Publications 2021

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.