Screening in two-dimensional gauge theories

We analyze the problem of screening in 1+1 dimensional gauge theories. Using QED2 as a warm-up for the non-abelian models we show the mechanism of the string breaking, in particular the vanishing overlap of the Wilson loops to the broken-string ground state that has been conjectured in higher-dimensional analyses. We attempt to extend our analysis to non-integer charges in the quenched and unquenched cases, in pursuit of the numerical check of a renowned result for the string tension between arbitrarily-charged fermions in the massive Schwinger model.Comment: 7 pages, 4 figures, proceedings of the XXX International Symposium on Lattice Field Theory, Cairns, Australi

Preliminary study of two-dimensional SU(N) Yang-Mills theory with adjoint matter by Hybrid Monte Carlo approach

Two-dimensional non-abelian quantum field models provide a useful laboratory for analytic and numerical investigations of quantum theories with gauge symmetry. They can exhibit various features, such as charge confinement, which are known from D=4 theories like QCD. Several analytic predictions concerning the spectra of two-dimensional systems with adjoint matter were postulated and numerical results were obtained using Discrete Light Cone Quantization techniques, however none of them has been checked via Monte Carlo simulations. In this Letter we present two such models which are particularly interesting from the physical point of view and discuss first numerical results.Comment: 7 pages, proceedings of The XXIX International Symposium on Lattice Field Theory, Squaw Valley, Lake Tahoe, Californi

Wilson loops with arbitrary charges

We discuss how to implement, in lattice gauge theories, external charges which are not commensurate with an elementary gauge coupling. It is shown that an arbitrary, real power of a standard Wilson loop (or Polyakov line) can be defined and consistently computed in lattice formulation of non-abelian, two dimensional gauge theories. However, such an observable can excite quantum states with integer fluxes only. Since the non-integer fluxes are not in the spectrum of the theory they cannot be created, no matter which observable is chosen. Also the continuum limit of above averages does not exist unless the powers in question are in fact integer. On the other hand, a new continuum limit exists, which is rather intuitive, and where above observables make perfect sense and lead to the string tension proportional to the square of arbitrary (non necessary commensurate with gauge coupling) charge.Comment: 9 pages, 3 figure

HQET form factors for Bs→KℓνB_s\to K\ell\nu decays beyond leading order

We compute semi-leptonic $B_s$ decay form factors using Heavy Quark Effective Theory on the lattice. To obtain good control of the $1/m_b$ expansion, one has to take into account not only the leading static order but also the terms arising at $O(1/m_b)$: kinetic, spin and current insertions. We show results for these terms calculated through the ratio method, using our prior results for the static order. After combining them with non-perturbative HQET parameters they can be continuum-extrapolated to give the QCD form factor correct up to $O(1/m_b^2)$ corrections and without $O(\alpha_s(m_b)^n)$ corrections.Comment: 7 pages, 4 figures. Proceedings of the 35th International Symposium on Lattice Field Theory, 18-24 June 2017, Granada, Spain; v2: small corrections, published versio

Glueball masses in 2+1 dimensional SU(N) gauge theories with twisted boundary conditions

We analyze 2+1 dimensional Yang-Mills theory regularized on a lattice with twisted boundary conditions in the spatial directions. In previous work it was shown that the observables in the non-zero electric flux sectors obey the so-called $x$-scaling, i.e. depend only on the dimensionless variable $x\propto NL/b$ and the angle $\tilde\theta$ given by the parameters of the twist ($L$ being the length of the spatial torus and $b$ the inverse 't Hooft coupling). It is conjectured that this scaling is obeyed by all physical quantities. In this work we extend the previous analyses to the zero electric flux (glueball) sector. We study the mass of the lightest scalar glueball in two theories with different $N$ but matching $x$ and $\tilde\theta$ in a wide range of couplings from the perturbative small-volume regime to the non-perturbative one. We find that the results are consistent with the $x$-scaling hypothesis.Comment: 7 pages, contribution to the 32nd International Symposium on Lattice Field Theory, 23-28 June, 2014. Columbia University New York, NY; v2: references added, minor changes; PoS(LATTICE2014)05

First passage times for subordinate Brownian motions

Let X_t be a subordinate Brownian motion, and suppose that the Levy measure of the underlying subordinator has completely monotone density. Under very mild conditions, we find integral formulae for the tail distribution P(\tau_x > t) of first passage times \tau_x through a barrier at x > 0, and its derivatives in t. As a corollary, we examine the asymptotic behaviour of P(\tau_x > t) and its t-derivatives, either as t goes to infinity or x goes to 0.Comment: 24 pages, 1 figur