Publications from previous years
Publications 2018

Berends–Giele currents in Bern–CarrascoJohansson gauge for F^3 and F^4deformed Yang–Mills amplitudes
Authors: Lucia M. Garozzo, Leonel Queimada, Oliver Schlotterer
Preprint number: UUITP40/18
We construct new representations of treelevel amplitudes in Ddimensional gauge theories with deformations via highermassdimension operators \alpha' F^3 and \alpha'^2 F^4. Based on Berends—Giele recursions, the tensor structure of these amplitudes up to the order of \alpha’^2 is compactly organized via offshell currents. On the one hand, we present manifestly cyclic representations, where the complexity of the currents is systematically reduced. On the other hand, the duality between color and kinematics due to Bern, Carrasco and Johansson is manifested by means of nonlinear gauge transformations of the currents. We exploit the resulting notion of BernCarrascoJohansson gauge to provide explicit and manifestly local doublecopy representations for gravitational amplitudes involving \alpha' R^2 and \alpha'^2 R^3 operators.

The quantum swampland
Authors: Ulf H. Danielsson
Preprint number: UUITP39/18
In this paper we propose a quantum version of the swampland conjecture. We argue that quantum instabilities of de Sitter space discovered using field theoretical methods, are directly related to the difficulties in finding stringy de Sitter vacua.

(1,0) gauge theories on the sixsphere
Authors: Usman Naseer
Preprint number: UUITP38/18
We construct gauge theories with a vectormultiplet and hypermultiplets of (1,0) supersymmetry on the sixsphere. The gauge coupling on the sphere depends on the polar angle. This has a natural explanation in terms of the tensor branch of (1,0) theories on the sixsphere. For the vectormultiplet we give an offshell formulation for all supersymmetries. For hypermultiplets we give an offshell formulation for one supersymmetry. We show that the path integral for the vector multiplet localizes to solutions of the HermitianYangMills equation, which is a generalization of the (anti)self duality condition to higher dimensions. For the hypermultiplet, the path integral localizes to configurations where the field strengths of two complex scalars are related by an almost complex structure.

3d Mirror Symmetry from Sduality
Authors: Fabrizio Nieri, Yiwen Pan, Maxim Zabzine
Preprint number: UUITP37/18
We consider type IIB SL(2,Z) symmetry to relate the partition functions of different 5d supersymmetric Abelian linear quiver YangMills theories in the Ωbackground and squashed S5 background. By Higgsing Sdual theories, we extract new and old 3d mirror pairs. Generically, the Higgsing procedure yields 3d defects on intersecting spaces, and we derive new hyperbolic integral identities expressing the equivalence of the squashed S3 partition functions with additional degrees of freedom on the S1 intersection.

Formulae for Line Bundle Cohomology on CalabiYau Threefolds
Authors: Andrei Constantin and Andre Lukas
Preprint number: UUITP36/18
Abstract: We present closed form expressions for the ranks of all cohomology groups of holomorphic line bundles on several CalabiYau threefolds realised as complete intersections in products of projective spaces. The formulae have been obtained by systematising and extrapolating concrete calculations and they have been checked computationally. Although the intermediate calculations often involve laborious computations of ranks of Leray maps in the Koszul spectral sequence, the final results for cohomology follow a simple pattern. The space of line bundles can be divided into several different regions, and in each such region the ranks of all cohomology groups can be expressed as polynomials in the line bundle integers of degree at most three. The number of regions increases and case distinctions become more complicated for manifolds with a larger Picard number. We also find explicit cohomology formulae for several nonsimply connected CalabiYau threefolds realised as quotients by freely acting discrete symmetries. More cases may be systematically handled by machine learning algorithms.

Analytic Bootstrap for Boundary CFT
Authors: Agnese Bissi, Tobias Hansen, Alexander Söderberg
Preprint number: UUITP35/18
Abstract: We propose a method to analytically solve the bootstrap equation for two point functions in boundary CFT. We consider the analytic structure of the correlator in Lorentzian signature and in particular the discontinuity of bulk and boundary conformal blocks to extract CFT data. As an application, the correlator ⟨ϕϕ⟩ in ϕ^4 theory at the WilsonFisher fixed point is computed to order ϵ^2 in the ϵ expansion.

