arXiv subjects

L. Campanelli

Publications and source records attributed to L. Campanelli.

At least 19 recordsLinked to original sources

arXiv2020

Can the Blackett conjecture directly account for the magnetic fields of celestial bodies and galaxies? And, is a lab-based test for the Blackett conjecture feasible?

According to the Blackett conjecture, any neutral rotating body acquires a magnetic moment proportional to its angular momentum. Using the data on the dipolar magnetic field of Mars, we put a stringent upper limit on the value of the Blackett's constant, the dimensionless constant that relates the magnetic moment to the angular momentum. As a consequence, the Blackett effect cannot directly account for the magnetic fields of celestial bodies and galaxies. We also show that the Blackett effect cannot be tested in a laboratory since the magnetic moment of any rotating lab-scale object would be much smaller than the one produced by the well-known Barnett effect.

physics.gen-ph↗

arXiv2016

Smooth magnetogenesis

In the Ratra scenario of inflationary magnetogenesis, the kinematic coupling between the photon and the inflaton undergoes a nonanalytical jump at the end of inflation. Using smooth interpolating analytical forms of the coupling function, we show that such unphysical jump does not invalidate the main prediction of the model, which still represents a viable mechanism for explaining cosmic magnetization. Nevertheless, there is a spurious result associated with the nonanaliticity of the coupling, to wit, the prediction that the spectrum of created photons has a power-law decay in the ultraviolet regime. This issue is discussed using both semiclassical approximation and smooth coupling functions.

astro-ph.CO↗

arXiv2012

Galaxy cluster number count data constraints on cosmological parameters

[Abridged] We use data on massive galaxy clusters ($M_{\rm cluster} > 8 \times 10^{14} h^{-1} M_\odot$ within a comoving radius of $R_{\rm cluster} = 1.5 h^{-1}\Mpc$) in the redshift range $0.05 \lesssim z \lesssim 0.83$ to place constraints, simultaneously, on the nonrelativistic matter density parameter $Ω_m$, on the amplitude of mass fluctuations $σ_8$, on the index $n$ of the power-law spectrum of the density perturbations, and on the Hubble constant $H_0$, as well as on the equation-of-state parameters $(w_0,w_a)$ of a smooth dark energy component. For the first time, we properly take into account the dependence on redshift and cosmology of the quantities related to cluster physics: the critical density contrast, the growth factor, the mass conversion factor, the virial overdensity, the virial radius and, most importantly, the cluster number count derived from the observational temperature data. We show that, contrary to previous analyses, cluster data alone prefer low values of the amplitude of mass fluctuations, $σ_8 \leq 0.69 (1σC.L.)$, and large amounts of nonrelativistic matter, $Ω_m \geq 0.38 (1σC.L.)$, in slight tension with the $Λ$CDM concordance cosmological model, though the results are compatible with $Λ$CDM at $2σ$. In addition, we derive a $σ_8$ normalization relation, $σ_8 Ω_m^{1/3} = 0.49 \pm 0.06 (2σC.L.)$.

astro-ph.CO↗

arXiv2011

Cosmic Parallax in Ellipsoidal Universe

The detection of a time variation of the angle between two distant sources would reveal an anisotropic expansion of the Universe. We study this effect of "cosmic parallax" within the "ellipsoidal universe" model, namely a particular homogeneous anisotropic cosmological model of Bianchi type I, whose attractive feature is the potentiality to account for the observed lack of power of the large-scale cosmic microwave background anisotropy. The preferred direction in the sky, singled out by the axis of symmetry inherent to planar symmetry of ellipsoidal universe, could in principle be constrained by future cosmic parallax data. However, that will be a real possibility if and when the experimental accuracy will be enhanced at least by two orders of magnitude.

astro-ph.CO↗

arXiv2011

Anisotropic dark energy and ellipsoidal universe

A cosmological model with anisotropic dark energy is analyzed. The amount of deviation from isotropy of the equation of state of dark energy, the skewness δ, generates an anisotropization of the large-scale geometry of the Universe, quantifiable by means of the actual shear Σ_0. Requiring that the level of cosmic anisotropization at the time of decoupling is such to solve the "quadrupole problem" of cosmic microwave background radiation, we find that |δ| \sim 10^{-4} and |Σ_0| \sim 10^{-5}, compatible with existing limits derived from the magnitude-redshift data on type Ia supernovae.

astro-ph.CO↗

arXiv2011

Testing the Isotropy of the Universe with Type Ia Supernovae

We analyze the magnitude-redshift data of type Ia supernovae included in the Union and Union2 compilations in the framework of an anisotropic Bianchi type I cosmological model and in the presence of a dark energy fluid with anisotropic equation of state. We find that the amount of deviation from isotropy of the equation of state of dark energy, the skewness δ, and the present level of anisotropy of the large-scale geometry of the Universe, the actual shear Σ_0, are constrained in the ranges -0.16 < δ< 0.12 and -0.012 < Σ_0 < 0.012 (1σC.L.) by Union2 data. Supernova data are then compatible with a standard isotropic universe (δ= Σ_0 = 0), but a large level of anisotropy, both in the geometry of the Universe and in the equation of state of dark energy, is allowed.

