Publikationer 2021

On the squashed sevensphere operator spectrum
Authors: S. Ekhammar, B. E. W. Nilsson
Preprint number: UUITP24/21
Abstract: We derive major parts of the eigenvalue spectrum of the operators on the squashed sevensphere that appear in the compactification of elevendimensional supergravity. These spectra determine the mass spectrum of the fields in AdS_{4} and are important for the corresponding N =1 supermultiplet structure. This work is a continuation of the work in [1] where the complete spectrum of irreducible isometry representations of the fields in AdS_{4} was derived for this compactification. Some comments are also made concerning the G_{2} holonomy and its implications on the structure of the operator equations on the squashed sevensphere.

Infrared Divergences and the Eikonal
Authors: Carlo Heissenberg
Preprint number: UUITP23/21
Abstract: The aim of this note is to explore the interplay between the eikonal resummation in impactparameter space and the exponentiation of infrared divergences in momentum space for gravity amplitudes describing collisions of massive objects. The eikonal governs the classical dynamics relevant to the twobody problem, and its infrared properties are directly linked to the zero frequency limit of the gravitational wave emission spectrum and to radiation reaction effects. Combining eikonal and infrared exponentiations it is possible to derive these properties at a given loop order starting from lowerloop data. This is illustrated explicitly in N = 8 supergravity and in general relativity by deriving the divergent part of the twoloop eikonal from treelevel and oneloop elastic amplitudes.

A higherdimensional view on quantum cosmology
Authors: U. H. Danielsson, D. Panizo, R. Tielemans, T. Van Riet
Preprint number: UUITP22/21
Abstract: We argue that the choice of boundary condition for the wavefunction in quantum cosmology depends on the UV completion of general relativity. We provide an explicit example using a braneworld scenario in which a de Sitter cosmology is induced on the surface of a CDL bubble in a 5dimensional AdS space. The corresponding boundary conditions are unambigously fixed by demanding consistency with the known physics of bubble nucleation and this selects the Vilenkin choice from a 4D viewpoint.

NexttoMHV YangMills kinematic algebra
Authors: Gang Chen, Henrik Johansson, Fei Teng and Tianheng Wang
Preprint number: UUITP21/21
Abstract: Kinematic numerators of YangMills scattering amplitudes possess a rich Lie algebraic structure that suggest the existence of a hidden infinitedimensional kinematic algebra. Explicitly realizing such a kinematic algebra is a longstanding open problem that only has had partial success for simple helicity sectors. In past work, we introduced a framework using tensor currents and fusion rules to generate BCJ numerators of a special subsector of NMHV amplitudes in YangMills theory. Here we enlarge the scope and explicitly realize a kinematic algebra for all NMHV amplitudes. Master numerators are obtained directly from the algebraic rules and through commutators and kinematic Jacobi identities other numerators can be generated. Inspecting the output of the algebra, we conjecture a closedform expression for the master BCJ numerator up to any multiplicity. We also introduce a new method, based on group algebra of the permutation group, to solve for the generalized gauge freedom of BCJ numerators. It uses the recently introduced binary BCJ relations to provide a complete set of NMHV kinematic numerators that consist of pure gauge.

New currents with KillingYano tensors
Authors: Ulf Lindström and Özgür Sarioglu
Preprint number: UUITP20/21
Abstract: New relations involving the Riemann, Ricci and Einstein tensors that have to hold for a given geometry to admit KillingYano tensors are described. These relations are then used to introduce novel conserved currents involving such KillingYano tensors. For a particular current based on the Einstein tensor, we discuss the issue of conserved charges and consider implications for the matter coupling to gravity. The condition on the background geometry to allow asymptotic conserved charges for a current introduced by Kastor and Traschen is found and a number of other new aspects of this current are commented on.

Bethe Algebra using Pure Spinors
Authors: Simon Ekhammar, Dmytro Volin
Preprint number: UUITP19/21
Abstract: We propose a gl(r)covariant parameterisation of Bethe algebra appearing in so(2r) integrable models, demonstrate its geometric origin from a fused flag, and use it to compute the spectrum of periodic rational spin chains, for various choices of the rank r and Drinfeld polynomials.