All fiveloop planar fourpoint functions of halfBPS operators in N=4 SYM
Authors : Dmitry Chicherin, Alessandro Georgoudis, Vasco Goncalves and Raul Pereira
Preprint number: UUITP34/18
We obtain all planar fourpoint correlators of halfBPS operators in N=4 SYM up to five loops. The ansatz for the integrand is fixed partially by imposing lightcone OPE relations between different correlators. We then fix the integrated correlators by comparing their asymptotic expansions with simple data obtained from integrability. We extract OPE coefficients and find a prediction for the triple wrapping correction of the hexagon form factors, which contributes already at the fiveloop order.

Bootstrapping the S5 partition function
Authors: Fabrizio Nieri, Yiwen Pan, Maxim Zabzine
Preprint number: UUITP33/18
Abstract: We consider U(N) SQCD on S5 and propose a Higgs branchlike expression for its partition function. We support the result by arguing that the knowledge of certain BPS codimension 2 and 4 defects arising from Higgsing is enough to reconstruct the bulk partition function, and that the defect partition functions satisfy a set of nonperturbative SchwingerDyson equations. We show that the result is consistent with, and naturally come from, the BPS/CFT perspective. In this language, the defect partition functions are identified with free boson correlators of the qVirasoro modular triple, and the constraint equations with Ward identities satisfied by the corresponding DotsenkoFateev qconformal blocks, providing a natural basis to expand the S5 partition function.

Surface defects in the D4D8 brane system
Authors: Giuseppe Dibitetto and Nicolò Petri
Preprint number: UUITP32/18
Abstract: A new class of exact supersymmetric solutions is derived within minimal d = 6 F(4) gauged supergravity. These flows are all characterized by a nontrivial radial profile for the 2form gauge potential included into the supergravity multiplet. In particular three solutions within this class are featured by an AdS3 foliation of the 6d background and by an AdS6 asymptotic geometry. Secondly, considering the simplest example of these, we give its massive IIA uplift describing a warped solution of the type AdS3 × S2 × S3 fibered over two intervals I _r × I_ξ . We interpret this background as the nearhorizon of a D4D8 system on which a bound state D2NS5D6 ends producing a surface defect. Finally we discuss its holographic dual interpretation in terms of a N = (0, 4) SCFT2 defect theory within the N = 2 SCFT5 dual to the AdS6 × S4 massive IIA warped vacuum.

On the atheorem in the Conformal Window
Authors: Vladimir Prochazka, Roman Zwicky
Preprint number: UUITP30/18
Abstract:
We show that for four dimensional gauge theories in the conformal window, the Euler anomaly, known as the $a$function, can be computed from a $2$point function of the trace of the energy momentum tensor making them more amenable to lattice simulations. Concretely, we derive an expression for the $a$function as an integral over the renormalisation scale of quantities related to $2$ and $3$point functions of the trace of the energy momentum tensor.The crucial ingredients are that the square of the field strength tensor is an exactly marginal operator at the Gaussian fixed point and that the relevant $3$point correlation function is finite when resummed to all orders. This allows us to define a scheme for which the $3$point contribution vanishes, thereby explicitly establishing the strong version of the $a$theorem for this class of theories.

AdS3 solutions with exceptional supersymmetry
Authors: Giuseppe Dibitetto, Gabriele Lo Monaco, Achilleas Passias, Nicolò Petri, Alessandro Tomasiello
Preprint number: UUITP29/18
Abstract: Among the possible superalgebras that contain the AdS3 isometries, two interesting possibilities are the exceptional F(4) and G(3). Their Rsymmetry is respectively SO(7) and G2, and the amount of supersymmetry N= 8 and N= 7. We find that there exist two (locally) unique solutions in type IIA supergravity that realize these superalgebras, and we provide their analytic expressions. In both cases, the internal space is obtained by a round sixsphere fibred over an interval, with an O8plane at one end. The Rsymmetry is the symmetry group of the sphere; in the G(3) case, it is broken to G2 by fluxes. We also find several numerical N= 1 solutions with G2 flavor symmetry, with various localized sources, including O2planes and O8planes.

