We consider quantum decoherence and entropy increase in early universe cosmology. We first study decoherence in a discrete bipartite quantum system for which a single qubit gets entangled with an environment and the entropy increase is correlated with the decay of the off-diagonal terms of the reduced density matrix. We compare this system with continuous systems relevant for cosmology for which there is a natural external intervention, corresponding to the time-dependent separation between the sub- and super-horizon infla-tionary fluctuations. We find, in this case, that the off-diagonal terms of the density matrix, in a field basis, do not decay as sometimes assumed in cosmological set-ups. Nevertheless, following a recent treatment in terms of open Effective Field Theories (EFTs), we compute the entanglement entropy for a Gaussian state and show that it actually increases monotonically ( $$\dot{S}&gt;0$$ ) during the accelerated phases ( $$\ddot{a}&gt;0$$ with $\textit{a}$($\textit{t}$) the scale factor). We generalise this result to include non-Gaussian states and briefly discuss the relevance of computing the von Neumann entropy as compared to the thermodynamic entropy.

United Kingdom

Chile

Sebastián Céspedes

United States

Senarath Alwis

not found

Fernando Quevedo

Cosmology, decoherence and the second law

We develop a framework for indirect discovery in the Standard Model Effective Field Theory (SMEFT) based on Bayesian model selection over operator subsets. We argue that SMEFT should be understood as a structured space of competing hypotheses rather than a single high-dimensional model, with each operator subset corresponding to a physically distinct low-energy realisation of new dynamics. Bayesian inference is applied at the level of model space itself, assigning posterior probabilities to operator subsets and marginal inclusion probabilities to individual operators. A genetic algorithm efficiently navigates the high-dimensional discrete model space, concentrating evaluations in the high-posterior region, while the Bayesian Information Criterion provides a tractable approximation to the Bayesian evidence. We apply this framework to a dataset comprising electroweak precision observables from LEP and Higgs, top-quark, and diboson measurements from LHC Run 2, at both linear and quadratic order in the Wilson coefficients, with one-loop renormalisation group evolution systematically included. The analysis finds no statistically significant evidence for any departure from the SM, and demonstrates that Bayesian Model Average posteriors on Wilson coefficients carry substantially improved characterisation potential compared to traditional global fits. The operator correlation matrix encodes the relational structure of the model posterior, identifying operator pairs that co-appear in high-posterior models and flat directions where additional measurements would be most valuable. The sensitivity of all results to the choice of matching scale $\textit{μ}$ is assessed, and its promotion to a continuous parameter of inference is identified as a natural extension of the framework.

Spain

Luca Mantani

Exploring the SMEFT landscape: Bayesian model selection for indirect discovery

We present a method to obtain analytic results in terms of multiple polylogarithms for one-loop triangle, box and pentagon integrals depending on an arbitrary number of scales and to any desired order in the Laurent expansion in the dimensional regulator $\textit{ε}$. Our method leverages the fact that for $\textit{ε}$ = 0 one-loop integrals compute volumes of simplices in hyperbolic spaces, which can always be evaluated in terms of polylogarithms using an algorithm recently introduced in pure mathematics. The higher orders in $\textit{ε}$ can then be expressed as a one-fold integral involving the result for $\textit{ε}$ = 0. Remarkably, we find that for up to five external legs, all integrals can be evaluated algorithmically in terms of polylogarithms using direct integration techniques, which, in particular, requires us to rationalise all appearing square roots. We also discuss how we can use the connection to hyperbolic geometry to perform the analytic continuation from the Euclidean region to other kinematic regions.

Germany

Claude Duhr

Paul Mork

Analytic results for one-loop integrals in dimensional regularisation

We construct the 𝒩 = 4 supersymmetric completion of the recently proposed single-minus gluon amplitudes in (2$\textit{,}$ 2) signature, which are nonvanishing for all multiplicities on a half-collinear kinematic locus. The superamplitude factorises into a permutation-invariant measure ∆ with uniform little-group weight that imposes the half-collinearity constraint, a piecewise constant stripped amplitude $${\widetilde{A}}_{1\dots n}$$ that is helicity blind and dual conformal invariant, and (super)momentum conservation delta functions. For $\textit{n}$ = 3, our superamplitude reduces to the known $$\overline{\text{M}\text{H}\text{V} }$$ superamplitude. We prove dual superconformal covariance of the $\textit{n}$-point superamplitude, and further analyse the Gr($\textit{k, n}$) Grassmannian integral at $\textit{k}$ = 1. Finally, we present the corresponding single-minus superamplitude in 𝒩 = 8 supergravity.

Andreas Brandhuber

Paolo Pichini

Gabriele Travaglini

Congkao Wen

𝒩 = 4 single-minus superamplitudes and dual superconformal symmetry

We approach a systematic investigation of the one-loop mass corrections to (super-)string massive higher-spin states. While the imaginary part of the relevant amplitudes is finite, being related to the width of the decay of the states into two lower-mass states at tree level, the real part is generally IR-divergent and needs regularization and renormalization. We mostly focus on states of the first Regge trajectory in the NS-NS sector of Type-II string theories. We explicitly derive a closed-form expression for the integral over the insertion point, relying on properties of elliptic functions and lattice sums. We then regularize the IR divergent integral over the modular parameter of the torus, applying the $\textit{iε}$-prescription in string theory. As a result we compute the desired mass corrections up to level $\textit{N}$ = 10 and analyze their behavior at increasing $\textit{N}$. Finally, we speculate on the existence of mixing among lower-spin states and conjecture that the one-loop mass matrix be governed by some random matrix theory.

