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Matteo Beccaria

Publications and source records attributed to Matteo Beccaria.

At least 127 records · Page 7Linked to original sources
arXiv2005

Electroweak supersymmetric effects on high energy unpolarized and polarized single top production at LHC

We consider various processes of single top production at LHC in the theoretical framework of the MSSM and examine the role of the supersymmetric electroweak one-loop corrections in a special moderately light SUSY scenario, in an initial parton-pair c.m. high energy range where a logarithmic asymptotic expansion of Sudakov type can be used. We show that the electroweak virtual effects are systematically large, definitely beyond the relative ten percent size, particularly for a final $tH^-$ pair where a special enhancement is present. We show then in a qualitative way the kind of precision tests of the model that would be obtainable from accurate measurements of the energy distributions of the various cross sections and of the top polarization asymmetries.

hep-ph↗
arXiv2005

Density Matrix Renormalization Group Study of the Disorder Line in the Quantum ANNNI Model

We apply Density Matrix Renormalization Group methods to study the phase diagram of the quantum ANNNI model in the region of low frustration where the ferromagnetic coupling is larger than the next-nearest-neighbor antiferromagnetic one. By Finite Size Scaling on lattices with up to 80 sites we locate precisely the transition line from the ferromagnetic phase to a paramagnetic phase without spatial modulation. We then measure and analyze the spin-spin correlation function in order to determine the disorder transition line where a modulation appears. We give strong numerical support to the conjecture that the Peschel-Emery one-dimensional line actually coincides with the disorder line. We also show that the critical exponent governing the vanishing of the modulation parameter at the disorder transition is $β_q = 1/2$.

cond-mat.stat-mech↗
arXiv2005

Critical behavior in a non-local interface model

The Raise and Peel model is a recently proposed one-dimensional statistical model describing a fluctuating interface. The evolution of the model follows from the competition between adsorption and desorption processes. The model is non-local due to the possible occurrence of avalanches. At a special ratio of the adsorption-desorption rates the model is integrable and many rigorous results are known. Off the critical point, the phase diagram and scaling properties are not known. In this paper, we search for indications of phase transition studying the gap in the spectrum of the non-hermitian generator of the stochastic interface evolution. We present results for the gap obtained from exact diagonalization and from Monte Carlo estimates derived from temporal correlations of various observables.

cond-mat.stat-mech↗
arXiv2005

Dynamical supersymmetry breaking and phase diagram of the lattice Wess-Zumino model

We study dynamical supersymmetry breaking and the transition point by non-perturbative lattice techniques in a class of two-dimensional N=1 Wess-Zumino model. The method is based on the calculation of rigorous lower bounds on the ground state energy density in the infinite-lattice limit. Such bounds are useful in the discussion of supersymmetry phase transition. The transition point is determined with this method and then compared with recent results based on large-scale Green Function Monte Carlo simulations with good agreement.

hep-lat↗
arXiv2005

D0-brane tension in string field theory

We compute the D0-brane tension in string field theory by representing it as a tachyon lump of the D1-brane compactified on a circle of radius $R$. To this aim, we calculate the lump solution in level truncation up to level L=8. The normalized D0-brane tension is independent on $R$. The compactification radius is therefore chosen in order to cancel the subleading correction $1/L^2$. We show that an optimal radius $R^*$ indeed exists and that at $R^*$ the theoretical prediction for the tension is reproduced at the level of $10^{-5}$. As a byproduct of our calculation we also discuss the determination of the marginal tachyon field at $R\to 1$.

hep-th↗
arXiv2005

Yukawa enhanced electroweak corrections at high energy in the MSSM

We consider the electroweak radiative corrections in the MSSM and study the purely Yukawa contributions ${\cal O}(α^L y_t^{2p} y_b^{2q})$, $p+q=L$, where $y_{t,b}$ are the top and bottom quark Yukawa couplings. We show that these corrections can be computed in a gaugeless limit of the MSSM where they are under Renormalization Group control. As an application, we present explicit results for various ILC and LHC processes valid at all orders in the loop expansion and at leading order in the large logarithms that arise at high energy.

hep-ph↗
arXiv2005

Sudakov Expansions and Top Quark Physics at LHC

We review some peculiar features of Sudakov expansions in the calculation of electroweak radiative corrections in the MSSM at high energy. We give specific examples and consider in particular the process b g -> t W of single top quark production relevant for the top quark physics programme at LHC.

hep-ph↗
arXiv2005

Supersymmetric structure of electroweak Sudakov corrections

Electroweak radiative corrections can be evaluated in the Sudakov approximation, a systematic high energy expansion known to be relevant for the analysis of future collider experiments in the TeV energy range. In the Minimal Supersymmetric Standard Model and at next-to-leading order, Sudakov electroweak corrections satisfy remarkable relations at the one loop level. Explicit computations in component fields are available for various different $2\to 2$ processes relevant for Linear Collider or LHC physics. The Sudakov corrections turn out to be equal or closely related in several classes of processes differing by the replacement of certain final or initial states with their superpartners. This fact suggests that supersymmetry is partially restored at high-energy. We analyze the supersymmetric structure of such relations by computing the Sudakov corrections in the framework of superfield perturbation theory. As a simple application, we derive in full details an extended complete set of supersymmetric relations among different processes related by supersymmetry to the fundamental fermion pair production process $e^+e^-\to f\bar f$.