Some remarks on (super)conformal KillingYano tensors
Authors: P.S. Howe, and U. Lindström
Preprint number: UUITP31/18
A KillingYano tensor is an antisymmetric tensor obeying a firstorder differential constraint similar to that obeyed by a Killing vector. In this article we consider generalisations of such objects, focusing on the conformal case. These generalised conformal KillingYano tensors are of mixed symmetry type and obey the constraint that the largest irreducible representation of o(n) contained in the tensor constructed from the firstderivative applied to such an object should vanish. Such tensors appear naturally in the context of spinning particles having N0 = 1 worldline supersymmetry and in the related problem of higher symmetries of Dirac operators. Generalisations corresponding to extended worldline supersymmetries and to spacetime super symmetry are discussed.

Holographic duals of fivedimensional SCFTs on a Riemann surface
Authors: Ibrahima Bah, Achilleas Passias and Peter Weck
Preprint number: UUITP28/18
We study the twisted compactifications of fivedimensional Seiberg SCFTs, with SU_M(2) x E_{N_f+1} flavor symmetry, on a generic Riemann surface that preserves four supercharges. The fivedimensional SCFTs are obtained from the decoupling limit of N D4branes probing a geometry of N_f<8 D8branes and an O8plane. In addition to the Rsymmetry, 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 fivedimensional SCFTs, the background flux for the SU_M(2) has a geometric origin, similar to the topological twist of the Rsymmetry. We argue that the resulting lowenergy threedimensional theories describe the dynamics on the worldvolume of the N D4branes wrapped on the Riemann surface in the O8/D8 background. The Riemann surface can be described as a curve in a CalabiYau threefold 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 worldvolume theories, thereby providing strong evidence that the threedimensional SCFTs exist in the lowenergy limit of the compactification of the fivedimensional SCFTs. We compute observables such as the free energy and the scaling dimensions of operators dual to D2brane probes; these have nontrivial dependence on the twist parameter for the U(1) in SU_M(2). The free energy exhibits the N^{5/2} scaling that is emblematic of fivedimensional SCFTs.

Emergent de Sitter cosmology from decaying AdS
Authors: Souvik Banerjee, Ulf Danielsson, Giuseppe Dibitetto, Suvendu Giri and Marjorie Schillo
Preprint number: UUITP27/18
Recent developments in string compactifications demonstrate obstructions to the simplest constructions of low energy cosmologies with positive vacuum energy. The existence of obstacles to creating scaleseparated de Sitter solutions indicates a UV/IR puzzle for embedding cosmological vacua in a unitary theory of quantum gravity. Motivated by this puzzle, we propose an embedding of positive energy FriedmannLemaîtreRobertsonWalker cosmology within string theory. Our proposal involves confining 4D gravity on a brane which mediates the decay from a nonsupersymmetric false AdS5 vacuum to a true vacuum. In this way, it is natural for a 4D observer to experience an effective positive cosmological constant coupled to matter and radiation, avoiding the need for scale separation or a fundamental de Sitter vacuum.

AdS2 x S7 solutions from D0  F1  D8 intersections
Authors: Giuseppe Dibitetto and Achilleas Passias
Preprint number: UUITP26/18We study an exhaustive analytic class of massive type IIA backgrounds preserving sixteen real supercharges and enjoying SL(2, R) x SO(8) bosonic symmetry. The corresponding geometry is described by AdS2 × S7 warped over a line, which turns out to emerge from taking the nearhorizon limit of D0  F1  D8 intersections. By studying the singularity structure of these solutions we find the possible presence of localized O8/D8 sources, as well as of fundamental strings smeared over the S7 . Finally we discuss the relation between the aforementioned solutions and the known AdS7 x S2 class through double analytic continuation.

General Relativity from Scattering Amplitudes
Authors: N.E.J. BjerrumBohr, Poul H. Damgaard, Guido Festuccia, Ludovic Planté and Pierre Vanhove
Preprint number: UUITP25/18
We outline the program to apply modern quantum field theory methods to calculate observables in classical general relativity through a truncation to classical terms of the multigraviton twobody onshell scattering amplitudes between massive fields. Since only longdistance interactions corresponding to nonanalytic pieces need to be included, unitarity cuts provide substantial simplifications for both postNewtonian and postMinkowskian expansions. We illustrate this quantum field theoretic approach to classical general relativity by computing the interaction potentials to second order in the postNewtonian expansion, as well as the scattering functions for two massive objects to second order in the postMinkowskian expansion. We also derive an allorder exact result for gravitational lightbylight scattering.

