Constraints on extended Bekenstein models from cosmological, astrophysical, and local data

Abstract

Searching for variations of nature's fundamental constants is a crucial step in our quest to go beyond our current standard model of fundamental physics. If they exist, such variations will be very likely driven by the existence of a new fundamental field. The Bekenstein model and its extensions introduce such a scalar field in a purely phenomenological way, inducing a variation of the fine-structure constant on cosmological scales. This theoretical framework is as simple and general as possible while still preserving all the symmetries of standard quantum electrodynamics. When allowing for couplings to the other sectors of the Universe, such as baryons, dark matter, and the cosmological constant, the Bekenstein model is expected to reproduce the low energy limits of several grand unification, quantum gravity, and higher dimensional theories. In this work, we constrain different versions of the Bekenstein model by confronting the full cosmological evolution of the field with an extensive set of astrophysical, cosmological, and local measurements. We show that couplings of the order of parts per million are excluded for all the cases considered, imposing strong restrictions on theoretical frameworks aiming to deal with variations of the fine-structure constant.

News from the Swampland — constraining string theory with astrophysics and cosmology

“…As such, by constraining the differential acceleration of two nearby geodesics, η, it is possible to bound the possible values for ζ [130][131][132]. Typically, in our case, one expects η ∼ O(10 −4 −10 −3 )ζ 2 , such that the latest MICROSCOPE bound η = (−1.5 ± 2.7) • 10 −15 [133] would be less constraining than atomic clocks (as also put forward in [94] for the so-called BSBM model, and in [90] for an ultra-light scalar). 15 However, the non-observation of a differential acceleration puts another independent constraint on any coupling.…”

“…(2.4). Such a term naturally preserves the U(1) gauge symmetry of the theory, and has been adopted in the past in the context of the Bekenstein model [92,93] (we explored such coupled models in detail in [94], using a similar methodology as the present paper). In such a framework, the fine structure constant α = e 2 /4π is not a constant anymore, and varies with the field as…”

“…(2.18), where we assume for simplicity a constant coupling ζ. The time-variations of the fine structure constant α(z) are then self-consistently propagated to all parts of the code, such as for example during recombination (building on our previous analysis in [94,97,98] and made publicly available in the class software), and are used as an output when combining with the data on α(z) or α(z) that is described below.…”

“…(2.18). Our dataset -detailed in [94,115] -contains more than 300 measurements obtained by the VLT-UVES and Keck-HIRES instruments, as well as points obtained from the HARPS, Subaru and ESPRESSO spectrograph, spanning a redshift range of 0.22 ≤ z ≤ 4.18 [116][117][118].…”

Runaway dilaton models: improved constraints from the full cosmological evolution

“…The present work builds upon several previous phenomenological studies [11][12][13][14] while aiming to be more accurate and more general. This is achieved by confronting the full cosmological field evolution with the latest datasets, as done in [15] for Bekenstein models, while freeing ourselves from assumptions made in previous studies. In section II we introduce the evolution equations of the coupled dilaton field, as well as their impact on various observables.…”