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Sz. Borsanyi

Publications and source records attributed to Sz. Borsanyi.

At least 19 recordsLinked to original sources
arXiv2026

Hybrid calculation of hadronic vacuum polarization in muon g-2 to 0.48\%

We present a new lattice QCD calculation of the leading order hadronic vacuum polarization (LO-HVP) contribution to the muon anomalous magnetic moment $a_μ$. We reduce uncertainties compared to our earlier computation arXiv:2002.12347 by a factor of 1.6. We perform simulations on finer lattices allowing for an even more accurate continuum extrapolation. We also include a small, long-distance contribution obtained using input from experiments in a low-energy regime where they all agree. Combined with other standard model contributions our result, $a_μ^{LO-HVP}=715.1(2.5)(2.3)[3.4] \times 10^{-10}$, leads to a prediction that differs from the recent measurement of $a_μ$ by only 0.5 standard deviations. This provides a remarkable validation of the standard model to 11 digits.

hep-lat↗
arXiv2022

Topological features of the deconfinement transition

The first order transition between the confining and the center symmetry breaking phases of the SU(3) Yang-Mills theory is marked by discontinuities in various thermodynamics functions, such as the energy density or the value of the Polyakov loop. We investigate the non-analytical behaviour of the topological susceptibility and its higher cumulant around the transition temperature and make the connection to the curvature of the phase diagram in the $T-θ$ plane and to the latent heat.

hep-lat↗
arXiv2022

QED and strong isospin corrections in the hadronic vacuum polarization contribution to the anomalous magnetic moment of the muon

Recently, the Budapest-Marseille-Wuppertal collaboration achieved sub-percent precision in the evaluation of the lowest-order hadronic vacuum polarization contribution to the muon $g_μ-2$ (arXiv:hep-lat/2002.12347v3). At this level of precision, isospin-symmetric QCD is not sufficient. In this contribution we review how QED and strong-isospin-breaking effects have been included in our work. Isospin breaking is implemented by expanding the relevant correlation functions to second order in the electric charge $e$ and to first order in $m_u-m_d$. The correction terms are then computed using isospin-symmetric configurations. The choice of this approach allows us to better distribute the available computing resources among the various contributions.

hep-lat↗
arXiv2021

Leading hadronic contribution to the muon magnetic moment from lattice QCD

We compute the leading order hadronic vacuum polarization (LO-HVP) contribution to the anomalous magnetic moment of the muon, $(g_μ-2)$, using lattice QCD. Calculations are performed with four flavors of 4-stout-improved staggered quarks, at physical quark masses and at six values of the lattice spacing down to 0.064~fm. All strong isospin breaking and electromagnetic effects are accounted for to leading order. The infinite-volume limit is taken thanks to simulations performed in volumes of sizes up to 11~fm. Our result for the LO-HVP contribution to $(g_μ-2)$ has a total uncertainty of 0.8\%. Compared to the result of the dispersive approach for this contribution, ours significantly reduces the tension between the standard model prediction for $(g_μ-2)$ and its measurement.

hep-lat↗
arXiv2020

Ab-initio calculation of the proton and the neutron's scalar couplings for new physics searches

Many low-energy, particle-physics experiments seek to reveal new fundamental physics by searching for very rare scattering events on atomic nuclei. The interpretation of their results requires quantifying the non-linear effects of the strong interaction on the spin-independent couplings of this new physics to protons and neutrons. Here we present a fully-controlled, ab-initio calculation of these couplings to the quarks within those constituents of nuclei. We use lattice quantum chromodynamics computations for the four lightest species of quarks and heavy-quark expansions for the remaining two. We determine each of the six quark contributions with an accuracy better than 15%. Our results are especially important for guiding and interpreting experimental searches for our universe's dark matter.

hep-lat↗
arXiv2018

Hadronic vacuum polarization contribution to the anomalous magnetic moments of leptons from first principles

We compute the leading, strong-interaction contribution to the anomalous magnetic moment of the electron, muon and tau using lattice quantum chromodynamics (QCD) simulations. Calculations include the effects of $u$, $d$, $s$ and $c$ quarks and are performed directly at the physical values of the quark masses and in volumes of linear extent larger than $6\,\mathrm{fm}$. All connected and disconnected Wick contractions are calculated. Continuum limits are carried out using six lattice spacings. We obtain $a_e^\mathrm{LO-HVP}=189.3(2.6)(5.6)\times 10^{-14}$, $a_μ^\mathrm{LO-HVP}=711.1(7.5)(17.4)\times 10^{-10}$ and $a_τ^\mathrm{LO-HVP}=341.0(0.8)(3.2)\times 10^{-8}$, where the first error is statistical and the second is systematic.