Unraveling conformal gravity amplitudes
Authors: Henrik Johansson, Gustav Mogull, Fei Teng
Preprint number: UUITP24/18
Conformal supergravity amplitudes are obtained from the doublecopy construction using gaugetheory amplitudes, and compared to direct calculations starting from conformal supergravity Lagrangians. We consider several different theories: minimal N = 4 conformal supergravity, nonminimal N = 4 BerkovitsWitten conformal supergravity, massdeformed versions of these theories, as well as supersymmetry truncations thereof. Coupling the theories to a YangMills sector is also considered. For all cases we give the gravity Lagrangians that the double copy implicitly generates. The two main results are: we determine a Lagrangian for the nonminimal BerkovitsWitten theory, and we uncover the doublecopy prescription for the minimal N = 4 conformal supergravity.

CalabiYau Manifolds and SU (3) Structure
Authors: Magdalena Larfors, Andre Lukas, Fabian Ruehle
Preprint number: UUITP23/18
We show that nontrivial SU(3) structures can be constructed on large classes of CalabiYau threefolds. Specifically, we focus on CalabiYau threefolds constructed as complete intersections inproducts of projective spaces, although we expect similar methods to apply to other constructions and also to CalabiYau fourfolds. Among the wide range of possible SU(3) structures we find StromingerHull systems, suitable for heterotic or type II string compactifications, on all complete intersection CalabiYau manifolds. These SU(3) structures of StromingerHull type have a nonvanishing and nonclosed threeform flux which needs to be supported by source terms in the associated Bianchi identity. We discuss the possibility of finding such source terms and present first steps towards their explicit construction. Provided suitable sources exist, our methods lead to CalabiYau compactifications of string theory with a non Ricciflat, physical metric which can be written down explicitly and in analytic form 
On the universality of latetime correlators in semiclassical 2d CFTs
Authors: Souvik Banerjee, JanWillem Bryan, Gideon Vos
Preprint number: UUITP22/18
In the framework of AdS3/ CFT2 correspondence, we present a systematic analysis of the late time thermalization of a two dimensional CFT state created by insertion of small number of heavy operators on the vacuum. We show that at late Lorentzian time, the universal features of this thermalization are solely captured by the eigenvalues of the monodromy matrix corresponding to the solutions of the uniformization equation. We discuss two different ways to extract the monodromy eigenvalues while bypassing the need for finding explicitly the full monodromy matrix  first, using a monodromy preserving diffeomorphism and second using ChenSimons formulation of gravity in AdS3. Both of the methods yield the same precise relation between the eigenvalues and the final black hole temperature at late Lorentzian time.

The Analytic Bootstrap for Large N ChernSimons Vector Models
Authors: Ofer Aharony, Luis F. Alday, Agnese Bissi, Ran Yacoby
Preprint number: UUITP21/18
Threedimensional ChernSimons vector models display an approximate higher spin symmetry in the large N limit. Their singletrace operators consist of a tower of weakly broken currents, as well as a scalar σ of approximate twist 1 or 2. We study the consequences of crossing symmetry for the fourpoint correlator of σ in a 1/N expansion, using analytic bootstrap techniques. To order 1/N we show that crossing symmetry fixes the contribution from the tower of currents, providing an alternative derivation of wellknown results by Maldacena and Zhiboedov. When σ has twist 1 its OPE receives a contribution from the exchange of σ itself with an arbitrary coefficient, due to the existence of a marginal sextic coupling. We develop the machinery to determine the corrections to the OPE data of doubletrace operators due to this, and to similar exchanges. This in turns allows us to fix completely the correlator up to three known truncated solutions to crossing. We then proceed to study the problem to order 1/N^2. We find that crossing implies the appearance of oddtwist doubletrace operators, and calculate their OPE coefficients in a large spin expansion. Also, surprisingly, crossing at order 1/N^2, implies nontrivial O(1/N) anomalous dimensions for eventwist doubletrace operators, even though such contributions do not appear in the fourpoint function at order 1/N (in the case where there is no scalar exchange). We argue that this phenomenon arises due to operator mixing. Finally, we analyse the bosonic vector model with a sextic coupling without gauge interactions, and determine the order 1/N^2 corrections to the dimensions of twist2 doubletrace operators.