astro-ph.CO↗

arXiv2009

Lorentz Symmetry Violation and Galactic Magnetism

We analyze the generation of primordial magnetic fields during de Sitter inflation in a Lorentz-violating theory of Electrodynamics containing a Chern-Simons term which couples the photon to an external four-vector. We find that, for appropriate magnitude of the four-vector, the generated field is maximally helical and, through an inverse cascade caused by turbulence of primeval plasma, reaches at the time of protogalactic collapse an intensity and correlation length such as to directly explain galactic magnetism.

astro-ph↗

arXiv2009

Spinning Supersymmetric Q-balls

We construct nontopological solitonic solutions in (3+1)-dimensional Minkowski spacetime carrying a conserved global U(1) charge and nonvanishing angular momentum in a supersymmetric extension of the standard model with low-energy, gauge-mediated symmetry breaking.

hep-th↗

arXiv2009

Maxwell-Kostelecký Electromagnetism and Cosmic Magnetization

The Lorentz violating term in the photon sector of Standard Model Extension, $\mathcal{L}_K = -{$\frac14$} (k_F)_{αβμν} F^{αβ} F^{μν}$ (here referred to as the Kostelecký term), breaks conformal invariance of electromagnetism and enables a superadiabatic amplification of magnetic vacuum fluctuations during inflation. For a wide range of values of parameters defining Lorentz symmetry violation and inflation, the present-day magnetic field can have an intensity of order of nanogauss on megaparsec scales and then could explain the large-scale magnetization of the universe.

astro-ph↗

arXiv2008

Inflation-Produced Magnetic Fields in R^n F^2 and I F^2 models

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.

astro-ph↗

arXiv2007

Supersymmetric Q-balls: A Numerical Study

We study numerically a class of non-topological solitons, the Q-balls, arising in supersymmetric extension of the Standard Model with low-energy, gauge-mediated symmetry breaking. % Taking into account the exact form of the supersymmetric potential giving rise to Q-balls, we find that there is a lower limit on the value of the charge $Q$ in order to make them classically stable: $Q \gtrsim 5 \times 10^2 Q_{\rm cr}$, where $Q_{\rm cr}$ is constant depending on the parameters defining the potential and can be in the range $1 \lesssim Q_{\rm cr} \lesssim 10^{8 ÷16}$.If $Q$ is the baryon number, stability with respect to the decay into protons requires $Q \gtrsim 10^{17} Q_{\rm cr}$, while if the gravitino mass is greater then $m_{3/2} \gtrsim 61 \MeV$, no stable gauge-mediation supersymmetric Q-balls exist. Finally, we find that energy and radius of Q-balls can be parameterized as $E \sim ξ_E Q^{3/4}$ and $R \sim ξ_R Q^{1/4}$, where $ξ_E$ and $ξ_R$ are slowly varying functions of the charge.

hep-th↗

arXiv2007

Inflation-Produced Magnetic Fields in Nonlinear Electrodynamics

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.

astro-ph↗

arXiv2007

Cosmic Microwave Background Quadrupole and Ellipsoidal Universe

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.

astro-ph↗

arXiv2007

Time Variation of the Fine Structure Constant in the Spacetime of a Domain Wall

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.

astro-ph↗

arXiv2006

A Note on the Cosmic Evolution of the Axion in a Strong Magnetic Field

It has been pointed out in the literature that in the presence of an external magnetic field the axion mass receives an electromagnetic contribution. We show that if a magnetic field with energy density larger than ~10^{-8} times the energy density of the Universe existed at temperatures of a few GeV, that contribution would be dominant and consequently the cosmic evolution of the axion field would change substantially. In particular, the expected axion relic abundance would be lowered, allowing a small relaxation of the present cosmological bound on the Peccei-Quinn constant.

astro-ph↗

arXiv2006

Ellipsoidal Universe Can Solve The CMB Quadrupole Problem

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.

astro-ph↗

arXiv2006

Magnetic Induced Axion Mass

We study the effect of a uniform magnetic field on the dynamics of axions. In particular, we show that the Peccei-Quinn symmetry is explicitly broken by the presence of an external magnetic field. This breaking is induced by the non-conservation of the magnetic helicity and generates an electromagnetic contribution to the axion mass. We compute the magnetic axion mass in one loop approximation, with no restriction on the intensity of the magnetic field, and including thermal effects.

hep-ph↗

arXiv2006

Production of Axions by Cosmic Magnetic Helicity

We investigate the effects of an external magnetic helicity production on the evolution of the cosmic axion field. It is shown that a helicity larger than (few \times 10^{-15} G)^2 Mpc, if produced at temperatures above a few GeV, is in contradiction with the existence of the axion, since it would produce too much of an axion relic abundance.

astro-ph↗