Registration Room: Higgs Centre Seminar Room (4305)

Welcome

• Nils Hermansson-Truedsson (University of Edinburgh)

Room: Higgs Centre Seminar Room (4305)

Super Yang-Mills on the lattice in the large number of colours limit

• Benjamin Jaeger (University of Southern Denmark)

Room: Higgs Centre Seminar Room (4305)

Progress understanding weakly-coupled phase transitions with lattice simulations

• Oliver Gould (University of Nottingham)

Room: Higgs Centre Seminar Room (4305) It is reassuring to be able to get the same answer with two different methods, and indicates that we really understand the relevant physics. On the other hand, when two methods don't agree, at least one of them must be wrong. In the study of apparently weakly-coupled phase transitions there have been rather mixed results in matching lattice simulations against perturbation theory, suggesting that in places our understanding is lacking. In this talk, I'll present some overview of this saga, together with recent progress for some simple models.

Stationary nucleation rates for early universe phase transitions and analog systems

• Joonas Hirvonen (University of Nottingham)

Room: Higgs Centre Seminar Room (4305) First-order phase transitions in the early universe may provide a pathway for studying beyond-the-Standard-Model physics through observing a gravitational wave background, and table-top experiments allow for testing our theories of nucleation. Nucleation rates are often modeled with the assumption that the metastable phase stays in equilibrium throughout the majority of the transition, which is known to be incomplete to at least some degree. In this talk, we discuss a framework for going beyond the assumption and performing lattice simulations to find the appropriate stationary nucleation rate. We will also highlight results from 1+1-dimensional lattice simulations: indications of the equilibrium assumption being quite good for early universe due to large exponential suppression, the stationary rate potentially being much below the equilibrium one in table-top experiments and finite-size effects possibly destabilizing the stationary rate altogether. These results highlight the importance of understanding the thermalization of the nucleating degrees of freedom, since it is an important component in determining the stationary nucleation rate.

Domain-wall-seeded bubble nucleation on the lattice

• Jaakko Hällfors (University of Helsinki)

Room: Higgs Centre Seminar Room (4305) First-order phase transitions are common in many beyond the Standard Model theories. Nucleating transitions are particularly interesting, since they leave behind a gravitational wave background (GWB) that could be observable in many near-future experiments. The nucleation rate determines how fast the transition completes and is needed for precision predictions of the GWB. Typically, the metastable system is assumed to be spatially homogeneous. In contrast, in the seeded case the nucleation probability is locally enhanced by some impurity in the system, such as a topological defect. We consider a system of two scalar fields in two spatial dimensions with a domain wall as the impurity. The scenario is that of a two-step transition in which the first transition leaves behind a system of domain walls that in turn seed the second transition to the true vacuum. For very slow nucleation the rate is estimated using multicanonical MCMC to determine the probability of critical bubble configurations. For faster nucleation, as in our case, we can simply evolve the system in time and wait for the nucleation to occur. We compare the simulation results to analytic estimates computed in a dimensionally reduced effective field theory living on the domain wall and find good agreement.

Bubble nucleation in SU(8) (de)confinement transition

• Riikka Seppä (University of Helsinki)

Room: Higgs Centre Seminar Room (4305) Strongly coupled theories which can undergo a thermal first order phase transition are of phenomenological interest, for example as dark matter candidates. Furthermore, they are potential sources of a stochastic gravitational wave background. As a prototype for models with a confinement transition, we study the deconfinement transition of SU(8) pure gauge model with 4D multicanonical lattice simulations. We present results for the critical bubble probability and compare it to results from thin wall calculations. We also compare the effectiveness of different lattice pseudo-order parameters at identifying the bubble configurations and discuss whether our 'critical' bubble configurations are truly critical.

Generalizable Equivariant Diffusion Models for Non-Abelian Lattice Gauge Theory

• Diaa Eddin Habibi (Swansea University)

Room: Higgs Centre Seminar Room (4305) In this talk, I will present our work on gauge equivariant diffusion models for simulating non-Abelian lattice gauge theories. Using the Metropolis-adjusted annealed Langevin algorithm (MAALA) together with lattice gauge equivariant convolutional neural networks (L-CNNs), we accurately reproduce the physics of two-dimensional U(2) and SU(2) gauge theories. Trained on a single Monte Carlo ensemble, our models generalise well to larger lattice sizes and stronger couplings with minimal accuracy loss. I will present results for Wilson loops and the topological susceptibility, demonstrating that diffusion models are a promising approach for lattice gauge theory beyond the Abelian case.