Complete integrationbyparts reductions of the nonplanar hexagonbox via module intersections
Authors: Janko Böhm, Alessandro Georgoudis, Kasper J. Larsen, Hans Schönemann, Yang Zhang
Preprint number: UUITP16/18
We present the powerful moduleintersection integrationbyparts (IBP) method,
for multiloop Feynman integral reduction. With modern computational algebraic geome
try techniques, this new method manages to trim traditional IBP systems dramatically to
much simpler integralrelation systems on unitarity cuts. We demonstrate the power of this
method by the complete analytic reduction of twoloop fivepoint nonplanar hexagonbox integrals, with degreefour numerators, to the 73 master integrals. 
A massive class of N = 2 AdS(4) IIA solutions
Authors: Achilleas Passias, Daniel Prins, Alessandro Tomasiello
Preprint number: UUITP20/18
We initiate a classification of N=2 supersymmetric AdS(4) solutions of (massive) type IIA supergravity. The internal space is locally equipped with either an SU(2) or an identity structure. We focus on the SU(2) structure and determine the conditions it satisfies, dictated by supersymmetry. Imposing as an ansatz that the internal space is complex, we reduce the problem of finding solutions to a Riccati ODE, which we solve analytically. We obtain in this fashion a large number of new families of solutions, both regular as well as with localized O8planes and conical CalabiYau singularities. We also recover many solutions already discussed in the literature.

AdS Weight Shifting Operators
Authors: Miguel S. Costa and Tobias Hansen
Preprint number: UUITP19/18
We construct a new class of differential operators that naturally act on AdS harmonic functions. These are weight shifting operators that change the spin and dimension of AdS representations. Together with CFT weight shifting operators, the new operators obey crossing equations that relate distinct representations of the conformal group. We apply our findings to the computation of Witten diagrams, focusing on the particular case of cubic interactions and on massive, symmetric and traceless fields. In particular we show that tree level 4point Witten diagrams with arbitrary spins, both in the external fields and in the exchanged field, can be reduced to the action of weight shifting operators on similar 4point Witten diagrams where all fields are scalars. We also show how to obtain the conformal partial wave expansion of these diagrams using the new set of operators. In the case of 1loop diagrams with cubic couplings we show how to reduce them to similar 1loop diagrams with scalar fields except for a single external spinning field (which must be a scalar in the case of a twopoint diagram). As a bonus, we provide new CFT and AdS weight shifting operators for mixedsymmetry tensors.

Perturbing AdS(6) x S(4): linearised equations and spin2 spectrum
Authors: Achilleas Passias and Paul Richmond
Preprint number: UUITP18/18
We initiate the analysis of the KaluzaKlein mass spectrum of massive IIA supergravity on the warped AdS(6) x S(4) background, by deriving the linearised equations of motion of bosonic and fermionic fluctuations, and determining the mass spectrum of those of spin2. The spin2 modes are given in terms of hypergeometric functions and a careful analysis of their boundary conditions uncovers the existence of two branches of mass spectra, bounded from below. The modes that saturate the bounds belong to short multiplets which we identify in the representation theory of the f(4) symmetry superalgebra of the AdS(6) x S(4) solution.

Onepoint functions in βdeformed N = 4 SYM with defect
Author: Erik Widén
Preprint number: UUITP17/18
We generalize earlier results on onepoint functions in N = 4 SYM with a codimension one defect, dual to the D3D5brane setup in type IIB string theory on AdS5 × S5, to a similar setup in the βdeformed version of the theory. The treelevel vacuum expectation values of singletrace operators in the twoscalarsubsector are expressed as overlaps between a matrix product state (MPS) and Bethe states in the corresponding twisted spinchain picture. We comment on the properties of this MPS and present the simplest analytical overlaps and their behavior in a certain limit (of large k). Importantly, we note that the deformation alters earlier interpretations of the MPS as an integrable boundary state, seemingly obstructing simplifications of the overlaps analogous to the compact determinant formula found in the nondeformed theory. The results are supplemented with some supporting numerical results for operators of length eight with four excitations. 
Precision matching of circular Wilson loops and strings in AdS(5)xS(5)
Authors: Daniel MedinaRincon, Arkady A. Tseytlin and Konstantin Zarembo
Preprint number: UUITP15/18
Previous attempts to match the exact N=4 super YangMills expression for the expectation value of the 1/2BPS circular Wilson loop with the semiclassical AdS(5)xS(5) string theory prediction were not successful at the first subleading order. There was a missing prefactor lambda^(3/4) which could be attributed to the unknown normalization of the string path integral measure. Here we resolve this problem by computing, following arXiv:1712.07730, the ratio of the string partition functions corresponding to the circular Wilson loop and the special 1/4supersymmetric latitude Wilson loop. The fact that the latter has a trivial expectation value in the gauge theory allows us to relate the prefactor to the contribution of the three zero modes of the ``transverse" fluctuation operator in the 5sphere directions.