hep-lat↗
arXiv2016

Slope and curvature of the hadron vacuum polarization at vanishing virtuality from lattice QCD

We compute the slope and curvature, at vanishing four-momentum transfer squared, of the leading order hadron vacuum polarization function, using lattice QCD. Calculations are performed with 2+1+1 flavors of staggered fermions directly at the physical values of the quark masses and in volumes of linear extent larger than 6fm. The continuum limit is carried out using six different lattice spacings. All connected and disconnected contributions are calculated, up to and including those of the charm.

hep-lat↗
arXiv2016

Lattice QCD for Cosmology

We present a full result for the equation of state (EoS) in 2+1+1 (up/down, strange and charm quarks are present) flavour lattice QCD. We extend this analysis and give the equation of state in 2+1+1+1 flavour QCD. In order to describe the evolution of the universe from temperatures several hundreds of GeV to several tens of MeV we also include the known effects of the electroweak theory and give the effective degree of freedoms. As another application of lattice QCD we calculate the topological susceptibility (chi) up to the few GeV temperature region. These two results, EoS and chi, can be used to predict the dark matter axion's mass in the post-inflation scenario and/or give the relationship between the axion's mass and the universal axionic angle, which acts as a initial condition of our universe.

hep-lat↗
arXiv2015

QCD thermodynamics with continuum extrapolated dynamical overlap fermions

We study the finite temperature transition in QCD with two flavors of dynamical fermions at a pseudoscalar pion mass of about 350 MeV. We use lattices with temporal extent of $N_t$=8, 10 and 12. For the first time in the literature a continuum limit is carried out for several observables with dynamical overlap fermions. These findings are compared with results obtained within the staggered fermion formalism at the same pion masses and extrapolated to the continuum limit. The presented results correspond to fixed topology and its effect is studied in the staggered case. Nice agreement is found between the overlap and staggered results.

hep-lat↗
arXiv2015

Ab initio calculation of the neutron-proton mass difference

The existence and stability of atoms rely on the fact that neutrons are more massive than protons. The measured mass difference is only 0.14\% of the average of the two masses. A slightly smaller or larger value would have led to a dramatically different universe. Here, we show that this difference results from the competition between electromagnetic and mass isospin breaking effects. We performed lattice quantum-chromodynamics and quantum-electrodynamics computations with four nondegenerate Wilson fermion flavors and computed the neutron-proton mass-splitting with an accuracy of $300$ kilo-electron volts, which is greater than $0$ by $5$ standard deviations. We also determine the splittings in the $Σ$, $Ξ$, $D$ and $Ξ_{cc}$ isospin multiplets, exceeding in some cases the precision of experimental measurements.

hep-lat↗
arXiv2014

Isospin splittings in the light baryon octet from lattice QCD and QED

While electromagnetic and up-down quark mass difference effects on octet baryon masses are very small, they have important consequences. The stability of the hydrogen atom against beta decay is a prominent example. Here we include these effects by adding them to valence quarks in a lattice QCD calculation based on $N_f=2+1$ simulations with 5 lattice spacings down to 0.054 fm, lattice sizes up to 6 fm and average up-down quark masses all the way down to their physical value. This allows us to gain control over all systematic errors, except for the one associated with neglecting electromagnetism in the sea. We compute the octet baryon isomultiplet mass splittings, as well as the individual contributions from electromagnetism and the up-down quark mass difference. Our results for the total splittings are in good agreement with experiment.

hep-lat↗
arXiv2012

QCD equation of state at nonzero chemical potential: continuum results with physical quark masses at order mu^2

We determine the equation of state of QCD for nonzero chemical potentials via a Taylor expansion of the pressure. The results are obtained for N_f=2+1 flavors of quarks with physical masses, on various lattice spacings. We present results for the pressure, interaction measure, energy density, entropy density, and the speed of sound for small chemical potentials. At low temperatures we compare our results with the Hadron Resonance Gas model. We also express our observables along trajectories of constant entropy over particle number. A simple parameterization is given (the Matlab/Octave script parameterization.m, submitted to the arXiv along with the paper), which can be used to reconstruct the observables as functions of T and mu, or as functions of T and S/N.

