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L. Cosmai

Publications and source records attributed to L. Cosmai.

At least 55 records · Page 3Linked to original sources
arXiv2000

A gauge invariant study of the monopole condensation in non Abelian lattice gauge theories

We investigate the Abelian monopole condensation in finite temperature SU(2) and SU(3) pure lattice gauge theories. To this end we introduce a gauge invariant disorder parameter built up in terms of the lattice Schrödinger functional. Our numerical results show that the disorder parameter is different from zero and Abelian monopole condense in the confined phase. On the other hand our numerical data suggest that the disorder parameter tends to zero, in the thermodynamic limit, when the gauge coupling constant approaches the critical deconfinement value. In the case of SU(3) we also compare the different kinds of Abelian monopoles which can be defined according to the choice of the Abelian subgroups.

hep-lat↗
arXiv2000

Topology in 2D CP**(N-1) models on the lattice: a critical comparison of different cooling techniques

Two-dimensional CP**(N-1) models are used to compare the behavior of different cooling techniques on the lattice. Cooling is one of the most frequently used tools to study on the lattice the topological properties of the vacuum of a field theory. We show that different cooling methods behave in an equivalent way. To see this we apply the cooling methods on classical instantonic configurations and on configurations of the thermal equilibrium ensemble. We also calculate the topological susceptibility by using the cooling technique.

hep-lat↗
arXiv1999

Abelian monopole condensation in lattice gauge theories

We investigate the dynamics of lattice gauge theories in an Abelian monopole background field. By means of the gauge-invariant lattice Schrodinger functional we study the Abelian monopole condensation in U(1) lattice gauge theory at zero temperature and in SU(3) lattice gauge theory at finite temperature.

hep-lat↗
arXiv1999

Large rescaling of the Higgs condensate: theoretical motivations and lattice results

In the Standard Model the Fermi constant is associated with the vacuum expectation value of the Higgs field, `the condensate', usually believed to be a cutoff-independent quantity. General arguments related to the `triviality' of $Φ^4$ theory in 4 space-time dimensions suggest, however, a dramatic renormalization effect in the continuum limit that is clearly visible on the relatively large lattices available today. The result can be crucial for the Higgs phenomenology and in any context where spontaneous symmetry breaking is induced through scalar fields.

hep-lat↗
arXiv1999

Further lattice evidence for a large re-scaling of the Higgs condensate

Using a high-statistics lattice simulation of the Ising limit of $(λΦ^4)_4$ theory, we have measured the susceptibility and propagator in the broken phase. We confirm our earlier finding of a discrepancy between the field re-scaling implied by the propagator data and that implied by the susceptibility. The discrepancy becomes {\it worse} as one goes closer to the continuum limit; thus, it cannot be explained by residual perturbative effects. The data are consistent with an unconventional description of symmetry breaking and ``triviality'' in which the re-scaling factor for the finite-momentum fluctuations tends to unity, but the re-scaling factor for the condensate becomes larger and larger as one approaches the continuum limit. In the Standard Model this changes the interpretation of the Fermi-constant scale and its relation to the Higgs mass.

hep-lat↗
arXiv1998

First lattice evidence for a non-trivial renormalization of the Higgs condensate

General arguments related to ``triviality'' predict that, in the broken phase of $(λΦ^4)_4$ theory, the condensate $<Φ>$ re-scales by a factor $Z_ϕ$ different from the conventional wavefunction-renormalization factor, $Z_{prop}$. Using a lattice simulation in the Ising limit we measure $Z_ϕ=m^2 χ$ from the physical mass and susceptibility and $Z_{prop}$ from the residue of the shifted-field propagator. We find that the two $Z$'s differ, with the difference increasing rapidly as the continuum limit is approached. Since $Z_ϕ$ affects the relation of $<Φ>$ to the Fermi constant it can sizeably affect the present bounds on the Higgs mass.

hep-lat↗
arXiv1997

The $(λΦ^4)_4$ theory on the lattice: effective potential and triviality

We compute numerically the effective potential for the $(λΦ^4)_4$ theory on the lattice. Three different methods were used to determine the critical bare mass for the chosen bare coupling value. Two different methods for obtaining the effective potential were used as a control on the results. We compare our numerical results with three theoretical descriptions. Our lattice data are in quite good agreement with the ``Triviality and Spontaneous Symmetry Breaking'' picture.

hep-lat↗
arXiv1997

A lattice test of alternative interpretations of ``triviality'' in $(λΦ^4)_4$ theory