Morita equivalence and the generalized Kähler potential
Authors: Francis Bischoff, Marco Gualtieri and Maxim Zabzine
Preprint number: UUITP14/18
Abstract: We solve the problem of determining the fundamental degrees of freedom underlying a generalized K\"ahler structure of symplectic type. For a usual K\"ahler structure, it is wellknown that the geometry is determined by a complex structure, a K\"ahler class, and the choice of a positive (1,1)form in this class, which depends locally on only a single realvalued function: the K\"ahler potential. Such a description for generalized K\"ahler geometry has been sought since it was discovered in 1984. We show that a generalized K\"ahler structure of symplectic type is determined by a pair of holomorphic Poisson manifolds, a holomorphic symplectic Morita equivalence between them, and the choice of a positive Lagrangian brane bisection, which depends locally on only a single realvalued function, which we call the generalized K\"ahler potential. Our solution draws upon, and specializes to, the many results in the physics literature which solve the problem under the assumption (which we do not make) that the Poisson structures involved have constant rank. To solve the problem we make use of, and generalize, two main tools: the first is the notion of symplectic Morita equivalence, developed by Weinstein and Xu to study Poisson manifolds; the second is Donaldson's interpretation of a K\"ahler metric as a real Lagrangian submanifold in a deformation of the holomorphic cotangent bundle.

Ultraviolet Properties of N = 8 Supergravity at Five Loops
Authors: Zvi Bern, John Joseph Carrasco, WeiMing Chen, Alex Edison,
Henrik Johansson, Julio ParraMartinez, Radu Roiban and Mao ZengPreprint number: UUITP13/18
Abstract: We use the recently developed generalized doublecopy construction to obtain an improved representation of the fiveloop fourpoint integrand of N=8 supergravity whose leading ultraviolet behavior we analyze using state of the art loopintegral expansion and reduction methods. We find that the fiveloop critical dimension where ultraviolet divergences first occur is D_c=24/5, corresponding to a D^8 R^4 counterterm. This ultraviolet behavior stands in contrast to the cases of fourdimensional N=4 supergravity at three loops and N=5 supergravity at four loops whose improved ultraviolet behavior demonstrates enhanced cancellations beyond implications from standardsymmetry considerations. We express this D_c=24/5 divergence in terms of two relatively simple positivedefinite integrals reminiscent of vacuum integrals, excluding any additional ultraviolet cancellations at this looporder. We note nontrivial relations between the integrals describing this leading ultraviolet behavior and integrals describing lowerloop behavior. This observation suggests not only a path towards greatly simplifying future calculations at higher loops, but may even allow us to directly investigate ultraviolet behavior in terms of simplified integrals, avoiding the construction of complete integrands.

The nonAbelian tensor multiplet
Authors: Andreas Gustavsson
Preprint number: UUITP12/18
Abstract: We assume the existence of a background vector field that enables us to make an ansatz for the superconformal transformations for the nonAbelian 6d (1,0) tensor multiplet. Closure of supersymmetry on generators of the conformal algebra, requires that the vector field is Abelian, has scaling dimension minus one and that the supersymmetry parameter as well as all the fields in the tensor multiplet have vanishing Lie derivatives along this vector field. We couple the tensor multiplet to a hypermultiplet and obtain superconformal transformations that we close offshell.

The Conformal Anomaly in bCFT from Momentum Space Perspective
Authors: Vladimir Prochazka
Preprint number: UUITP11/18
Abstract: We study the momentum space representation of energymomentum tensor twopoint functions on a space with a planar boundary in d=3. We show that nonconservation of momentum in the direction perpendicular to the boundary allows for new phenomena compared to the boundaryless case. Namely we demonstrate how local contact terms arise when the correlators are expanded in the regime where parallel momentum is small compared to the perpendicular one, which corresponds to the nearboundary limit. By exploring twoderivative counterterms involving components of Riemann tensor we identify a finite, schemeindependent part of the twopoint function. We then relate this component to the conformal anomaly $c_∂$ proportional to the boundary curvature R̂ . In the formalism of this paper $c_∂$ arises due to integrating out bulk modes coupled to the curved space, which generate local contributions the effective action at the boundary. To calculate the anomaly in specific (freefield) examples, we combine the method of images with Feynman diagrammatic techniques and propose a general methodology for perturbative computations of this type. The framework is tested by computing $c_∂$ on the explicit example of free scalar with mixed boundary conditions where we find agreement with the literature.

