We study noncommutativity in open strings using the covariant phase space formalism. For tensile open strings in a constant Kalb-Ramond background, we show that the (pre)-symplectic current splits into a bulk kinetic term plus an exact boundary term, recovering the Seiberg-Witten noncommutativity parameter. We then extend the analysis to intrinsically tensionless strings. In the absence of background fields, the reduced phase space is degenerate and carries no intrinsic Poisson structure. In the presence of a constant Kalb-Ramond field, the symplectic current localises entirely on the boundary, so that the physical phase space becomes purely boundary-supported and the endpoint coordinates acquire a noncommutative Poisson algebra. Including a boundary gauge-field coupling similarly leads to a boundary symplectic form governed by the effective Born-Infeld combination on the D-brane. Our results provide a unified description of noncommutativity in both tensile and tensionless open strings.

India

Pratik Das

China

Sarthak Duary

Sourav Maji

Covariant phase space approach to noncommutativity in tensile and tensionless open strings

We compute the complete set of the leading-twist gluon and sea-quark generalized transverse momentum distributions (GTMDs) at small-$\textit{x}$, or eikonal, approximation and for vanishing skewness $\textit{ξ}$ = 0. All the gluon GTMDs become expressed in terms of the basic gluon dipole operator featuring also proton helicity-flips. Consequently, we establish universal relations between otherwise distinct GTMDs that hold in the small-$\textit{x}$ limit. The obtained results are systematically projected onto the transverse momentum dependent distributions (TMD) and the generalized parton distribution (GPD) cases, recovering known results where available. In case of sea-quarks all the GTMDs are given in terms of the gluon dipole convoluted with a hard kernel. We generalize the unpolarized sea-quark GTMD to non-zero momentum transfers and find new results for the proton helicity-flip distributions. We pay special attention to their perturbative, high transverse momentum, tails to confirm that it becomes governed by the high transverse momentum behavior of the hard kernel and are proportional to the small-$\textit{x}$ gluon GPDs. The obtained results provide guidance to the phenomenological modeling of the GTMDs but also allow for their explicit computations.

Croatia

Sanjin Benić

Yoshikazu Hagiwara

Boris Šarić

Eric Vivoda

Generalized transverse momentum distributions at small-$\textit{x}$

We study the $\textit{α}$ corrections to self-dual gravitational instantons in the context of the four-dimensional Cano-Ruipérez action, which can be obtained by the compactification of the Bergshoeff-de Roo heterotic string effective action on $${\mathbb{T}}^{6}$$ followed by a truncation and a field redefinition. We show that the metric of spaces of self-dual curvature does not receive any corrections, but their (initially trivial) dilaton and axion fields do, owing to their couplings to Gauss-Bonnet and Pontrjagin densities. We find the generic form of the corrections of the dilaton and axion fields for the Gibbons-Hawking multi-instanton solutions and their explicit form for the particular cases of the Euclidean Taub-NUT and Eguchi-Hanson spaces. We construct the boundary terms required to define a well-posed Dirichlet variational principle in the Euclidean Cano-Ruipérez theory, including the contributions associated with the Gauss-Bonnet and Pontrjagin terms. The boundary terms are normalized for asymptotically-locally-Euclidean solutions, and we evaluate with them the Euclidean action of the $\textit{α}$ -corrected Eguchi-Hanson instanton showing that the total action receives no corrections to first order in $\textit{α}$ . We also show that, at zeroth order in $\textit{α}$ , one can construct Euclidean solutions similar to the string theory D-instanton with non-trivial dilaton and axion on the background of a self-dual purely gravitational instanton which remains unmodified. We also compute the $\textit{α}$ corrections to these solutions.

Spain

José Cerdeira

Chile

Cristóbal Corral

Tomás Ortín

$\textit{α}$ ′ corrections to self-dual gravitational instantons

We consider weakly interacting massive particle (WIMP) dark matter in a Parity solution to the strong CP problem. The WIMP phenomenology can be drastically affected by the presence of Parity partners of the WIMP and electroweak gauge bosons. We focus on a Parity extension of SU(2) -doublet fermion dark matter, identify the viable parameter space, and derive the predictions of the theory. We find that the Parity symmetry breaking scale is bounded from above, with the bound given by 25–60 TeV, depending on whether or not dark matter and its Parity partner coannihilate with each other. The High-Luminosity Large Hadron Collider, future colliders, and direct and indirect detection experiments can probe the parameter space further, with correlated signal rates.

