories and the AdS/CFT Correspondence In these lecture notes we first assemble the basic ingredients of supersymmetric gauge theories (particularly N=4 super-Yang-Mills theory), supergravity, and superstring theory. Brane solutions are surveyed. The geometry and symmetries of anti-de Sitter space are discussed. The AdS/CFT correspondence of Maldacena and its application to correlation functions in the the conformal phase of N=4 SYM are explained in considerable detail. A pedagogical treatment of holographic RG flows is given including a review of the conformal anomaly in four-dimensional quantum field theory and its calculation from five-dimensional gravity. Problem sets and exercises await the reader.

Statistical Inference and String Theory In this note we expose some surprising connections between string theory and statistical inference. We consider a large collective of agents sweeping out a family of nearby statistical models for an M-dimensional manifold of statistical fitting parameters. When the agents making nearby inferences align along a d-dimensional grid, we find that the pooled probability that the collective reaches a correct inference is the partition function of a non-linear sigma model in d dimensions. Stability under perturbations to the original inference scheme requires the agents of the collective to distribute along two dimensions. Conformal invariance of the sigma model corresponds to the condition of a stable inference scheme, directly leading to the Einstein field equations for classical gravity. By summing over all possible arrangements of the agents in the collective, we reach a string theory. We also use this perspective to quantify how much an observer can hope to learn about the internal geometry of a superstring compactification. Finally, we present some brief speculative remarks on applications to the AdS/CFT correspondence and Lorentzian signature spacetimes.

Strings 2017 Conference: Lectures and Videos  

Luis Fernando Alday	The Analytic Conformal Bootstrap	PDF	VIDEO
John Joseph Carrasco	Recent progress from amplitudes		VIDEO
Aristomenis Donos	Incoherent Transport and Black Holes	PDF	VIDEO
Thomas Dumitrescu	General Aspects of Renormalization Group Flows in Diverse Dimensions	PDF	VIDEO
Seok Kim	Advances in 5d/6d QFTs	PDF	VIDEO
Douglas Stanford	What’s up with the SYK model?	PDF	VIDEO
Pedro Vieira	Divide and Conquer. An Integrability Status Report		VIDEO
Special AdS/CFT Session
David Gross
Christopher Herzog	Applied AdS/CFT
Igor Klebanov
Juan Maldacena
Hirosi Ooguri	AdS/CFT in your everyday life
Edward Witten
Regular Talks
Nima Arkani-Hamed	Amplitudes and Correlators as Canonical Forms;  Worldsheets as Positive Geometries	PDF	VIDEO
Adam Brown	Complexity and Geometry		VIDEO
Simon Caron-Huot	Bulk Causality from the Conformal Bootstrap	PDF	VIDEO
Miranda Cheng	Progress on Moonshine	PDF	VIDEO
Sergei Dubovsky	QCD Strings and Jackiw-Teitelboim Gravity		VIDEO
Netta Engelhardt	The Apparent Horizon in AdS/CFT: Coarse Graining Entanglement
Valentina Forini	Green-Schwarz Superstring on a Lattice		VIDEO
Inaki Garcia-Etxebarria	New N=4 Theories in Four Dimensions	PDF	VIDEO
Yvonne Geyer	Ambitwistor Strings beyond Tree-level	PDF	VIDEO
Sergei Gukov	Disk Amplitudes and the Magnificent Three	PDF
Daniel Jafferis	Bulk Reconstruction and the Hartle-Hawking Wavefunction	PDF	VIDEO
Jared Kaplan	AdS_3/CFT_2 and the Information Paradox	PDF	VIDEO
David Kutasov	A Solvable Irrelevant Deformation of AdS_3/CFT_2	PDF
Karl Landsteiner	Anomalous Transport from Anti de-Sitter Space to Weyl Semimetals	PDF	VIDEO
Hong Liu	Emergent Entropy		VIDEO
R. Loganayagam	Out of Equilibrium, Out of Time Order	PDF	VIDEO
Juan Maldacena	Diving into Traversable Wormholes	PDF	VIDEO
Shiraz Minwalla	Flows, Fixed Points and Duality in Matter Chern Simons Theories	PDF	VIDEO
Robert Myers	Holographic Complexity	PDF	VIDEO
Joao Penedones	S-matrix Bootstrap Revisited		VIDEO
Suvrat Raju	Breakdown of String Perturbation Theory and Implications for Locality in Gravity		VIDEO
Leonardo Rastelli	How to Succeed at Holographic Correlators without Really Trying	PDF	VIDEO
Sakura Schafer-Nameki	F-theory and AdS_3/CFT_2	PDF	VIDEO
Nathan Seiberg	New Phases of QCD3 and QCD4	PDF	VIDEO
Ashoke Sen	Soft Graviton Theorem in Generic Quantum Theory of Gravity	PDF
Stephen Shenker	Black Holes and Random Matrices	PDF	VIDEO
Dam Thanh Son	Fractional Quantum Hall Effect and Duality	PDF	VIDEO
Andrew Strominger	Infrared Divergences in QED and Quantum Gravity		VIDEO
Yuji Tachikawa	Time-reversal Anomalies of 2+1d Topological Phases	PDF	VIDEO
Tadashi Takayanagi	AdS from Optimization of Path-Integrals in CFTs	PDF	VIDEO
Christoph Uhlemann	Holographic Duals for 5d SCFTs	PDF
Nicholas Warner	Microstate Geometries Deep Inside the Black-Hole Regime	PDF
Xi Yin	Genus Two Modular Bootstrap	PDF	VIDEO
Alexander Zhiboedov	Universal Correction to the Veneziano Amplitude	PDF	VIDEO
Gender and Diversity Issues
Marika Taylor	Gender and Diversity Issues		VIDEO