What if string theory has no de Sitter vacua?
Authors: Ulf H. Danielsson and Thomas Van Riet
Preprint number: UUITP10/18
Abstract: We present a brief overview of attempts to construct de Sitter vacua in string theory and explain how the results of this 20year endeavor could point to the fact that string theory harbors no de Sitter vacua at all. Making such a statement is often considered controversial and "bad news for string theory". We discuss how perhaps the opposite can be true.

The holographic interpretation of J\overline{T}deformed CFTs
Authors: Adam Bzowski and Monica Guica
Preprint number: UUITP09/18
Abstract: Recently, a nonlocal yet possibly UVcomplete quantum field theory has been constructed by deforming a twodimensional CFT by the composite operator J\overline{T}, where J is a chiral U(1) current and \overline{T} is a component of the stress tensor. Assuming the original CFT was a holographic CFT, we work out the holographic dual of its J\overline{T} deformation. We find that the dual spacetime is still AdS3, but with modified boundary conditions that mix the metric and the ChernSimons gauge field dual to the U(1) current. We show that the energy and thermodynamics of black holes obeying these modified boundary conditions precisely reproduce the previously derived field theory spectrum and thermodynamics, provided the contribution of the current takes a particular form we motivate. The associated asymptotic symmetry group consists of two copies of the Virasoro and one copy of the U(1) KacMoody algebra, just as before the deformation; the only effect of the latter is to modify the spacetime dependence of the rightmoving Virasoro generators, whose action becomes statedependent and effectively nonlocal.

Uses of Sigma Models
Author: Ulf Lindström
Preprint number: UUITP08/18
Abstract: This is a brief review of some of the uses of nonlinear sigma models. After a short general discussion touching on point particles, strings and condensed matter systems , focus is shifted to sigma models as probes of target space geometries. The relation of supersymmetric nonlinear sigma models to Kähler, hyperkähler, hyperkähler with torsion and generalised Kähler geometries is described.

Heterotic and bosonic string amplitudes via field theory
Authors: Thales Azevedo, Marco Chiodaroli, Henrik Johansson and Oliver Schlotterer
Preprint number: UUITP07/18
Previous work has shown that massless tree amplitudes of the type I and IIA/B superstrings can be dramatically simplified by expressing them as double copies between fieldtheory amplitudes and scalar disk/sphere integrals, the latter containing all the $\alpha'$corrections. In this work, we pinpoint similar doublecopy constructions for the heterotic and bosonic string theories using an $\alpha'$dependent field theory and the same disk/sphere integrals. Surprisingly, this field theory, built out of dimensionsix operators such as $(D_\mu F^{\mu \nu})^2$, has previously appeared in the doublecopy construction of conformal supergravity. We elaborate on the $\alpha' \rightarrow \infty$ limit in this picture and derive new amplitude relations for various gaugegravity theories from those of the heterotic string.

Infinitely Many M2instanton Corrections to Mtheory on G_2 manifolds
Authors: Andreas P. Braun, Michele Del Zotto, James Halverson, Magdalena Larfors, David R. Morrison and Sakura SchäferNameki
Preprint number: UUITP06/18
We consider the nonperturbative superpotential for a class of fourdimensional N = 1 vacua obtained from Mtheory on sevenmanifolds with holonomy $G_2$. The class of $G_2$holonomy manifolds we consider are socalled twisted connected sum (TCS) constructions, which have the topology of a K3fibration over $S^3$. We show that the nonperturbative superpotential of Mtheory on a class of TCS geometries receives infinitely many inequivalent M2instanton contributions from infinitely many threespheres, which we conjecture are supersymmetric (and thus associative) cycles. The rationale for our construction is provided by the duality chain of [1], which relates Mtheory on TCS $G_2$manifolds to $E_8 \times E_8$ heterotic backgrounds on the Schoen CalabiYau threefold, as well as to Ftheory on a K3fibered CalabiYau fourfold. The latter are known to have an infinite number of instanton corrections to the superpotential and it is these contributions that we trace through the duality chain back to the $G_2$compactification.

