Bekenstein-type Model Research Articles

Current and future constraints on extended Bekenstein-type models for a varying fine-structure constant

There is a growing interest in astrophysical tests of the stability of dimensionless fundamental couplings, such as the fine-structure constant $\ensuremath{\alpha}$, as an optimal probe of new physics. The imminent arrival of the ESPRESSO spectrograph will soon enable significant gains in the precision and accuracy of these tests and widen the range of theoretical models that can be tightly constrained. Here we illustrate this by studying proposed extensions of the Bekenstein-type models for the evolution of $\ensuremath{\alpha}$ that allow different couplings of the scalar field to both dark matter and dark energy. We use a combination of current astrophysical and local laboratory data (from tests with atomic clocks) to show that these couplings are constrained to parts per million level, with the constraints being dominated by the atomic clocks. We also quantify the expected improvements from ESPRESSO and other future spectrographs, and briefly discuss possible observational strategies, showing that these facilities can improve current constraints by more than an order of magnitude.

Current and future constraints on Bekenstein-type models for varying couplings

Astrophysical tests of the stability of dimensionless fundamental couplings, such as the fine-structure constant $\alpha$ and the proton-to-electron mass ratio $\mu$, are an optimal probe of new physics. There is a growing interest in these tests, following indications of possible spacetime variations at the few parts per million level. Here we make use of the latest astrophysical measurements, combined with background cosmological observations, to obtain improved constraints on Bekenstein-type models for the evolution of both couplings. These are arguably the simplest models allowing for $\alpha$ and $\mu$ variations, and are characterized by a single free dimensionless parameter, $\zeta$, describing the coupling of the underlying dynamical degree of freedom to the electromagnetic sector. In the former case we find that this parameter is constrained to be $|\zeta_\alpha|<4.8\times10^{-6}$ (improving previous constraints by a factor of 6), while in the latter (which we quantitatively compare to astrophysical measurements for the first time) we find $\zeta_\mu=(2.7\pm3.1)\times10^{-7}$; both of these are at the $99.7\%$ confidence level. For $\zeta_\alpha$ this constraint is about 20 times stronger than the one obtained from local Weak Equivalence Principle tests, while for $\zeta_\mu$ it is about 2 orders of magnitude weaker. We also discuss the improvements on these constraints to be expected from the forthcoming ESPRESSO and ELT-HIRES spectrographs, conservatively finding a factor around 5 for the former and around 50 for the latter.

Fine-structure constant constraints on Bekenstein-type models

Astrophysical tests of the stability of dimensionless fundamental couplings, such as the fine-structure constant $\alpha$, are an area of much increased recent activity, following some indications of possible spacetime variations at the few parts per million level. Here we obtain updated constraints on the Bekenstein-Sandvik-Barrow-Magueijo model, which is arguably the simplest model allowing for $\alpha$ variations. Recent accurate spectroscopic measurements allow us to improve previous constraints by about an order of magnitude. We briefly comment on the dependence of the results on the data sample, as well as on the improvements expected from future facilities.

Coupling dark energy with standard model states

In this contribution one examines the coupling of dark energy to the gauge fields to neutrinos, and to the Higgs field. In the first case, one show how a putative evolution of the fundamental couplings of strong and weak interactions via coupling to dark energy through a generalized Bekenstein-type model may cause deviation on the statistical nuclear decay Rutherford-Soddy law. Existing bounds for the weak interaction exclude any significant deviation. For neutrinos, a perturbative approach is developed which allows for considering viable varying mass neutrino models coupled to any quintessence-type field. The generalized Chaplygin model is considered as an example. For the coupling with the Higgs field one obtains an interesting cosmological solution which includes the unification of dark energy and dark matter.

Dark energy and the Rutherford–Soddy radiative decay law

It is shown that a putative evolution of the fundamental couplings of strong and weak interactions via coupling to dark energy through a generalized Bekenstein-type model may, for a linear model of variation, cause deviations on the statistical nuclear decay Rutherford–Soddy law unless bounds are imposed on the parameters of this variation. Existing bounds for the weak interaction exclude any significant deviation. Bounds on the strong interaction are much less stringent.

GRAVITATIONAL EFFECTS OF VARYING ALPHA STRINGS

We study spatial variations of the fine-structure constant in the presence of static straight cosmic strings in the weak-field approximation in Einstein gravity. We work in the context of a generic Bekenstein-type model and consider a gauge kinetic function linear in the scalar field. We determine an analytical form for the scalar field and the string metric at large distances from the core. We show that the gravitational effects of α-varying strings can be seen as a combination of the gravitational effects of global and local strings. We also verify that at large distances to the core the space–time metric is similar to that of a global string. We study the motion of test particles approaching from infinity and show that photons are scattered to infinity while massive particles are trapped in bounded trajectories. We also calculate an overall limit on the magnitude of the variation of α for a GUT string, by considering suitable cosmological constraints coming from the Equivalence Principle.

Cosmic strings in Bekenstein-type models

We study static cosmic string solutions in the context of Bekenstein-type models. We showthat there is a class of models of this type for which the classical Nielsen–Olesen vortex isstill a valid solution. However, in general, static string solutions in Bekenstein-type modelsstrongly depart from the standard Nielsen–Olesen solution with the electromagnetic energyconcentrated along the string core seeding spatial variations of the fine structure constant,α. We consider models with a generic gauge kinetic function and show that theequivalence principle constraints impose tight limits on the allowed variations ofα induced by string networks on cosmological scales.