The Eikonal Approach to Gravitational Scattering and Radiation at O(G^3)
Authors: Paolo di Vecchia, Carlo Heissenberg, Rodolfo Russo, Gabriele Veneziano
Preprint number: UUITP18/21
Abstract: Using N=8 supergravity as a theoretical laboratory, we extract the 3PM gravitational eikonal for two colliding massive scalars from the classical limit of the corresponding elastic twoloop amplitude. We employ the eikonal phase to obtain the physical deflection angle and to show how its nonrelativistic (NR) and ultrarelativistic (UR) regimes are smoothly connected. Such a smooth interpolation rests on keeping contributions to the loop integrals originating from the full soft region, rather than restricting it to its potential subregion. This task is efficiently carried out by using the method of differential equations with complete nearstatic boundary conditions. In contrast to the potentialregion result, the physical deflection angle includes radiationreaction contributions that are essential for recovering the finite and universal UR limit implied by general analyticity and crossing arguments. We finally discuss the real emission of massless states, which accounts for the imaginary part of the 3PM eikonal and for the dissipation of energymomentum. Adopting a direct approach based on unitarity and on the classical limit of the inelastic treelevel amplitude, we are able to treat N=8 and General Relativity on the same footing, and to complete the conservative 3PM eikonal in Einstein's gravity by the addition of the radiationreaction contribution. We also show how this approach can be used to compute waveforms, as well as the differential and integrated spectra, for the different radiated massless fields.

Scattering Massive String Resonances through FieldTheory Methods
Authors: Max Guillen, Henrik Johansson, Renann Lipinski Jusinskas, Oliver Schlotterer
Preprint number: UUITP17/21
Abstract: We present a new method, exact in alpha', to explicitly compute string treelevel amplitudes involving one massive state and any number of massless ones. This construction relies on the socalled twisted heterotic string, which admits only gauge multiplets, a gravitational multiplet, and a single massive supermultiplet in its spectrum. In this simplified model, we determine the modulispace integrand of all amplitudes with one massive state using BerendsGiele currents of the gauge multiplet. These integrands are then straightforwardly mapped to gravitational amplitudes in the twisted heterotic string and to the corresponding massive amplitudes of the conventional typeI and typeII superstrings.

Monodromy Defects in Free Field Theories
Authors: Lorenzo Bianchi, Adam Chalabi, Vladimír Procházka, Brandon Robinson, and
Jacopo SistiPreprint number: UUITP 16/21
Abstract: We study codimension two monodromy defects in theories of conformally
coupled scalars and free Dirac fermions in arbitrary d dimensions. We characterise this
family of conformal defects by computing the onepoint functions of the stresstensor and
conserved current for Abelian flavour symmetries as well as twopoint functions of the
displacement operator. In the case of d = 4, the normalisation of these correlation functions
are related to defect Weyl anomaly coefficients, and thus provide crucial information about
the defect conformal field theory. We provide explicit checks on the values of the defect
central charges by calculating the universal part of the defect contribution to entanglement
entropy. Moreover, we leverage the nonsupersymmetric free field results to compute a
novel defect Weyl anomaly coefficient in a d = 4 theory of free N = 2 hypermultiplets.
In carefully studying the defect operator product expansion, we identify notable relevant
operators in the defect theories and use them to study the behaviour of the defect under
renormalisation group flow. 
Curing with hemlock: escaping the swampland using instabilities from string theory
Authors: Souvik Banerjee, Ulf Danielsson, Suvendu Giri
Preprint number: UUITP15/21
Abstract: In this essay we will take a wonderful ride on a dark bubble with strings attached, which carries our universe out of the swampland and makes it realizable in the landscape of string theory. To find the way to the landscape, we make use of apparently hostile corners of the swampland and their instabilities.