Stein-optimal transport for the Signal-to-Noise Problem

• Pietro Butti (SDU - University of Southern Denmark)

Room: Higgs Centre Seminar Room (4305) We address the signal-to-noise problem in lattice field theory by framing it as a task in variance-optimal transport. The degradation of the signal-to-noise ratio is shown to result from poor overlap between the configuration distribution and the target distribution in a source reweighting scheme. We introduce an infinitesimal transport map and derive a perturbative expansion of the KL divergence to determine the optimal transport field. This expansion reveals a connection to Stein geometry and allows us to recast the optimisation problem as a Poisson equation. A formal solution is provided using a stochastic method, thereby establishing a link to linear response theory. Finally, we present preliminary numerical results for scalar lattice field theories.

Fighting critical slowing down with Neural Enhanced Out-of-Equilibrium Sampling.

• Elia Cellini (University of Edinburgh)

Room: Higgs Centre Seminar Room (4305) Critical slowing down is the well-known phenomenon whereby the integrated autocorrelation time of Markov Chain Monte Carlo simulations, and therefore the computational cost, grows rapidly as one approaches the continuum limit. This effect is particularly severe for topological observables in non-Abelian gauge theories. In this talk, I will present Stochastic Normalizing Flows (SNFs), hybrid algorithms in which non-equilibrium Markov Chain Monte Carlo algorithms are enhanced with normalizing flows, a class of deep generative models. I will show that SNFs significantly mitigate topological freezing in $3+1$ dimensional SU(3) gauge theory, while exhibiting favorable scaling with the lattice volume. I will then introduce a novel neural enhanced out-of-equilibrium approach for sampling lattice field theory based on Langevin dynamics. I will discuss the conceptual advantages of this framework and present preliminary results for lattice non-linear $\sigma$ models.

Scaling of Annealing Methods for Lattice Field Theory Sampling

• Satria Widyanto (University of Edinburgh)

Room: Higgs Centre Seminar Room (4305) -

Lattice QCD form factors for radiative leptonic decays of heavy mesons

• Teseo San Jose (University of Edinburgh)

Room: Higgs Centre Seminar Room (4305) We report our ongoing lattice QCD study of radiative leptonic decays of the pseudoscalar mesons $D$, $D_s$, $B$, and $B_c \to \ell \nu_\ell \gamma$. We carry out our analysis on a single JLQCD ensemble with lattice spacing $a=0.044~\text{fm}$. This work is a step towards a complete QCD+QED lattice calculation of these modes, aimed at reducing theoretical uncertainties in the extraction of $|V_{cd}|$ and $|V_{cs}|$ and providing first-principles estimates of the corresponding form factors in the $B$ sector.

Laplace Filters to optimise correlator fits

• J Tobias Tsang (CERN)

Room: Higgs Centre Seminar Room (4305) TBC

Lattice calculation of s- to d-quark transitions in the Standard Model

• Vera Guelpers

Room: Higgs Centre Seminar Room (4305) The transition of a strange to a down quark requires a flavour changing neutral current (FCNC) which is forbidden at tree level in the Standard Model. Consequentely, processes involving such transition are sensitive to any potential physics beyond the standard model including a FCNC. In this talk, I will present the status of lattice calculations for two such decays: the rare Kaon decay $K^+ \to \pi^+ \ell^+ \ell^-$, and the rare Hyperon decay $\Sigma^+ \to p \ell^+ \ell^-$.

Approaching a prediction for the inclusive semileptonic $B_s \to X_c$ decay rate using lattice QCD

• Ahmed Elgaziari (University of Southampton)

Room: Higgs Centre Seminar Room (4305) We discuss the calculation of the inclusive semileptonic decay for the process $B_s \to X_c \, l\nu_l$ using lattice QCD. Such a calculation could be decisive in understanding the CKM matrix puzzle: the long-standing tension between inclusive and exclusive determinations of the CKM matrix element, $V_{cb}$. This talk will be an overview of the calculation using Chebyshev reconstructions. We will go on to explore the steps towards a phenomenological prediction for the inclusive decay rate of the $B_s$. These steps will include analysing systematic effects associated with reconstructions as well as those associated with infinite and continuum limits.

Three-loop hadronic vacuum polarization

• Mattias Sjö (CPT Marseille)

Room: Higgs Centre Seminar Room (4305) The three-loop calculation of the hadronic vacuum polarization in chiral perturbation theory, which I presented at the last Nordic Lattice Meeting, is now complete. I will demonstrate the full result, with particular attention given to the pieces that had not yet fallen into place last year. I will also show some first glimpses into the corresponding calculation in finite volume, which when complete will be a highly precise correction to lattice calculations.

