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Daniele S. M. Alves

Publications and source records attributed to Daniele S. M. Alves.

26 records · Page 2Linked to original sources
arXiv2010

The Poker Face of Inelastic Dark Matter: Prospects at Upcoming Direct Detection Experiments

The XENON100 and CRESST experiments will directly test the inelastic dark matter explanation for DAMA's 8.9? sigma anomaly. This article discusses how predictions for direct detection experiments depend on uncertainties in quenching factor measurements, the dark matter interaction with the Standard Model and the halo velocity distribution. When these uncertainties are accounted for, an order of magnitude variation is found in the number of expected events at CRESST and XENON100.

hep-ph↗
arXiv2010

Composite Inelastic Dark Matter

Peaking consistently in June for nearly eleven years, the annual modulation signal reported by DAMA/NaI and DAMA/LIBRA offers strong evidence for the identity of dark matter. DAMA's signal strongly suggest that dark matter inelastically scatters into an excited state split by O(100 keV). We propose that DAMA is observing hyperfine transitions of a composite dark matter particle. As an example, we consider a meson of a QCD-like sector, built out of constituent fermions whose spin-spin interactions break the degeneracy of the ground state. An axially coupled U(1) gauge boson that mixes kinetically with hypercharge induces inelastic hyperfine transitions of the meson dark matter that can explain the DAMA signal.

hep-ph↗
arXiv2010

The Cosmology of Composite Inelastic Dark Matter

Composite dark matter is a natural setting for implementing inelastic dark matter - the O(100 keV) mass splitting arises from spin-spin interactions of constituent fermions. In models where the constituents are charged under an axial U(1) gauge symmetry that also couples to the Standard Model quarks, dark matter scatters inelastically off Standard Model nuclei and can explain the DAMA/LIBRA annual modulation signal. This article describes the early Universe cosmology of a minimal implementation of a composite inelastic dark matter model where the dark matter is a meson composed of a light and a heavy quark. The synthesis of the constituent quarks into dark mesons and baryons results in several qualitatively different configurations of the resulting dark matter hadrons depending on the relative mass scales in the system.

hep-ph↗
arXiv2009

Experimental constraints on the free fall acceleration of antimatter

In light of recent experimental proposals to measure the free fall acceleration of antihydrogen in the earth's gravitational field, we investigate the bounds that existing experiments place on any asymmetry between the free fall of matter and antimatter. We conclude that existing experiments constrain any such asymmetry to be less than about 10^-7. First we consider contributions to the inertial masses of atoms that encode the presence of antimatter and use precision Eotvos experiments to establish the level at which they satisfy the equivalence principle. In particular we focus on vacuum polarization effects and the antiquark content of nucleons. Second we consider a class of theories that contain long range scalar and vector forces that cancel with one another to some high precision. By construction such theories would be able to evade detection in Eotvos experiments that utilize matter while still allowing for a signal in antimatter experiments. Even taking such cancellation for granted, however, we show that the radiative damping of binary pulsar systems constrains these forces to be significantly weaker than gravity. Furthermore we show that there are limits to the accuracy with which such cancellation can be arranged: first by determining the precision to which scalar charges can track vector charges in the best candidate theories; and, second, by showing that the different velocity dependence of scalar and vector forces necessarily introduces non-cancellation at a quantifiable level.

hep-ph↗
arXiv2004

Acceleration field of a Universe modeled as a mixture of scalar and matter fields

A model of the Universe as a mixture of a scalar (inflaton or rolling tachyon from the string theory) and a matter field (classical particles) is analyzed. The particles are created at the expense of the gravitational energy through an irreversible process whereas the scalar field is supposed to interact only with itself and to be minimally coupled with the gravitational field. The irreversible processes of particle creation are related to the non-equilibrium pressure within the framework of the extended (causal or second-order) thermodynamic theory. The scalar field (inflaton or tachyon) is described by an exponential potential density added by a parameter which represents its asymptotic value and can be interpreted as the vacuum energy. This model can simulate three phases of the acceleration field of the Universe, namely,(a) an inflationary epoch with a positive acceleration followed by a decrease of the acceleration field towards zero, (b) a past decelerated period where the acceleration field decreases to a maximum negative value followed by an increase towards zero, and (c) a present accelerated epoch. For the energy densities there exist also three distinct epochs which begin with a scalar field dominated period followed by a matter field dominated epoch and coming back to a scalar field dominated phase.

gr-qc↗
arXiv2004

Applications to cosmological models of a complex scalar field coupled to a U(1) vector gauge field

We consider the Abelian model of a complex scalar field coupled to a gauge field within the framework of General Relativity and search for cosmological solutions. For this purpose we assume a homogeneous, isotropic and uncharged Universe and a homogeneous scalar field. This model may be inserted in several contexts in which the scalar field might act as inflaton or quintessence, whereas the gauge field might play the role of radiation or dark matter, for instance. Particularly, we propose two such models: (i) in the first, the inflaton field decays to massive vector bosons that we regard as dark-matter; (ii) in the second, due to its coupling to radiation the scalar field is displaced from its ground state and drives an accelerated expansion of the Universe, playing the role of quintessence. We observe that the equations are quite simplified and easier to be solved if we assume a roughly monochromatic radiation spectrum.

astro-ph↗
arXiv2004

Palatini approach to 1/R gravity and its implications to the late Universe

By applying the Palatini approach to the 1/R-gravity model it is possible to explain the present accelerated expansion of the Universe. Investigation of the late Universe limiting case shows that: (i) due to the curvature effects the energy-momentum tensor of the matter field is not covariantly conserved; (ii) however, it is possible to reinterpret the curvature corrections as sources of the gravitational field, by defining a modified energy-momentum tensor; (iii) with the adoption of this modified energy-momentum tensor the Einstein's field equations are recovered with two main modifications: the first one is the weakening of the gravitational effects of matter whereas the second is the emergence of an effective varying "cosmological constant"; (iv) there is a transition in the evolution of the cosmic scale factor from a power-law scaling $a\propto t^{11/18}$ to an asymptotically exponential scaling $a\propto \exp(t)$; (v) the energy density of the matter field scales as $ρ_m\propto (1/a)^{36/11}$; (vi) the present age of the Universe and the decelerated-accelerated transition redshift are smaller than the corresponding ones in the $Λ$CDM model.

gr-qc↗