4D Gauge Theories with Conformal Matter
Authors: Fabio Apruzzi, Jonathan J. Heckman, David R. Morrison and Luigi Tizzano
Preprint number: UUITP05/18
One of the hallmarks of 6D superconformal field theories (SCFTs) is that on a partial tensor branch, all known theories resemble quiver gauge theories with links comprised of 6D conformal matter, a generalization of weakly coupled hypermultiplets. In this paper we construct 4D quiverlike gauge theories in which the links are obtained from compactifications of 6D conformal matter on Riemann surfaces with flavor symmetry fluxes. This includes generalizations of super QCD with exceptional gauge groups and quarks replaced by 4D conformal matter. Just as in super QCD, we find evidence for a conformal window as well as confining gauge group factors depending on the total amount of matter. We also present Ftheory realizations of these field theories via elliptically fibered CalabiYau fourfolds. Gauge groups (and flavor symmetries) come from 7branes wrapped on surfaces, conformal matter localizes at the intersection of pairs of 7branes, and Yukawas between 4D conformal matter localize at points coming from triple intersections of 7branes. Quantum corrections can also modify the classical moduli space of the Ftheory model, matching expectations from effective field theory.

Fiveloop massless propagator integrals
Authors: Alessandro Georgoudis, Vasco Goncalves, Erik Panzer and Raul Pereira
Preprint number: UUITP02/18
We develop a method to obtain εexpansions of massless twopoint
integrals in position space, based on the constraints implied by symmetries of
the asymptotic expansion of conformal fourpoint integrals. Together with
parametric integration, we are able to fix the expansions of 170 genuine
fiveloop master integrals. In particular, we computed the expansions of all
planar master integrals up to transcendental weight 9. 
Matter Field Kahler Metric in Heterotic String Theory from Localisation
Authors: Stefan Blesneag, Evgeny I. Buchbinder, Andrei Constantin, Andre Lukas, Eran Palti
Preprint Number: UUITP04/18
Abstract: We propose an analytic method to calculate the matter field Kähler metric in heterotic compactifications on smooth CalabiYau threefolds with Abelian internal gauge fields. The matter field Kähler metric determines the normalisations of the N = 1 chiral superfields, which enter the computation of the physical Yukawa couplings. We first derive the general formula for this Kähler metric by a dimensional reduction of the relevant supergravity theory and find that its Tmoduli dependence can be determined in general. It turns out that, due to large internal gauge flux, the remaining integrals localise around certain points on the compactification manifold and can, hence, be calculated approximately without precise knowledge of the Ricciflat CalabiYau metric. In a final step, we show how this local result can be expressed in terms of the global moduli of the CalabiYau manifold. The method is illustrated for the family of CalabiYau hypersurfaces embedded in P1 × P3 and we obtain an explicit result for the matter field Kähler metric in this case.

Permutation in the CHYFormulation
Authors: Rijun Huang, Fei Teng and Bo Feng
Preprint Number: UUITP03/18
Abstract: The CHYintegrand of biadjoint cubic scalar theory is a product of two PTfactors. This pair of PTfactors can be interpreted as defining a permutation. We introduced the cycle representation of permutation in this paper for the understanding of cubic scalar amplitude. We showed that, given a permutation related to the pair of PTfactors, the pole and vertex information of Feynman diagrams of corresponding CHYintegrand is completely characterized by the cycle representation of permutation. Inversely, we also showed that, given a set of Feynman diagrams, the cycle representation of corresponding PTfactor can be recursively constructed from three point ones. Based on these results, we have investigated the relations among different independent pairs of PTfactors in the context of cycle representation as well as the multiplication of crossratio factors.

Superconformal indices on $S^1\times (S^5/\mathbb{Z}_p)$
Authors: Andreas Gustavsson
Preprint number: UUITP01/18
We obtain generating functions associated to the abelian superconformal indices for 6d $(1,0)$ tensor and hypermultiplets on $S^1\times (S^5/\mathbb{Z}_p)$. We extract the superconformal indices and their high and low temperature behaviors. We consider round and generically squashed $S^5$ in turn. We show that the unsquashed limit of the superconformal indices is smooth. We examine Sduality in the large $p$ limit that acts by exchanging the Hopf circle with the temporal circle.