Color electric field correlators for diffusion of heavy quarkonia

• Viljami Leino (QTC - Univeristy of Southern Denmark)

Room: Higgs Centre Seminar Room (4305) The diffusion of a heavy quarkonium in a strongly interacting plasma can be described, using a nonrelativistic effective field theory formalism, in terms of transport coefficients related to the correlators of color electric fields connected by adjoint Wilson lines. These transport coefficients are important for the calculation of quarkonia suppression in the plasma. We present a lattice calculation of these correlators with the gradient flow for the SU(3) gluon plasma and extract the relevant transport coefficients.

Weak and Higgs physics from the lattice

• Sofie Martins (University of Graz)

Room: Higgs Centre Seminar Room (4305) The manifestly gauge-invariant and non-perturbatively complete lattice formulation of the weak interactions and the Brout-Englert-Higgs effect is connected to the usual perturbative description in phenomenology via the Fröhlich-Morchio-Strocchi mechanism. However, slight differences between the two have been observed, which can potentially be accounted for by augmenting perturbation theory. We report on our ongoing lattice investigations of these additional effects using a setup with two generations of leptons coupled vectorially to the gauge-Higgs system. We explore the spectrum, inner structure in terms of weak (quasi-)PDFs, and spectral functions of the system to eventually compare cross sections to experimental results.

Quantum Computing of Lattice Gauge Theories is simpler with Non-Compact Variable!

• Emanuele Mendicelli (University of Liverpool)

Room: Higgs Centre Seminar Room (4305) Simulating lattice gauge theories on quantum computers presents significant challenges, motivating the development of novel theoretical frameworks. The orbifold lattice formulation provides a scalable approach for quantum simulations of lattice gauge theories. Quantum circuits for this framework can be explicitly constructed, with computational complexity scaling polynomially with the number of qubits. Monte Carlo simulations (arXiv:2604.15132) demonstrate that the orbifold lattice for SU(2) in (2+1) dimensions recovers the Kogut–Susskind formulation in the large scalar mass limit.

Benchmarking Modern HPC Architectures with Lattice QCD

• Ryan Hill (University of Edinburgh)

Room: Higgs Centre Seminar Room (4305) tbc

Thermodynamics from Entanglement Entropy

• Aatu Rajala (University of Helsinki)

Room: Higgs Centre Seminar Room (4305) Entanglement is a defining property of quantum physics and provides a natural way to characterize correlations. Despite some inherent difficulties, there has been considerable advancement in lattice evaluations of entanglement measures, such as entanglement entropy (EE). In this talk, I will present our argument that, at large subregions, the derivative of EE with respect to the size of the entangling region equals the thermal entropy density. We provide validation for these claims from our lattice computations in the three-dimensional O(4) model at finite chemical potential by showing that in the corresponding limit, the EE derivative satisfies the same Maxwell relation as the thermal entropy density. These results pave the way for extracting thermodynamics from entanglement data in general QFTs.

Order-Order Interface Tension in SU(N) Gauge Theory

• Aaron Haarti (University of Helsinki)

Room: Higgs Centre Seminar Room (4305) For the confined phase of pure SU(N) gauge theory, we use a twisted boundary condition to produce two ordered phases simultaneously. Between these two ordered phases there naturally lies an order-order (o-o) interface, for which we evaluate the surface tension by calculating the difference in free energy of the twisted and non-twisted lattices. To accurately measure the first-order phase transition region, we employ multicanonical sampling. With these measurements, we draw conclusions of the finite volume effects of the method and the perfect wetting hypothesis.

Measuring deconfined-deconfined interface tensions in SU(N) gauge theory with the capillary wave method

• Tobias Rindlisbacher (University of Helsinki)

Room: Higgs Centre Seminar Room (4305) We previously applied the mixed phase / capillary wave method to determine the interface tension of the confined-deconfined (CD) phase interface in pure SU(N) gauge theory (N>3) at $T=T_c$. In this work we show how the method can be extended to the study of deconfined-deconfined (DD) interfaces for $T>T_c$, i.e., to measure the interface tension of interfaces between distinct deconfined phases (different $Z_N$-centers). These DD interface tensions depend in general on the $Z_N$-phase shift across the interface and on the temperature $T$. We map out the $T$-dependency of the different DD interface tensions in SU(4) and SU(8) to see whether they show casimir scaling for $T\gg T_c$ and whether there is perfect wetting in the limit $T\to T_c$.

Higgs Colloquium: Gravitational waves and phase transitions in the early Universe

• Kari Rummukainen (University of Helsinki)

Room: Higgs Centre Seminar Room (4305)