Kinematic numerators from the worldsheet: cubic trees from labelled trees
Authors: Linghui Hou, Song He, Jintian Tian and Yong Zhang
Preprint number: UUITP14/21
Abstract: In this note we revisit the problem of explicitly computing treelevel scattering amplitudes in various theories in any dimension from worldsheet formulas. The latter are known to produce cubictree expansion of tree amplitudes with kinematic numerators automatically satisfying Jacobiidentities, once any halfintegrand on the worldsheet is reduced to logarithmic functions. We review a natural class of worldsheet functions called “Cayley functions”, which are in onetoone correspondence with labelled trees, and natural expansions of known halfintegrands onto them with coefficients that are particularly compact building blocks of kinematic numerators. We present a general formula expressing the kinematic numerator of any cubic tree as a linear combination of these coefficients of labelled trees, including the usual combination in terms of master numerators as a special case. Our results provide an efficient algorithm, which is implemented in a Mathematica package, for computing tree amplitudes in nonlinear sigma model, special Galileon,YangMillsscalar, EinsteinYangMills, DiracBornInfeld and so on.

Generalized Vanishing Theorems for Yukawa Couplings in Heterotic Compactifications
Authors: Lara B. Anderson, James Gray, Magdalena Larfors, Matthew Magill, Robin Schneider
Preprint number: UUITP13/21
Abstract: Heterotic compactifications on CalabiYau threefolds frequently exhibit textures of vanishing Yukawa couplings in their low energy description. The vanishing of these couplings is often not enforced by any obvious symmetry and appears to be topological in nature. Recent results in the literature used differential geometric methods to explain the origin of some of this structure. A vanishing theorem was given which showed that the effect could be attributed, in part, to the embedding of the CalabiYau manifolds of interest inside higher dimensional ambient spaces, if the gauge bundles involved descended from vector bundles on those larger manifolds. In this paper, we utilize an algebrogeometric approach to provide an alternative derivation of some of these results, and are thus able to generalize them to a much wider arena than has been considered before. For example, we consider cases where the vector bundles of interest do not descend from bundles on the ambient space. In such a manner we are able to highlight the ubiquity with which textures of vanishing Yukawa couplings can be expected to arise in heterotic compactifications, with multiple different constraints arising from a plethora of different geometric features associated to the gauge bundle.

Playing with the index of Mtheory
Authors: Michele del Zotto, Nikita Nekrasov, Nicolo Piazzalunga, Maxim Zabzine
Preprint number: UUITP12/21
Abstract: Motivated by Mtheory, we study rank n Ktheoretic DonaldsonThomas theory on a toric threefold X. In the presence of compact fourcycles, we discuss how to include the contribution of D4branes wrapping them. Combining this with a simple assumption on the (in)dependence on Coulomb moduli in the 7d theory, we show that the partition function factorizes and, when X is CalabiYau and it admits an ADE ruling, it reproduces the 5d master formula for the geometrically engineered theory on A(n1) ALE space, thus extending the usual geometric engineering dictionary to n>1. We finally speculate about implications for instanton counting on TaubNUT.

Nonflat elliptic fourfolds, threeform cohomology and strongly coupled theories in four dimensions
Authors: PaulKonstantin Oehlmann
Preprint number: UUITP11/21
Abstract: In this note we consider smooth elliptic CalabiYau fourfolds whose fiber ceases to be flat over compact Riemann surfaces of genus g in the base. These nonflat fibers contribute Kähler moduli to the fourfold but also add to the threeform cohomology for g>0. In F/Mtheory these sectors are to be interpreted as compactifications of six/five dimensional N=(1,0) superconformal matter theories. The threeform cohomology leads to additional chiral singlets proportional to the dimension of five dimensional Coulomb branch of those sectors. We construct explicit examples for Estring theories as well as higher rank cases. For the Estring theories we further investigate conifold transitions that remove those nonflat fibers. First, we show how nonflat fibers can be deformed from curves down to isolated points in the base. This removes the chiral singlet of the threeforms and leads to nonperturbative fourpoint couplings among matter fields which can be understood as remnants of the former Estring. Alternatively, the nonflat fibers can be avoided by performing birational base changes, analogous to 6D tensor branches. For compact bases these transitions alternate all Hodge numbers but leave the Euler number invariant.

