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Eduard Masso

Publications and source records attributed to Eduard Masso.

At least 37 records · Page 2Linked to original sources
arXiv2005

Evading Astrophysical Constraints on Axion-Like Particles

Stellar energy loss arguments lead to strong constraints on the coupling $ϕγγ$ of a light axion-like particle to two photons. Helioscopes, like CAST, are able to put competitive bounds. The PVLAS experiment has recently observed a rotation of the polarization of a laser propagating in a magnetic field that can be interpreted as the effect of a quite strong $ϕγγ$ coupling. We present scenarios where the astrophysical and CAST bounds can be evaded, and we show that the PVLAS result can be accomodated in one of the models, provided the new physics scale is at very low energies.

hep-ph↗
arXiv2004

Planck-Scale Effects on Global Symmetries: Cosmology of Pseudo-Goldstone Bosons

We consider a model with a small explicit breaking of a global symmetry, as suggested by gravitational arguments. Our model has one scalar field transforming under a non-anomalous U(1) symmetry, and coupled lo matter and to gauge bosons. The spontaneous breaking of the explicitly broken symmetry gives rise to a massive pseudo-Goldstone boson. We analyze thermal and non-thermal production of this particle in the early universe, and perform a systematic study of astrophysical and cosmological constraints on its properties. We find that for very suppressed explicit breaking the pseudo-Goldstone boson is a cold dark matter candidate.

hep-ph↗
arXiv2004

Systematic Approach to Gauge-Invariant Relations between Lepton Flavor Violating Processes

We analyze four-lepton contact interactions that lead to lepton flavor violating processes, with violation of individual family lepton number but total lepton number conserved. In an effective Lagrangian framework, the assumption of gauge invariance leads to relations among branching ratios and cross sections of lepton flavor violating processes. In this paper, we work out how to use these relations systematically. We also study the consequences of loop-induced processes.

hep-ph↗
arXiv2004

On the Gravitational Field of Antimatter

The gravitational field of matter and that of antimatter could differ. This might be one signature of quantum gravity. We show that primordial Big Bang Nucleosynthesis restricts such a possibility.

astro-ph↗
arXiv2004

Neutrino magnetic moments and photo-disintegration of deuterium

Neutrinos with non-zero magnetic moments can dissociate deuterium nuclei by a photon exchange, in addition to the weak neutral current process. We calculate the neutrino-magnetic moment induced photo-dissociation cross section of deuterium using the equivalent photon method. This process would contribute extra events to the neutral current reaction which is observed with high precision in the salt-phase of SNO experiment. Using the SNO data and the recent laboratory measurements of the $^7 Be (p, γ) ^8 B$ reaction which give a more precise value of the solar $^8 B$ flux we find that the neutrino effective magnetic moment is $μ_{eff}^2 = (-2.76 \pm 1.46) \times 10^{-16} μ_B^2$ which can be interpreted as an upper bound $|μ_{eff}| < 3.71 \times 10^{-9} μ_B$ (at $95% CL$) on the neutrino magnetic moments.

hep-ph↗
arXiv2004

Axions

I review the physics of axions, paying attention to the role as dark matter. This paper is based on talks given at the workshops ``Thinking, Observing and Mining the Universe'' held in Sorrento (Italy), September 22-27, 2003, and at ``International Workshop on Astroparticle and High Energy Physics'' held in Valencia (Spain) October 14-18, 2003.

hep-ph↗
arXiv2002

Axions and Axion-like Particles

I review the theoretical motivation for the axion and present an update of the experimental status of axion searches. I finally comment on some aspects of the physics of axion-like particles.

hep-ph↗
arXiv2002

Primordial Helium Production in a Charged Universe

We use the constraints arising from primordial nucleosynthesis to bound a putative electric charge density $|e|n_q$ of the universe. We find $|n_q/n_γ| \lesssim 10^{-43}$, four orders of magnitude more stringent than previous limits. We also work out the bounds on $n_q$ in models with a photon mass, that allows to have a charge density without large-scale electric fields.