United States

Matthew Baldwin

Japan

Keisuke Harigaya

Isaac Wang

Upper bound on Parity breaking scale for doublet WIMP dark matter

A strongly coupled confining gauge theory with a non-zero vacuum angle undergoing a deconfinement to confinement phase transition is studied in the holographic gravitational description. A simplified five-dimensional setup is constructed where a bulk scalar models the effect of the vacuum angle, and the suitable boundary conditions on the ultra-violet (UV) and the infra-red (IR) boundaries are identified. The IR boundary condition is motivated by higher dimensional examples where the bulk scalar comes from a Wilson loop on a shrinking cycle. In this five-dimensional dual geometry, and in the limit of small backreaction in the infra-red, the critical temperature for the phase transition is shown to reduce quadratically with the vacuum angle, matching lattice results. The topological susceptibility has a sharp reduction across the critical temperature, also matching lattice results. The rate for the phase transition is estimated as a function of the vacuum angle, and is seen to be enhanced (reduced) when the field theory has a relevant (irrelevant) deformation at high energies. Crucially, for the irrelevant case, the confined phase can get destabilized for a range of parameters. In the context of early universe dynamics, if the vacuum angle is time-dependent, the transition history changes strongly: the deconfined phase can last till much lower temperatures than naively expected, and one can trigger a transition to the confined phase by a change in the vacuum angle, thus providing a controlled way to generate supercooling. As a phenomenological application, the peak frequency and the power of resulting gravitational wave signal from bubble collisions can be modified, potentially affecting their visibility in detectors. Possible generalizations of the scenario are discussed.

Rashmish Mishra

Confinement in holographic theories at finite theta

We study anomalies in family unification models within the framework of the bordism classification of invertible field theories. These models are based on four-dimensional $$ \mathcal{N} $$ = 1 supersymmetric nonlinear sigma models, in which the three generations of quarks and leptons arise as superpartners of the sigma model fields. We focus on models whose target spaces are constructed from the exceptional group $\textit{E}$ and its subgroups. For the consistency of the theory, sigma model anomalies must be cancelled. We show the absence of global sigma model anomalies, which are encoded in the torsion part of the relevant bordism groups, by explicitly computing these groups using the Atiyah-Hirzebruch spectral sequence. In constructing family unification models, symmetries acting on the coset spaces are gauged, which may introduce additional anomalies. We identify the relevant bordism groups in this setting and demonstrate that no global anomalies arise when the isotropy subgroup of the coset space is gauged.

Tsubasa Sugeno

Hiroki Wada

Anomalies in family unification models from bordism classification

We investigate the divergent perturbative series of correlation functions for a massless, self-interacting scalar field in de Sitter space. First, we use our previously proposed method of autonomous equations to obtain finite time-dependent functions, and show that these functions approximate the time evolution of the correlation functions of the stochastic approach reasonably well. Second, we apply the technique of autonomous equations to the Borel–Le Roy transforms of correlation functions, and use solutions of these equations to perform Borel resummation. The results match the time evolution obtained in the stochastic picture substantially better. In addition, we propose an alternative method for extracting perturbative coefficients and provide a new derivation of our autonomous equation by truncating a system of Schwinger–Dyson-type differential equations.

Italy

Alexander Kamenshchik

Russia

Polina Petriakova

Armenia

Tereza Vardanyan

Taming the infrared in de Sitter space: autonomous equations, stochastic approach, and Borel resummation

Final states comprising two or more top quarks are important search channels at the Large Hadron Collider for scalar particles predicted in models of physics beyond the Standard Model. While the di-top final state profits from a higher signal cross section, it can be subject to intricate interference patterns. Besides the interference with the large QCD background, in case of the presence of more than one high-mass scalar also large signal–signal interference contributions can occur. We show that in such scenarios it is crucial to account for loop-level mixing for obtaining accurate exclusion bounds. We demonstrate how the interference patterns can obscure the interpretation of possible deviations from the Standard Model expectations. We show that the four-top final state, while giving rise to a smaller signal cross section, provides important complementary information due to its much smaller signal–background interference contributions. Thus, the results obtained from the four-top final state can be instrumental for pinpointing the underlying new physics scenario.

Germany

Henning Bahl

Philipp Gadow

Romal Kumar

Krisztian Peters

Cyprus

Panagiotis Stylianou

Georg Weiglein

Complementarity of di-top and four-top searches in interpreting possible signals of new physics

Nobuhiro Maekawa

Kei Shibata

Masato Yamanaka

Erratum: Thermal leptogenesis in $\textit{SO}$(10) $\textit{× U}$(1) $\textit{A}$ SUSY GUT

For generic theories of nonlinear electrodynamics (NLED) we investigate the implications of (a)causality on spherically-symmetric solutions of the Einstein-NLED equations that are asymptotic to a Reissner-Nordström (RN) spacetime. Equal-charge dyonic RN black holes are shown to be exact, but unstable, solutions of (acausal) “Born-type” theories. For $\textit{all causal theories}$ it is shown that the metric is singular at the centre of symmetry and that it has at most two Killing horizons, implying at most three “phases”: RN-like or S(chwarzschild)-like black holes, and naked timelike singularities. For extreme RN-like black holes, including dyons, we give simple proofs of monotonicity conditions that imply a reduction of mass and entropy due to NLED interactions. We find that causality allows four qualitatively different phase-diagrams. One of the two with finite electromagnetic energy ℰ is the previously studied Born-Infeld-type, for which the zero-entropy limit of a “small-charge” S-like black hole is a naked timelike singularity of mass $\textit{M}$ = ℰ ; we show that the spacetime geometry of this “Born particle” is that of the Bariola-Vilenkin global monopole.

Jorge Russo

United Kingdom

Paul Townsend

Black holes and causal nonlinear electrodynamics