Exploring the Landscape for Soft Theorems of Nonlinear Sigma Models
Authors: Laurentiu Rodina, Zhewei Yin
Preprint number: UUITP10/21
Abstract: We generalize soft theorems of the nonlinear sigma model beyond the O(p^2) amplitudes and the coset of SU(N)×SU(N)/SU(N). We first discuss the flavor ordering of the amplitudes for the NambuGoldstone bosons of a general symmetry group representation, so that we can reinterpret the known O(p^2) single soft theorem for SU(N)×SU(N)/SU(N) in the context of a general group representation. We then investigate the special case of the fundamental representation of SO(N), where a special flavor ordering of the "pair basis" is available. We provide novel amplitude relations and a CachazoHeYuan formula for such a basis, and derive the corresponding single soft theorem. Next, we extend the single soft theorem for a general group representation to O(p^4), where for at least two specific choices of the O(p^4) operators, the leading nonvanishing pieces can be interpreted as new extended theory amplitudes involving biadjoint scalars, and the corresponding soft factors are the same as at O(p^2). Finally, we compute the general formula for the double soft theorem, valid to all derivative orders, where the leading part in the soft momenta is fixed by the O(p^2) Lagrangian, while any possible corrections to the subleading part are determined by the O(p^4) Lagrangian alone. Higher order terms in the derivative expansion do not contribute any new corrections to the double soft theorem.

Virasoro constraints revisited
Authors: Luca Cassia, Rebecca Lodin and Maxim Zabzine
Preprint number: UUITP09/21
Abstract: We revisit the Virasoro constraints and explore the relation to the Hirota bilinear equations. We furthermore investigate and provide the solution to nonhomogeneous Virasoro constraints, namely those coming from matrix models whose domain of integration has boundaries. In particular, we provide the example of Hermitean matrices with positive eigenvalues in which case one can find a solution by induction on the rank of the matrix model.

Coaction and doublecopy properties of configurationspace integrals at genus zero
Authors: Ruth Britto, Sebastian Mizera, Carlos Rodriguez, Oliver Schlotterer
Preprint number: UUITP08/21
Abstract: We investigate configurationspace integrals over punctured Riemann spheres from the viewpoint of the motivic Galois coaction and doublecopy structures generalizing the KawaiLewellenTye relations in string theory. For this purpose, explicit bases of twisted cycles and cocycles are worked out whose orthonormality simplifies the coaction. We present methods to efficiently perform and organize the expansions of configurationspace integrals in the inverse string tension alpha' or the dimensionalregularization parameter epsilon. Generatingfunction techniques open up a new perspective on the coaction of multiple polylogarithms in any number of variables and analytic continuations in the unintegrated punctures. We present a compact recursion for a generalized KLT kernel and discuss its origin from intersection numbers of Stasheff polytopes and its implications for correlation functions of twodimensional conformal field theories. We find a nontrivial example of correlation functions in (p,2) minimal models, which can be normalized to become uniformly transcendental in the p > \infty limit.

Fusion of conformal defects in four dimensions
Authors: Alexander Söderberg
Preprint number: UUITP07/21
Abstract: We consider two conformal defects close to each other in a free theory, and study what happens as the distance between them goes to zero. This limit is the same as zooming out, and the two defects have fused to another defect. As we zoom in we find a nonconformal effective action for the fused defect. Among other things this means that we cannot in general decompose the twopoint correlator of two defects in terms of other conformal defects. We prove the fusion using the path integral formalism by treating the defects as sources for a scalar in the bulk.

Almost contact structures on manifolds with a G2 structure
Authors: Xenia de la Ossa, Magdalena Larfors, Matthew Magill
Preprint number: UUITP06/21
Abstract: We review the construction of almost contact metric (three) structures on manifolds with a G2 structure. These are of interest for certain supersymmetric configurations in string and Mtheory. We compute the torsion of the SU(3) structure associated to an ACMS and apply these computations to heterotic G2 systems and supersymmetry enhancement. We initiate the study of the space of ACM3Ss, which is an infinite dimensional space with a local product structure and interesting topological features. Tantalising links between ACM3Ss and associative and coassociative submanifolds are observed.