Italy

Massimo Bianchi

China

Maurizio Firrotta

Lorenzo Grimaldi

One-loop mass corrections and decay widths of Type II heavy string states

We investigate the effects of D-instantons on a holographic Weyl semimetal in a top-down approach. We find that the presence of D-instantons induces a novel phase transition from a Weyl semimetal to a gapped phase, providing a new mechanism for gap formation in strongly coupled systems. By analyzing the free energy of probe D7-brane embeddings, we construct the phase diagram in terms of the fermion mass, instanton density, and temperature, measured in units of the Weyl parameter. We show that, in addition to the conventional mass-driven transition associated with band inversion, the instanton density gives rise to a qualitatively different transition whose mechanism cannot be understood within the standard Dirac picture. We compute nonlinear electric conductivities from the regularity condition at the black hole horizon and demonstrate that the two types of transitions exhibit distinct transport behavior. In particular, the instanton-induced transition leads to a gapped phase with properties that differ from the conventional insulating phase. We also discuss possible interpretations of this phase in the boundary theory and comment on its relation to nonperturbative effects in strongly interacting systems.

South Korea

Hwajin Eom

Yunseok Seo

D-instanton effects on the holographic Weyl semimetals

We study a six-dimensional SU(9) grand unified model with rank-reducing discrete boundary conditions and continuous Wilson line phases on the orbifold $\textit{T}$ $\textit{/}$ℤ . We show that the model can realize grand unification of the Standard Model gauge interactions and electroweak symmetry breaking via the Hosotani mechanism. The model has several attractive features. Two Higgs doublets arise as zero modes of the extra-dimensional components of the gauge field, and the leptons and quarks in each generation are separately embedded into two bulk multiplets, in the and representations of SU(9), respectively, without exotic matter. Furthermore, proton decay processes mediated by the gauge bosons in the bulk are absent, because the leptons and quarks belong to different bulk multiplets.

Japan

Yoshiharu Kawamura

Kentaro Kojima

Toshifumi Yamashita

SU(9) grand unified model with rank-reducing discrete boundary conditions on $\textit{T}$ 2 $\textit{/}$ℤ4

We reconsider the “fortuity” mechanism in the D1D5 CFT focusing on the K3 symmetric orbifold. Going beyond the counting of BPS states, we investigate perturbatively how the explicit form of the BPS cohomologies is modified by the twist-two deformations. We calculate the action of the supercharges in the sector ($\textit{h}$, $\textit{j}$) = (1, 0) for different values of the central charge and derive explicit expressions for the primary states. Equipped with this information, we compare some protected three-point couplings in the free and the gravity regime. We show that agreement between the two descriptions imposes non-trivial constraints on the identification of monotone and fortuitous states. In particular, we argue that the map relating theories with different values of the central charge must and can be defined so as to commute with the supercharges that define the cochain complex. We then study the three-point correlators between the fortuitous and monotone states identified in our analysis to assess whether the two sectors are dynamically decoupled. We find an explicit example of a non-vanishing coupling between two monotone and a fortuitous state, providing evidence that the two sectors are dynamically connected.

Stefano Giusto

James Inglis

Rodolfo Russo

Fortuity beyond counting: an explicit construction

We study static, spherically symmetric axion-dilaton solutions of the tree-level four-dimensional string effective action. Using the sigma-model structure of the scalar sector, we show that the full family of static, spherically symmetric and asymptotically flat solutions is obtained as the SL(2, $\textit{ℝ}$) orbit of the pure-dilaton FJNW solution, and we characterize the associated axion-dilaton charge space. We then analyze the perturbative regime of these solutions by comparing the onset of $\textit{α}$ curvature corrections with that of string-loop corrections. Finally, we apply the string-black-hole correspondence criterion to the FJNW family by evaluating the local $\textit{α}$ curvature diagnostic at the physical size $\textit{R}$ of a highly excited string state. With the normalization fixed on the Schwarzschild branch, Schwarzschild saturates the nominal $\textit{α}$ threshold at the correspondence surface, whereas every scalar-haired FJNW branch lies above it. More generally, independently of the common overall normalization within the matching prescription, every nonzero-hair branch has a larger curvature diagnostic at the correspondence surface than Schwarzschild. Away from the correspondence point, scalar-haired exteriors may remain under $\textit{α}$ control at sufficiently weak local self-gravity and may provide perturbatively controlled long-distance fields of highly excited string states whenever the local string coupling also remains weak.

E. Pavone

Scalar hair at the string-black-hole correspondence

Quantum correlation functions in supersymmetric field theories can be encoded in the Nicolai map. The infinitesimal inverse map provides their response to a change in a coupling constant through a “flow equation”. We investigate the flow in the gravitational constant $\textit{κ}$ for four-dimensional Poincaré supergravity via its superconformal formulation. By expressing the full superconformal off-shell action as a supervariation we derive a “flow operator” in the effective vierbein theory, whose exponentiation yields the gauge-invariant part of an all-order (inverse) Nicolai map for supergravity. Alas, the BRST gauge fixing adds to this functional differential flow operator a multiplicative term, which ruins its derivational property and therefore jeopardizes its connection with the Nicolai map. We argue and present an example, however, that such multiplicative flow contributions might be rewritable as derivational ones with the help of Wick’s theorem in the free effective theory where the Nicolai-transformed correlators are ultimately evaluated. At least in the Landau gauge, the supergravity flow equation is shown to be regular at $\textit{κ}$=0, allowing for a perturbative expansion around Minkowski geometry. Therewith, we have overcome two of the three obstacles met in an earlier attempt towards a Nicolai map for Poincaré supergravity. Finally, we compare with the direct on-shell construction of a Nicolai map to leading order in $\textit{κ}$.

Federico Arrighi

Saurish Khandelwal

Olaf Lechtenfeld

The coupling flow for supergravity