hep-lat↗
arXiv2012

Precision SU(3) lattice thermodynamics for a large temperature range

We present the equation of state (pressure, trace anomaly, energy density and entropy density) of the SU(3) gauge theory from lattice field theory in an unprecedented precision and temperature range. We control both finite size and cut-off effects. The studied temperature window (0.7...1000 T_c) stretches from the glueball dominated system into the perturbative regime, which allows us to discuss the range of validity of these approaches. We also determine the preferred renormalization scale of the Hard Thermal Loop scheme and we fit the unknown g^6 order perturbative coefficient at extreme high temperatures T>100 T_c. We furthermore quantify the nonperturbative contribution to the trace anomaly using a simple functional form. Our high precision data allows one to have a complete theoretical description of the equation of state from T=0 all the way to the phase transition, through the transition region into the perturbative regime up to the Stefan-Boltzmann limit. We will discuss this description, too.

hep-lat↗
arXiv2011

Lattice SU(3) thermodynamics and the onset of perturbative behaviour

We present the equation of state (pressure, trace anomaly, energy density and entropy density) of the SU(3) gauge theory from lattice field theory in an unprecedented precision and temperature range. We control both finite size and cut-off effects. The studied temperature window ($0.7... 1000 T_c$) stretches from the glueball dominated system into the perturbative regime, which allows us to discuss the range of validity of these approaches. From the critical couplings on fine lattices we get $T_c/\Lambdamsbar=1.26(7)$ and use this ratio to express the perturbative free energy in $T_c$ units. We also determine the preferred renormalization scale of the Hard Thermal Loop scheme and we fit the unknown $g^6$ order perturbative coefficient at extreme high temperatures $T>100T_c$. We furthermore quantify the nonperturbative contribution to the trace anomaly using two simple functional forms.

hep-ph↗
arXiv2009

The QCD transition temperature: results with physical masses in the continuum limit II.

We extend our previous study [Phys. Lett. B643 (2006) 46] of the cross-over temperatures (T_c) of QCD. We improve our zero temperature analysis by using physical quark masses and finer lattices. In addition to the kaon decay constant used for scale setting we determine four quantities (masses of the Ωbaryon, K^*(892) and ϕ(1020) mesons and the pion decay constant) which are found to agree with experiment. This implies that --independently of which of these quantities is used to set the overall scale-- the same results are obtained within a few percent. At finite temperature we use finer lattices down to a <= 0.1 fm (N_t=12 and N_t=16 at one point). Our new results confirm completely our previous findings. We compare the results with those of the 'hotQCD' collaboration.

hep-lat↗
arXiv2008

Low-cost fermions in classical field simulations

We discuss the possible extension of the bosonic classical field theory simulations to include fermions. This problem has been addressed in terms of the inhomogeneous mean field approximation by Aarts and Smit. By performing a stochastic integration of an equivalent set of equations we can extend the original 1+1 dimensional calculations so that they become feasible in higher dimensions. We test the scheme in 2 + 1 dimensions and discuss some classical applications with fermions for the first time, such as the decay of oscillons.

hep-ph↗
arXiv2006

Lattice simulations of real-time quantum fields

We investigate lattice simulations of scalar and nonabelian gauge fields in Minkowski space-time. For SU(2) gauge-theory expectation values of link variables in 3+1 dimensions are constructed by a stochastic process in an additional (5th) ``Langevin-time''. A sufficiently small Langevin step size and the use of a tilted real-time contour leads to converging results in general. All fixed point solutions are shown to fulfil the infinite hierarchy of Dyson-Schwinger identities, however, they are not unique without further constraints. For the nonabelian gauge theory the thermal equilibrium fixed point is only approached at intermediate Langevin-times. It becomes more stable if the complex time path is deformed towards Euclidean space-time. We analyze this behavior further using the real-time evolution of a quantum anharmonic oscillator, which is alternatively solved by diagonalizing its Hamiltonian. Without further optimization stochastic quantization can give accurate descriptions if the real-time extend of the lattice is small on the scale of the inverse temperature.

hep-lat↗