arXiv subjects

Claudio Bonati

Publications and source records attributed to Claudio Bonati.

122 records · Page 7Linked to original sources

arXiv2013

Change of theta dependence in 4D SU(N) gauge theories across the deconfinement transition

We investigate the dependence of four-dimensional SU(N) gauge theories on the topological theta term at finite temperature and, in particular, across the deconfinement transition. For this purpose, we exploit the lattice formulation of the theory and present numerical results for the expansion of the free energy up to O(theta^6), for N=3 and N=6. Our numerical analysis shows that the theta dependence of 4D SU(N) gauge theory experiences a drastic change across the deconfinement transition: the low-temperature phase is characterized by a large-N scaling with theta/N as relevant variable, while in the high-temperature phase the scaling variable is just theta and the free energy is essentially determined by the instanton-gas approximation. The crossover between the two different behaviours gets sharper with increasing N, suggesting that the instanton-gas regime sets in just above Tc at large N.

hep-lat↗

arXiv2012

Variations on the magnetic torque acting on a wire

The relation M = mu x B is presented in all elementary courses on electromagnetism but it is usually given just for the simple case of a rectangular wire. We will present a completely general but elementary proof of this relation together with two more advanced proof methods. We will then provide some extensions: non-closed wires and non-uniform magnetic field.

physics.class-ph↗

arXiv2012

The disorder parameter of dual superconductivity in QCD revisited

We discover the origin of the pathologies of the disorder parameter used in previous papers to detect dual superconductivity of QCD vacuum, and we remove them by defining an improved disorder parameter. A check of the approach is made by numerical simulations of SU(2) gauge theory, which demonstrate that the approach is consistent and with it that deconfinement is a transition from dual superconductor to normal.

hep-lat↗

arXiv2012

Constraints on the two-flavor QCD phase diagram from imaginary chemical potential

We review our knowledge of the phase diagram of QCD as a function of temperature, chemical potential and quark masses. The presence of tricritical lines at imaginary chemical potential mu=i pi/3 T, with known scaling behaviour in their vicinity, puts constraints on this phase diagram, especially in the case of two light flavors. We show first results in our project to determine the finite-temperature behaviour in the two-flavour chiral limit.

hep-lat↗

arXiv2011

QCD simulations with staggered fermions on GPUs

We report on our implementation of the RHMC algorithm for the simulation of lattice QCD with two staggered flavors on Graphics Processing Units, using the NVIDIA CUDA programming language. The main feature of our code is that the GPU is not used just as an accelerator, but instead the whole Molecular Dynamics trajectory is performed on it. After pointing out the main bottlenecks and how to circumvent them, we discuss the obtained performances. We present some preliminary results regarding OpenCL and multiGPU extensions of our code and discuss future perspectives.

hep-lat↗

arXiv2011

Finite temperature effective string corrections in (3+1)D SU(2) lattice gauge theory

We study the effective string corrections to the inter-quark potential at finite temperature by simulating the SU(2) lattice gauge theory in four dimensions. We provide the first numerical evidence that the logarithmic correction to the potential, which was recently proposed to be a signature of the effective string at finite temperature, is universal also in (3+1)D gauge theory, thus extending previous results limited to the (2+1)D case.

hep-lat↗

arXiv2011

The Roberge-Weiss endpoint in N_f = 2 QCD

We present the results of extensive simulations regarding the critical behavior at the endpoint of the Roberge-Weiss transition for N_f = 2 QCD. We confirm early evidence, presented in arXiv:0909.0254, according to which the Roberge-Weiss endpoint is first order in the limit of large or small quark masses, and second order for intermediate masses. A systematic study of the transition strength as a function of the quark mass in the first order regions, permits us to estimate the tricritical values of the quark mass separating the second order region from the first order ones.

hep-lat↗

arXiv2011

Armchair graphene nanoribbons: PT-symmetry breaking and exceptional points without dissipation

We consider a single layer graphene nanoribbon with armchair edges in a longitudinally constant external potential and point out that its transport properties can be described by means of an effective non-Hermitian Hamiltonian. We show that this system has some features typical of dissipative systems, namely the presence of exceptional points and of PT-symmetry breaking, although it is not dissipative.

cond-mat.mes-hall↗

arXiv2011

Toward a well defined monopole creation operator

The lattice implementation of monopole creation operator proves to have problems related to bulk transitions that can possibly affect the interpretation of its mean value as an order parameter for monopole condensation. Preliminary evidence is presented that these unexpected behaviours are in fact only due to lattice artefacts and do not spoil the physical interpretation of the monopole operator.

hep-lat↗

arXiv2010

The three-dimensional, three state Potts model in a negative external field

We investigate the critical behaviour of the three-dimensional, three state Potts model in presence of a negative external field h, i.e. disfavouring one of the three states. A genuine phase transition is present for all values of |h|, corresponding to the spontaneous breaking of a residual Z_2 symmetry. The transition is first/second order respectively for small/large values of |h|, with a tricritical field h_tric separating the two regimes. We provide, using different and consistent approaches, a precise determination of h_tric; we also compare with previous studies and discuss the relevance of our investigation to analogous studies of the QCD phase diagram in presence of an imaginary chemical potential.

hep-lat↗

arXiv2010

Detecting monopoles on the lattice

We address the issue why the number and the location of magnetic monopoles detected on lattice configurations are gauge dependent, in contrast with the physical expectation that monopoles have a gauge invariant status. By use of the Non-Abelian Bianchi Identities we show that monopoles are gauge invariant, but the efficiency of the technique usually adopted to detect them depends on the choice of the gauge in a well understood way. In particular we have studied a class of gauges which interpolates between the Maximal Abelian gauge, where all monopoles are observed, and the Landau gauge, where all monopoles escape detection.

hep-lat↗

arXiv2010

Non abelian Bianchi identities, monopoles and gauge invariance

A direct connection is proved between the Non-Abelian Bianchi Identities and the Abelian Bianchi identities for the 't Hooft tensor in a generic gauge; the existence of a magnetic current is related to the violation of NABI's. Using this relation it is shown that not all gauges are equivalent to detect monopoles on the lattice, that e.g. the Maximal Abelian Gauge is a legitimate choice while the Landau gauge is not. Nevertheless monopole condensation is found to be a gauge invariant property.

hep-lat↗

arXiv2010

Staggered fermions simulations on GPUs

We present our implementation of the RHMC algorithm for staggered fermions on Graphics Processing Units using the NVIDIA CUDA programming language. While previous studies exclusively deal with the Dirac matrix inversion problem, our code performs the complete MD trajectory on the GPU. After pointing out the main bottlenecks and how to circumvent them, we discuss the performance of our code.

hep-lat↗

arXiv2010

Monopoles, abelian projection, and gauge invariance

A direct connection is proved between the Non-Abelian Bianchi Identities(NABI), and the abelian Bianchi identities for the 't Hooft tensor. As a consequence the existence of a non-zero magnetic current is related to the violation of the NABI's and is a gauge-invariant property. The construction allows to show that not all abelian projections can be used to expose monopoles in lattice configurations: each field configuration with non-zero magnetic charge identifies its natural projection, up to gauge transformations which tend to unity at large distances. It is shown that the so-called maximal-abelian gauge is a legitimate choice. It is also proved, starting from the NABI, that monopole condensation is a physical gauge invariant phenomenon, independent of the choice of the abelian projection.

hep-lat↗