hep-ph↗
arXiv2004

Exact Ground State and Finite Size Scaling in a Supersymmetric Lattice Model

We study a model of strongly correlated fermions in one dimension with extended N=2 supersymmetry. The model is related to the spin $S=1/2$ XXZ Heisenberg chain at anisotropy $Δ=-1/2$ with a real magnetic field on the boundary. We exploit the combinatorial properties of the ground state to determine its exact wave function on finite lattices with up to 30 sites. We compute several correlation functions of the fermionic and spin fields. We discuss the continuum limit by constructing lattice observables with well defined finite size scaling behavior. For the fermionic model with periodic boundary conditions we give the emptiness formation probability in closed form.

cond-mat.str-el↗
arXiv2004

Phase diagram of the lattice Wess-Zumino model from rigorous lower bounds on the energy

We study the lattice N=1 Wess-Zumino model in two dimensions and we construct a sequence $ρ^{(L)}$ of exact lower bounds on its ground state energy density $ρ$, converging to $ρ$ in the limit $L\to\infty$. The bounds $ρ^{(L)}$ can be computed numerically on a finite lattice with $L$ sites and can be exploited to discuss dynamical symmetry breaking. The transition point is determined and compared with recent results based on large-scale Green Function Monte Carlo simulations with good agreement.

hep-lat↗
arXiv2004

Supersymmetry breaking in two dimensions: the lattice N=1 Wess-Zumino model

We study dynamical supersymmetry breaking by non perturbative lattice techniques in a class of two-dimensional N=1 Wess-Zumino models. We work in the Hamiltonian formalism and analyze the phase diagram by analytical strong-coupling expansions and explicit numerical simulations with Green Function Monte Carlo methods.

hep-lat↗
arXiv2003

Level truncation and the quartic tachyon coupling

We discuss the convergence of level truncation in bosonic open string field theory. As a test case we consider the calculation of the quartic tachyon coupling $γ_4$. We determine the exact contribution from states up to level L=28 and discuss the $L\to\infty$ extrapolation by means of the BST algorithm. We determine in a self-consistent way both the coupling and the exponent $ω$ of the leading correction to $γ_4$ at finite $L$ that we assume to be $\sim 1/L^ω$. The results are $γ_4 = -1.7422006(9)$ and $|ω-1|\lesssim 10^{-4}$.}

hep-th↗
arXiv2003

Reliability of a high energy one-loop expansion of e+e- --> W+W- in the SM and in the MSSM

We compare the logarithmic Sudakov expansions of the process e+e- --> W+W- in the one-loop approximation and in the resummed version, to subleading order accuracy, in the SM case and in a light SUSY scenario for the MSSM. We show that the two expansions are essentially identical below 1 TeV, but differ drastically at higher (2,3 TeV) center of mass energies. Starting from these conclusions, we argue that a complete one-loop calculation in the energy region below 1 TeV does not seem to need extra two-loop corrections, in spite of the relatively large size of the one-loop effects.

hep-ph↗
arXiv2003

Sudakov expansions at one loop and beyond for charged scalar and fermion pair production in SUSY models at future Linear Colliders

We consider the high energy behaviour of the amplitudes for pair production of charged leptons, quarks, Higgs bosons, sleptons, squarks and charginos at lepton colliders. We give the general expressions of the leading quadratic and subleading linear logarithms that appear at the one loop level, and derive the corresponding resummed expansions to \underline{subleading} logarithmic order accuracy. Under the assumption of a relatively light SUSY scenario and choosing the MSSM as a specific model, we compare the predictions of the one-loop and of the resummed expansions at variable energy. We show that the two predictions are very close in the one TeV regime, but drastically differ in the few ($2,3$) TeV range.

hep-ph↗
arXiv2003

World-Line Path Integral Study of Supersymmetry Breaking in the Wess-Zumino Model

We study supersymmetry breaking in the lattice N=1 Wess-Zumino model by the world-line path integral algorithm. The ground state energy and supersymmetric Ward identities are exploited to support the expected symmetry breaking in finite volume. Non-Gaussian fluctuations of the topological charge are discussed and related to the infinite volume transition.

hep-lat↗
arXiv2002

A Hamiltonian lattice study of the two-dimensional Wess-Zumino model

We investigate a Hamiltonian lattice version of the two-dimensional Wess-Zumino model by Quantum Monte Carlo simulations. In order to study the pattern of supersymmetry breaking, we measure the ground state energy and the correlation length along a trajectory approaching the continuum limit. The algorithm is very effective in measuring the ground state energy, and adequate for the correlation length.

hep-lat↗
arXiv2002

Cluster Percolation and Chiral Phase Transition

The Meron Cluster algorithm solves the sign problem in a class of interacting fermion lattice models with a chiral phase transition. Within this framework, we study the geometrical features of the clusters built by the algorithm, that suggest the occurrence of a generalized percolating phase transition at the chiral critical temperature in close analogy with Fortuin-Kasteleyn percolation in spin models.

hep-lat↗