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L. Cosmai

Publications and source records attributed to L. Cosmai.

At least 37 records · Page 2Linked to original sources
arXiv2011

The trivial Higgs boson: first evidences from LHC

We further elaborate on the triviality and spontaneous symmetry breaking scenario where the Higgs boson without self-interaction coexists with spontaneous symmetry breaking. The trivial Higgs boson is rather heavy with mass m_H = 754 +/- 20 (stat) +/- 20 (syst) GeV and total width Γ(H) \simeq 320 GeV. We briefly discuss the experimantal signatures of our trivial Higgs and compare with the recent results from ATLAS collaboration. We argue that experimental data seem to support our scenario.

hep-ph↗
arXiv2010

The critical line of QCD with four degenerate quarks

We determine the pseudo-critical couplings at imaginary chemical potentials by high-statistics Monte Carlo simulations of QCD with four degenerate quarks at non-zero temperature and baryon density by the method of analytic continuationan. We reveal deviations from the simple quadratic dependence on the chemical potential visible in earlier works on the same subject. Finally, we discuss the implications of our findings for the shape of the pseudo-critical line at real chemical potential, comparing different possible extrapolations.

hep-lat↗
arXiv2010

Analytic continuation in QCD-like theories at finite density and finite isospin

The method of analytic continuation is one of the most powerful tools to circumvent the sign problem in lattice QCD. The present study is part of a larger project which, based on the investigation of QCD-like theories which are free of the sign problem, is aimed at testing the validity of the method of analytic continuation and at improving its predictivity, in view of its application to real QCD. We have shown that a considerable improvement can be achieved if suitable functions are used to interpolate data with imaginary chemical potential. We present results obtained in a theory free of the sign problem such as two-color QCD at finite chemical potential.

hep-lat↗
arXiv2006

Analytical continuation from imaginary to real chemical potential in 2-color QCD under scrutiny

The method of analytical continuation from imaginary to real chemical potential is tested in 2-color QCD. In comparison to previous studies in the same theory, an exact updating algorithm is used and simulations are performed closer to the thermodynamic limit. It is shown that the method considerably improves if suitable functions are used to interpolate data with imaginary chemical potential.

hep-lat↗
arXiv2005

Large logarithmic rescaling of the scalar condensate: a subtlety with substantial phenomenological implications

Lattice data, taken since 1998 near the critical line of a 4D Ising model, have been supporting the large logarithmic rescaling of the scalar condensate predicted in the alternative description of symmetry breaking proposed by Consoli and Stevenson. This conclusion has been challenged in a recent paper by Balog et al. In this paper we respond to the criticism of these authors, recapitulate the theoretical and numerical evidences in favour of the alternative interpretation of `triviality' and reiterate our conclusion: `triviality', by itself, cannot be used to place upper bounds on the Higgs boson mass.

hep-lat↗
arXiv2004

External Fields and Color Confinement

U(1), SU(2), and SU(3) lattice gauge theories in presence of external fields are investigated both in (3+1) and (2+1) dimensions. The free energy of gauge systems has been measured. While the phase transition in compact U(1) is not influenced by the strength of an external constant magnetic field, the deconfinement temperature for SU(2) and SU(3) gauge systems in a constant abelian chromomagnetic field decreases when the strength of the applied field increases. The dependence of the deconfinement temperature on the strength of an external constant chromomagnetic field seems to be a peculiar feature of non abelian gauge theories.

hep-lat↗
arXiv2004

Large logarithmic rescaling of the scalar condensate: new lattice evidences

Using two different methods, we have determined the rescaling of the scalar condensate $Z\equiv Z_ϕ$ near the critical line of a 4D Ising model. Our lattice data, in agreement with previous numerical indications, support the behavior $Z_ϕ\sim \ln (Λ)$, $Λ$ being the ultraviolet cutoff. This result is predicted in an alternative description of symmetry breaking where there are no upper bounds on the Higgs boson mass from `triviality'.

hep-lat↗
arXiv2003

Lattice measurement of the rescaling of the scalar condensate

We have determined the rescaling of the scalar condensate $Z\equiv Z_ϕ$ near the critical line of a 4D Ising model. Our lattice data, supporting previous numerical indications, confirm the behaviour $Z_ϕ\sim \ln ({\rm cutoff})$. This result is predicted in an alternative description of symmetry breaking where there are no upper bounds on the Higgs boson mass from `triviality'.