astro-ph↗
arXiv2002

On universality of the coupling of neutrinos to Z

We employ an effective Lagrangian approach and use LEP data to place severe bounds on universality violations of the couplings of $ν_e$, $ν_μ$, and $ν_τ$ to the $Z$ boson. Our results justify the assumption of universality in these couplings that is usually made, as for example in the analysis of solar neutrinos detected at SNO.

hep-ph↗
arXiv2002

On Axion Thermalization in the Early Universe

We reanalyze the conditions under which we have a primordial thermal population of axions. Compared with previous studies, we find other processes, involving gluons and quarks, that dominate at high temperatures. We conclude that if the Peccei-Quinn scale fulfills $F_a < 1.2 \times 10^{12} \GeV$ there is thermal axion production. In this case, a period in the early universe exists where axions interact with the QCD plasma and we point out that non-thermal axions produced before the end of this period will thermalize. This could lead to a reduction of the expected density of axions from string decay in models with $F_a < 1.2 \times 10^{12} \GeV$.

hep-ph↗
arXiv2002

Constraints on decay plus oscillation solutions of the solar neutrino problem

We examine the constraints on non-radiative decay of neutrinos from the observations of solar neutrino experiments. The standard oscillation hypothesis among three neutrinos solves the solar and atmospheric neutrino problems. Decay of a massive neutrino mixed with the electron neutrino results in the depletion of the solar neutrino flux. We introduce neutrino decay in the oscillation hypothesis and demand that decay does not spoil the successful explanation of solar and atmospheric observations. We obtain a lower bound on the ratio of the lifetime over the mass of $ν_2$, $(τ_2/m_2) > 22.7 (\srm/\MeV)$ for the MSW solution of the solar neutrino problem and $(τ_2/m_2) > 27.8 (\srm/\MeV)$ for the VO solution (at 99% C.L.).

hep-ph↗
arXiv2002

Summing the derivative expansion of the effective action

The derivative expansion of the effective action is a perturbative development in derivatives of the fields. The expansion breaks down when some of the derivatives are too large. We show how to sum exactly the first and second derivatives and treat perturbatively derivatives higher than second.

hep-th↗
arXiv2000

Neutrino-photon reactions for energies above $m_e$

We show that neutrino-photon reactions above $m_e$ are dominated by the reaction $νγ\to νe^+ e^-$. We calculate its cross-section and see that it is larger by several orders of magnitude than the cross-sections of other neutrino-photon processes, for energies above $m_e$. We also discuss potential astrophysical and cosmological consequences.

hep-ph↗
arXiv1999

Photon Spectrum Produced by the Late Decay of a Cosmic Neutrino Background

We obtain the photon spectrum induced by a cosmic background of unstable neutrinos. We study the spectrum in a variety of cosmological scenarios and also we allow for the neutrinos having a momentum distribution (only a critical matter dominated universe and neutrinos at rest have been considered until now). Our results can be helpful when extracting bounds on neutrino electric and magnetic moments from cosmic photon background observations.

astro-ph↗
arXiv1997

High Precision Tests of QED and Physics beyond the Standard Model

We study the four most significant high precision observables of QED ---the anomalous electron and muon magnetic moments, the hydrogen Lamb shift and muonium hyperfine splitting--- in the context of SU(2) x U(1) gauge-invariant effective Lagrangians. The agreement between the theoretical predictions for these observables and the experimental data places bounds on the lowest dimension operators of the effective Lagrangians. We also place bounds on such effective operators using other experimental data. Comparison of the tow types of bounds allows us to discuss the potential of each one of the four high precision observables in the search for physics beyond the Standard Model. We find that the anomalous electron and muon magnetic moments are sensitive to new physics while the hydrogen Lamb shift and muonium hyperfine splitting are not.

hep-ph↗