arXiv subjects
Publications and source records attributed to P. Cea.
We test the method of analytic continuation from imaginary to real chemical potential in two-color QCD, which is free from the sign problem. In particular, we consider the analytic continuation of the critical line to real values of the chemical potential.
We re-analyze the production of seed magnetic fields during Inflation in (R/m^2)^n F_{μν}F^{μν} and I F_{μν}F^{μν} models, where n is a positive integer, R the Ricci scalar, m a mass parameter, and I \propto η^αa power-law function of the conformal time η, with αa positive real number. If m is the electron mass, the produced fields are uninterestingly small for all n. Taking m as a free parameter we find that, for n \geq 2, the produced magnetic fields can be sufficiently strong in order to seed dynamo mechanism and then to explain galactic magnetism. For α\gtrsim 2, there is always a window in the parameters defining Inflation such that the generated magnetic fields are astrophysically interesting. Moreover, if Inflation is (almost) de Sitter and the produced fields almost scale-invariant (α\simeq 4), their intensity can be strong enough to directly explain the presence of microgauss galactic magnetic fields.
We study the generation of primeval magnetic fields during inflation era in nonlinear theories of electrodynamics. Although the intensity of the produced fields strongly depends on characteristics of inflation and on the form of electromagnetic Lagrangian, our results do not exclude the possibility that these fields could be astrophysically interesting.
Recent Wilkinson Microwave Anisotropy Probe (WMAP) data confirm the Cosmic Microwave Background (CMB) quadrupole anomaly. We further elaborate our previous proposal that the quadrupole power can be naturally suppressed in axis-symmetric universes. In particular, we discuss in greater detail the CMB quadrupole anisotropy and considerably improve our analysis. As a result, we obtain tighter constraints on the direction of the axis of symmetry as well as on the eccentricity at decoupling. We find that the quadrupole amplitude can be brought in accordance with observations with an eccentricity at decoupling of about 0.35 10^{-2}. Moreover, our determination of the direction of the symmetry axis is in reasonable agreement with recent statistical analyses of cleaned CMB temperature fluctuation maps obtained by means of improved internal linear combination methods as Galactic foreground subtraction technique.
The gravitational field produced by a domain wall acts as a medium with spacetime-dependent permittivity ε. Therefore, the fine structure constant α= e^2/4 πεwill be a time-dependent function at fixed position. The most stringent constraint on the time-variation of αcomes from the natural reactor Oklo and gives |\dotα/α| < few 10^{-17} yr^{-1}. This limit constrains the tension of a cosmic domain wall to be less than σ\lesssim 10^{-2} MeV^3, and then represents the most severe limit on the energy density of a cosmic wall stretching our Universe.
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.
The recent three-year WMAP data have confirmed the anomaly concerning the low quadrupole amplitude compared to the best-fit ΛCDM prediction. We show that, allowing the large-scale spatial geometry of our universe to be plane-symmetric with eccentricity at decoupling or order 10^{-2}, the quadrupole amplitude can be drastically reduced without affecting higher multipoles of the angular power spectrum of the temperature anisotropy.
We discuss a new mechanism which allows domain walls produced during the primordial electroweak phase transition. We show that the effective surface tension of these domain walls can be made vanishingly small due to a peculiar magnetic condensation induced by fermion zero modes localized on the wall. We find that in the perfect gas approximation the domain wall network behaves like a radiation gas. We consider the recent high-red shift supernova data and we find that the corresponding Hubble diagram is compatible with the presence in the Universe of a ideal gas of ferromagnetic domain walls. We show that our domain wall gas induces a completely negligible contribution to the large-scale anisotropy of the microwave background radiation.
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.
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.
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'.
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'.
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 $Λ$.
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.
In this paper we investigate Charged Domain Walls (CDW's), topological defects that acquire surface charge density $Q$ induced by fermion states localized on the walls. The presence of an electric and magnetic field on the walls is also discussed. We find a relation in which the value of the surface charge density $Q$ is connected with the existence of such topological defects.
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 $Λ$.
We investigate gravitational properties of thin planar wall solutions of the Einstein's equations in the weak field approximation. We find the general metric solutions and discuss the behavior of a particle placed initially at rest to one side of the plane. Moreover we study the case of non-reflection-symmetric solutions.
In this paper we discuss once more the zero mode contribution to the vacuum energy density. We show that a careful treatment of the zero modes leads to the conclusion that domain walls may be ferromagnetic, and could generate a magnetic field of cosmological interest.