Bosonic D=11 Supergravity from a Generalized Chern-Simons Action It is shown that the action of the bosonic sector of D = 11 supergravity may be obtained by means of a suitable scaling of the originally dimensionless fields of a generalized Chern-Simons action. This follows from the eleven-form CS-potential of the most general linear combination of closed, gauge invariant twelve-forms involving the sp(32)-valued two-form curvatures supplemented by a three-form field. In this construction, the role of the skewsymmetric four-index auxiliary function needed for the first order formulation of D = 11 supergravity is played by the gauge field associated with the five Lorentz indices generator of the bosonic sp(32) subalgebra of osp(1|32).

Geometrodynamics: The Nonlinear Dynamics of Curved Spacetime We review discoveries in the nonlinear dynamics of curved spacetime, largely made possible by numerical solutions of Einstein’s equations. We discuss critical phenomena and self-similarity in gravitational collapse, the behavior of spacetime curvature near singularities, the instability of black strings in 5 spacetime dimensions, and the collision of four-dimensional black holes. We also discuss the prospects for further discoveries in geometrodynamics via observation of gravitational waves.

Supersymmetric Pati-Salam Models from Intersecting D6-branes: A Road to the Standard Model We provide a systematic construction of three-family N = 1 supersymmetric Pati-Salam models from Type IIA orientifolds on T6/(Z2×Z2) with intersecting D6-branes. All the gauge symmetry factors SU(4) C×SU(2) L×SU(2) R arise from the stacks of D6-branes with U(n) gauge symmetries, while the “hidden sector” is specified by USp(n) branes, parallel with the orientifold planes or their Z2 images. The Pati-Salam gauge symmetry can be broken down to the SU(3) C× SU(2) L×U(1) B − L×U(1) I3R via D6-brane splittings, and further down to the Standard Model via D- and F-flatness preserving Higgs mechanism from massless open string states in a N = 2 subsector. The models also possess at least two confining hidden gauge sectors, where gaugino condensation can in turn trigger supersymmetry breaking and (some) moduli stabilization. The systematic search yields 11 inequivalent models: 8 models with less than 9 Standard model Higgs doublet-pairs and 1 model with only 2 Standard Model Higgs doublet-pairs, 2 models possess at the string scale the gauge coupling unification of SU(2) L and SU(2) R, and all the models possess additional exotic matters. We also make preliminary comments on phenomenological implications of these models.

Quantum gravity in timeless configuration space On the path towards quantum gravity we find friction between temporal relations in quantum mechanics (QM) (where they are fixed and field-independent), and in general relativity (where they are field-dependent and dynamic). This paper aims to attenuate that friction, by encoding gravity in the timeless configuration space of spatial fields with dynamics given by a path integral. The framework demands that boundary conditions for this path integral be uniquely given, but unlike other approaches where they are prescribed — such as the no-boundary and the tunneling proposals — here I postulate basic principles to identify boundary conditions in a large class of theories. Uniqueness arises only if a reduced configuration space can be defined and if it has a profoundly asymmetric fundamental structure. These requirements place strong restrictions on the field and symmetry content of theories encompassed here; shape dynamics is one such theory. When these constraints are met, any emerging theory will have a Born rule given merely by a particular volume element built from the path integral in (reduced) configuration space. Also as in other boundary proposals, Time, including space-time, emerges as an effective concept; valid for certain curves in configuration space but not assumed from the start. When some such notion of time becomes available, conservation of (positive) probability currents ensues. I show that, in the appropriate limits, a Schroedinger equation dictates the evolution of weakly coupled source fields on a classical gravitational background. Due to the asymmetry of reduced configuration space, these probabilities and currents avoid a known difficulty of standard WKB approximations for Wheeler DeWitt in minisuperspace: the selection of a unique Hamilton-Jacobi solution to serve as background. I illustrate these constructions with a simple example of a full quantum gravitational theory (i.e. not in minisuperspace) for which the formalism is applicable, and give a formula for calculating gravitational semi-classical relative probabilities in it.