hep-ph↗
arXiv2003

Indications on the Higgs boson mass from lattice simulations

The `triviality' of $Φ^4_4$ has been traditionally interpreted within perturbation theory where the prediction for the Higgs boson mass depends on the magnitude of the ultraviolet cutoff $Λ$. This approach crucially assumes that the vacuum field and its quantum fluctuations rescale in the same way. The results of the present lattice simulation, confirming previous numerical indications, show that this assumption is not true. As a consequence, large values of the Higgs mass $m_H$ can coexist with the limit $Λ\to \infty $. As an example, by extrapolating to the Standard Model our results obtained in the Ising limit of the one-component theory, one can obtain a value as large as $m_H=760 \pm 21$ GeV, independently of $Λ$.

hep-lat↗
arXiv2003

Investigations on the deconfining phase transition in QCD

We investigate the deconfining phase transition in SU(3) pure gauge theory and in full QCD with two flavors of staggered fermions by means of a gauge invariant thermal partition functional. In the pure gauge case our finite size scaling analysis is in agreement with the well known weak first order phase transition. In the case of 2 flavors full QCD we find that the phase transition is consistent with weak first order, contrary to the expectation of a crossover for not too large quark masses.

hep-lat↗
arXiv2003

New indications on the Higgs boson mass from lattice simulations

The `triviality' of $Φ^4_4$ has been traditionally interpreted within perturbation theory where the prediction for the Higgs boson mass depends on the magnitude of the ultraviolet cutoff $Λ$. This approach crucially assumes that the vacuum field and its quantum fluctuations rescale in the same way. The results of the present lattice simulation, confirming previous numerical indications, show that this assumption is not true. As a consequence, large values of the Higgs mass $m_H$ can coexist with the limit $Λ\to \infty $. As an example, by extrapolating to the Standard Model our results obtained in the Ising limit of the one-component theory, one can obtain a value as large as $m_H=760 \pm 21$ GeV, independently of $Λ$.

hep-ph↗
arXiv2001

Dynamics of the Scalar Condensate in thermal 4D self-interacting Scalar Field Theory on the Lattice

We simulate a four dimensional self-interacting scalar field theory on the lattice at finite temperature. By varying temperature, the system undergoes a phase transition from broken phase to symmetric phase. Our data show that the zero-momentum field renormalization increases by approaching critical temperature. On the other hand, finite-momentum wave-function renormalization remains remarkably constant.

hep-lat↗
arXiv2001

Lattice measurement of the energy-gap in a spontaneously broken phase

Using lattice simulations of a one-component $(λΦ^4)_4$ theory, we have measured the energy spectrum $ω({\mathbf{k}})$ in the broken phase at various lattice sizes. Our data show that the energy-gap $ω(0)$ is {\it not} the `Higgs mass' $M_h$ but an infrared-sensitive quantity that becomes smaller and smaller by increasing the lattice size and may even vanish in the infinite-volume limit.

hep-ph↗
arXiv2001

Abelian chromomagnetic background field at finite temperature on the lattice

The vacuum dynamics of SU(2) and SU(3) lattice gauge theories is studied by means of a gauge-invariant effective action defined using the lattice Schrödinger functional at finite temperature. In the case of the SU(3) gauge theory numerical simulations are performed both at zero and finite temperature. The vacuum is probed using an external constant Abelian chromomagnetic field. At zero temperature, in agreement with our previous studies for the SU(2) theory, the external field is totally screened in the continuum limit. At finite temperature numerical data suggest that confinement is restored by increasing the strength of the applied field.

hep-lat↗
arXiv2001

Lattice measurement of the scalar propagator near the symmetry breaking phase transition

Recent lattice simulations of $(λΦ^4)_4$ theories in the broken phase show that : a) the shifted field propagator is well reproduced by the simple 2-parameter form ${Z_{\rm prop}\over{p^2 + M^2_h}}$ at finite momenta but strongly differs for $p \to 0$ b) the bare zero-momentum two-point function $Γ_2(0)= \frac{d^2 V_{\rm eff}}{d ϕ^2_B}|_{ϕ_B= \pm v_B}$ gives a value of $Z_ϕ\equiv {{M^2_h}\over{Γ_2(0)}}$ that increases when approaching the continuum limit. This supports theoretical expectations where $v_B$ is related by an infinite re-scaling to the `physical Higgs condensate' $v_R$ defined through $\frac{d^2 V_{\rm eff}}{d ϕ^2_R}|_{ϕ_R= \pm v_R}=M^2_h$. New lattice data collected around the phase transition confirm this scenario. By denoting $M_{\rm SB} \equiv M_h ={\cal O} (v_R)$ the scale of the broken phase, our results suggest the existence of a `hierarchy' of scales $Γ_2(0) \ll M^2_{\rm SB} \ll v^2_B$ that become infinitely far in the continuum limit. This may open unexpected possibilities to reconcile an infinitesimal slope of the effective potential with finite values of $M_h$ and accomodate very different mass scales in the framework of a spontaneously broken theory.

hep-ph↗