Dark bubbles and black holes
Authors: Souvik Banerjee, Ulf Danielsson, Suvendu Giri
Preprint number: UUITP05/21
Abstract: In this paper we study shells of matter and black holes on the expanding bubbles realizing de Sitter space, that were proposed in arXiv:1807.01570. The explicit solutions that we find for the black holes, can also be used to construct RandallSundrum braneworld black holes in four dimensions.

Exploring SU(N) adjoint correlators in 3d
Authors: Andrea Manenti, Alessandro Vichi
Preprint number: UUITP04/21
Abstract: We use numerical bootstrap techniques to study correlation functions of scalars transforming in the adjoint representation of SU(N). We obtain upper bounds on operator dimensions for all the relevant representations and several values of $N$. We discover several families of kinks, which do not correspond to any known model and we discuss possible candidates. We then specialize to the case N=3,4, which has been conjectured to describe a phase transition respectively in the non compact complex projective space NCCP^2 and the antiferromagnetic complex projective model ACP^3. Lattice simulations provide strong evidence for the existence of a second order phase transition, while an effective field theory approach does not predict any fixed point. We identify a set of assumptions that constrain operator dimensions to a closed region overlapping with the lattice prediction.

Radiation Reaction from Soft Theorems
Authors: Paolo Di Vecchia, Carlo Heissenberg, Rodolfo Russo, Gabriele Veneziano
Preprint number: UUITP03/21
Abstract: Radiation reaction (RR) terms at the third postMinkowskian (3PM) order have recently been found to be instrumental in restoring smooth continuity between the nonrelativistic, relativistic, and ultrarelativistic (including the massless) regimes. Here we propose a new and intriguing connection between RR and soft (bremsstrahlung) theorems which shortcircuits the more involved conventional loop computations. Although first noticed in the context of the maximally supersymmetric theory, unitarity and analyticity arguments support the general validity of this 3PMorder connection that we apply, in particular, to Einstein's gravity and to its JordanBransDicke extension. In the former case we find full agreement with a recent result by Damour obtained through a very different reasoning.

Cosmic eggs to relax the cosmological constant
Authors: Thomas Hertog, Rob Tielemans, Thomas van Riet
Preprint number: UUITP02/21
Abstract: In theories with extra dimensions, the cosmological hierarchy problem can be thought of as the unnaturally large radius of the observable universe in KaluzaKlein units. We sketch a dynamical mechanism that relaxes this. In the early universe scenario we propose, three large spatial dimensions arise through tunneling from a 'cosmic egg', an effectively onedimensional configuration with all spatial dimensions compact and of comparable, small size. If the string landscape is dominated by lowdimensional compactifications, cosmic eggs would be natural initial conditions for cosmology. A quantum cosmological treatment of a toy model egg predicts that, in a variant of the HartleHawking state, cosmic eggs break to form higher dimensional universes with a small, but positive cosmological constant or quintessence energy. Hence cosmic egg cosmology yields a scenario in which the seemingly unnaturally small observed value of the vacuum energy can arise from natural initial conditions.

Inozemtsev system as SeibergWitten integrable system
Authors: Philip Argyres, Oleg Chalykh, Yongchao Lu
Preprint number: UUITP01/21
Abstract: In this work we establish that the Inozemtsev system is the SeibergWitten integrable system encoding the Coulomb branch physics of 4d \cN=2 USp(2N) gauge theory with four fundamental and (for N≥2) one antisymmetric tensor hypermultiplets. We describe the transformation from the spectral curves and canonical oneform of the Inozemtsev system in the N=1 and N=2 cases to the SeibergWitten curves and differentials explicitly, along with the explicit matching of the modulus of the elliptic curve of spectral parameters to the gauge coupling of the field theory, and of the couplings of the Inozemtsev system to the field theory mass parameters. This result is a particular instance of a more general correspondence between crystallographic elliptic CalogeroMoser systems with SeibergWitten integrable systems, which will be explored in future work.