There are two physically different interpretations of ``triviality'' in $(λΦ^4)_4$ theories. The conventional description predicts a second-order phase transition and that the Higgs mass $m_h$ must vanish in the continuum limit if $v$, the physical v.e.v, is held fixed. An alternative interpretation, based on the effective potential obtained in ``triviality-compatible'' approximations (in which the shifted `Higgs' field $h(x)\equiv Φ(x)-<Φ>$ is governed by an effective quadratic Hamiltonian) predicts a phase transition that is very weakly first-order and that $m_h$ and $v$ are both finite, cutoff-independent quantities. To test these two alternatives, we have numerically computed the effective potential on the lattice. Three different methods were used to determine the critical bare mass for the chosen bare coupling value. All give excellent agreement with the literature value. Two different methods for obtaining the effective potential were used, as a control on the results. Our lattice data are fitted very well by the predictions of the unconventional picture, but poorly by the conventional picture.

hep-ph↗
arXiv1996

Lattice effective potential of $(λΦ^4)_4$: nature of the phase transition and bounds on the Higgs mass

We present a detailed discussion of Spontaneous Symmetry Breaking (SSB) in $(λΦ^4)_4$. In the usual approach, inspired by perturbation theory, one predicts a second-order phase transition, the Higgs mass $m_h$, related to the value of the renormalized 4-point coupling, gets smaller when increasing the ultraviolet cutoff and this leads to the generally quoted upper bounds $m_h<$700-900 GeV. On the other hand, by exploring the structure of the effective potential in those approximation consistent with `triviality', where the Higgs mass does not represent a measure of any observable interaction, SSB does not require an ultraviolet cutoff, the phase transition is first-order, such that the massless `Coleman-Weinberg' regime lies in the broken phase, and one gets only $m_h<$3 TeV from vacuum stability. To separate out the two alternatives, we present a precise lattice computation of the slope of the effective potential in the region of bare parameters indicated by the Luscher~\&~Weisz and Brahm's analysis of the critical line. Our lattice data strongly support the latter description of SSB. Indeed, our data cannot be reproduced in perturbation theory, and then they confirm the existence on the lattice of a remarkable phase of $(λΦ^4)_4$ where SSB is generated through ``dimensional transmutation'', and show no evidence for residual self-interaction effects of the shifted ``Higgs'' field $h(x)=Φ(x)-\langleΦ\rangle$, in agreement with ``triviality''.

hep-th↗
arXiv1996

The Lattice Schrodinger Functional and the Background Field Effective Action

We propose a new method that by using the lattice Schrödinger functional allows to investigate the effective action for external background fields in lattice gauge theories. We show that this method gives sensible results for the case of four-dimensional U(1) gauge theory in an external constant magnetic field.

hep-lat↗
arXiv1995

Lattice effective potential of massless $(λΦ^4)_4$: `triviality' and spontaneous symmetry breaking

We present a precise lattice computation of the slope of the effective potential for massless $(λΦ^4)_4$ theory in the region of bare parameters indicated by the Brahm's analysis of lattice data. Our results confirm the existence on the lattice of a remarkable phase of $(λΦ^4)_4$ where Spontaneous Symmetry Breaking is generated through ``dimensional transmutation''. The resulting effective potential shows no evidence for residual self-interaction effects of the shifted `Higgs' field $h(x)=Φ(x)-\langleΦ\rangle$, as predicted by ``triviality'', and cannot be reproduced in perturbation theory. Accordingly the mass of the Higgs particle, by itself, does not represent a measure of any observable interaction.

hep-th↗
arXiv1994

Dual Meissner Effect and String Tension in SU(2) Lattice Gauge Theory

We study the distribution of the color fields due to a static quark-antiquark pair in SU(2) lattice gauge theory. We find that the London penetration length measured after Abelian projection in the Abelian Covariant gauge (Maximal Abelian gauge) agrees with the one obtained without gauge fixing. Moreover the penetration length scales according to asymptotic freedom. We put out a simple relation between the penetration length and the string tension.

hep-lat↗
arXiv1993

On the Meissner effect in SU(2) lattice gauge theory

We investigate the dual superconductor model of color confinement in SU(2) lattice gauge theory. We find that the transverse distribution of the longitudinal chromoelectric field between static quarks displays the dual Meissner effect. We also give evidence that the problem of color confinement could be approached in the framework of the 't~Hooft's Abelian projection.

hep-lat↗
arXiv1993

Unstable Modes in Three-Dimensional SU(2) Gauge Theory

We investigate SU(2) gauge theory in a constant chromomagnetic field in three dimensions both in the continuum and on the lattice. Using a variational method to stabilize the unstable modes, we evaluate the vacuum energy density in the one-loop approximation. We compare our theoretical results with the outcomes of the numerical simulations.

hep-lat↗