Suppressed SUSY for the SU(5) Grand Unified Supergravity Theory This paper starts with the most basic SU(5) Grand Unified Theory, coupled to Supergravity. Then it builds a new theory, incorporating the ideas of Suppressed SUSY. Suppressed SUSY is an alternative to the spontaneous breaking of SUSY. It does not need an invisible sector or explicit soft breaking of SUSY. It varies the content of the supermultiplets while keeping the restrictive nature of SUSY. For the simple model and sector constructed here, Suppressed SUSY has only three dimensionless parameters, plus the Planck mass. At tree level, this predicts a set of 8 different new masses, along with a cosmological constant that is naturally zero. The X and Y vector bosons get Planck scale masses 2√ 10g5MP. The five scalar multiplets that accompany the Higgs, and the Gravitino, all get colossally huge ‘SuperPlanck’ scale masses of order MSP ≈ 1017MP from a see-saw mechanism that arises from the theory. This new mass spectrum, the well-known SU(5) weak angle problem, and the cosmological constant value, should serve as guides for further modifications for the new Action.

Beyond the Cosmological Standard Model After a decade and a half of research motivated by the accelerating universe, theory and experiment have a reached a certain level of maturity. The development of theoretical models beyond Λ or smooth dark energy, often called modified gravity, has led to broader insights into a path forward, and a host of observational and experimental tests have been developed. In this review we present the current state of the field and describe a framework for anticipating developments in the next decade. We identify the guiding principles for rigorous and consistent modifications of the standard model, and discuss the prospects for empirical tests. We begin by reviewing recent attempts to consistently modify Einstein gravity in the infrared, focusing on the notion that additional degrees of freedom introduced by the modification must “screen” themselves from local tests of gravity. We categorize screening mechanisms into three broad classes: mechanisms which become active in regions of high Newtonian potential, those in which first derivatives of the field become important, and those for which second derivatives of the field are important. Examples of the first class, such as f(R) gravity, employ the familiar chameleon or symmetron mechanisms, whereas examples of the last class are galileon and massive gravity theories, employing the Vainshtein mechanism. In each case, we describe the theories as effective theories and discuss prospects for completion in a more fundamental theory. We describe experimental tests of each class of theories, summarizing laboratory and solar system tests and describing in some detail astrophysical and cosmological tests. Finally, we discuss prospects for future tests which will be sensitive to different signatures of new physics in the gravitational sector. The review is structured so that those parts that are more relevant to theorists vs. observers/experimentalists are clearly indicated, in the hope that this will serve as a useful reference for both audiences, as well as helping those interested in bridging the gap between them.

Computational complexity of the string-landscape/multiverse II – Cosmological considerations We propose a new approach for multiverse analysis based on computational complexity, which leads to a new family of “computational” measure factors. By defining a cosmology as a space-time containing a vacuum with specified properties (for example small cosmological constant) together with rules for how time evolution will produce the vacuum, we can associate global time in a multiverse with clock time on a supercomputer which simulates it. We argue for a principle of “limited computational complexity” governing early universe dynamics as simulated by this supercomputer, which translates to a global measure for regulating the infinities of eternal inflation. The rules for time evolution can be thought of as a search algorithm, whose details should be constrained by a stronger principle of “minimal computational complexity.” Unlike previously studied global measures, ours avoids standard equilibrium considerations and the well-known problems of Boltzmann Brains and the youngness paradox. We also give various definitions of the computational complexity of a cosmology, and argue that there are only a few natural complexity classes.

