PaperPanorama

HEP Lattice·hep-lat

Thu·Sep 24, 2026

3 papers—2 primary·1 cross-listed

All3Primary2Cross-lists1
  1. 01

    A variational framework for variance reduction in lattice field theory

    Pietro Butti · Guilherme Catumba · Alessandro Nada · Louis Spatscheck

    The signal-to-noise problem limits the reach of many lattice calculations. We present a variational framework that recasts it as a transport problem: the loss of signal reflects a mismatch between the distribution one samples and the one needed to measure an observable, and can be reduced by transporting configurations to close that gap. The optimal transport is typically determined either through a stochastic estimator based on Langevin dynamics or by parametrising it as a normalising flow trained with automatic differentiation. We discuss how the framework brings these methods under a common variational principle and present results for scalar theories.

    hep-lat
  2. 02

    Larger physical volume and bounds on the number of matter fields in noncompact gauge theories on a lattice

    Fabrizio Palumbo

    The work was motivated by the numerical result that in a pure SU(2) gauge theory the ratio R of the effective non-compact and compact lattice spacing is larger than 1 and increasing with decreasing gauge coupling, as well as the expectation that it should further increase extending the parameter space. This means that with a noncompact regularization, at given number of lattice sites and comparable scaling, one can obtain a larger physical volume, whose importance for the control of size effects has long been known. We confirm qualitatively results and expectation by a perturbative evaluation of the effective lattice spacing in an expansion in the Plank constant of non-compact pure SU(2) and Abelian gauge theories, but we find in addition that R reaches the maximum value of sqrt(2). Including matter fields we find that R increases ( still up to sqrt(2) ) or decreases depending on the difference between the number of scalar and spinor degrees of freedom, and there are bounds on such a difference.

    hep-latcond-mat.other
  3. 03

    Fermion bag study of the two-dimensional Majorana-Hubbard model at finite hopping

    Mark Johnston · Emilie Huffman

    The two-dimensional Majorana-Hubbard model on the -flux lattice involves the most local interaction possible for a lattice with one relativistic Majorana fermion per site. It is predicted to host a Majorana semimetal, dimerized phases, and quantum-critical points with an emergent symmetry. Nonperturbative lattice calculations for this model remain a major open challenge, thus far limited to zero hopping. We present quantum Monte Carlo simulations of the model at finite hopping using Hamiltonian fermion bags, which are based on a continuous-time expansion with Boltzmann weights that are Pfaffians of a matrix with dimension set by the expansion order, and which give the sign of the weight. Sign problem severity is related to the location of zero modes in the free hopping matrix, and for couplings and it is fully removed for lattices up to at least sites. The interaction strength enhances the -charged dimerization doublet and suppresses the neutral channel, as the renormalization group predicts. Increasing the interactions also restores symmetry in the component of the dimerization correlator that is even under bond orientation exchange, but not its odd component. There is a persistent anisotropy in the odd component with the symmetry of a lattice nematic. The data is consistent with a gapless semimetal throughout the sign-problem-minimal window.

    ↳ cond-mat.str-elhep-latquant-ph