Taking up superspace—what would it take to be a realist about superspace? Supersymmetry is a crucial part of the string theoretic framework for a theory of quantum gravity. Supersymmetric theories (including those outside the context of string theory) present an interesting interpretative challenge. As a result of consistency conditions on the algebra of the supersymmetry (SUSY) generators, one is led to the idea that SUSY, although traditionally defined as a dynamical symmetry between bosons and fermions, could also be thought of as a spacetime symmetry in some extended spacetime, known as superspace. This paper focuses on what it would take to argue for an interpretation that favours the superspace formulation. I introduce a toy model of a supersymmetric field theory and argue for a special case of a more general thesis—that one needs some pre-existing philosophical commitment to favour one mathematical formulation over another. I then consider some extant positions from the literature on the philosophy of spacetime as candidates for such a position in the context of supersymmetric theories.

Liouville Action as Path-Integral Complexity: From Continuous Tensor Networks to AdS/CFT Abstract: We propose an optimization procedure for Euclidean path-integrals that evaluate CFT wave functionals in arbitrary dimensions. The optimization is performed by minimizing certain functional, which can be interpreted as a measure of computational complexity, with respect to background metrics for the path-integrals. In two dimensional CFTs, this functional is given by the Liouville action. We also formulate the optimization for higher dimensional CFTs and, in various examples, find that the optimized hyperbolic metrics coincide with the time slices of expected gravity duals. Moreover, if we optimize a reduced density matrix, the geometry becomes two copies of the entanglement wedge and reproduces the holographic entanglement entropy. Our approach resembles a continuous tensor network renormalization and provides a concrete realization of the proposed interpretation of AdS/CFT as tensor networks. The present paper is an extended version of our earlier report arXiv:1703.00456 and includes many new results such as evaluations of complexity functionals, energy stress tensor, higher dimensional extensions and time evolutions of thermofield double states.

D–Branes and T–Duality Recent developments in string theory have shown that p–brane solutions and duality symmetries play an important role in understanding the nonperturbative behaviour of the theory. An important example of a duality symmetry is the T–duality [1] which states that a string compactified on a torus with radius R is equivalent to a string compactified on a torus with radius α ′/R where α ′ is the inverse string tension. It turns out that the p–brane solutions whose charge are carried by a RR (Ramond/Ramond) gauge field of the type II supergravity theories have a natural place within open string theory as D–branes [2]. The relation is established via the requirement that the endpoints of the open string are constrained to live on the p+ 1–dimensional worldvolume of the Dirichlet p– brane. Such a (ten–dimensional) open string state is described by Dirichlet boundary conditions for the 9−p transverse directions and Neumann boundary conditions for the p + 1 worldvolume directions. Since under T–duality Dirichlet and Neumann boundary conditions are interchanged it follows that all Dirichlet p–branes (p = 0, · · · , 9) are T-dual versions of each other. A discussion of how this T–duality between D–branes arises in string theory can be found in the recent review article [3]. Since all D–branes are T–dual to each other it is natural to expect that this T–duality is also realized on the underlying p–brane solutions of the IIA/IIB supergravity theories. Furthermore, the T–duality should also be realized on the Dirichlet p–brane actions which act as source terms of the p–brane solutions. It is the purpose of this letter to give the details of this T–duality between Dirichlet p–brane solutions and their source terms and to point out a few subtleties that occur in establishing T–duality.

Timelike duality, M′-theory and an exotic form of the Englert solution Through timelike dualities, one can generate exotic versions of M-theory with different spacetime signatures. These are the M∗ -theory with signature (9, 2, −), the M′ -theory, with signature (6, 5, +) and the theories with reversed signatures (1, 10, −), (2, 9, +) and (5, 6, −). In (s, t, ±), s is the number of space directions, t the number of time directions, and ± refers to the sign of the kinetic term of the 3 form. The only irreducible pseudo-riemannian manifolds admitting absolute parallelism are, besides Lie groups, the seven-sphere S 7 ≡ SO(8)/SO(7) and its pseudo-riemannian version S 3,4 ≡ SO(4, 4)/SO(3, 4). [There is also the complexification SO(8, C)/SO(7, C), but it is of dimension too high for our considerations.] The seven-sphere S 7 ≡ S 7,0 has been found to play an important role in 11-dimensional supergravity, both through the Freund-Rubin solution and the Englert solution that uses its remarkable parallelizability to turn on non trivial internal fluxes. The spacetime manifold is in both cases AdS4 ×S 7 . We show that S 3,4 enjoys a similar role in M′ -theory and construct the exotic form AdS4 × S 3,4 of the Englert solution, with non zero internal fluxes turned on. There is no analogous solution in M∗ -theory.