The status of varying constants: a review of the physics, searches and implications

Abstract

Abstract. The observational evidence for the recent acceleration of the universe demonstrates that canonical theories of cosmology and particle physics are incomplete-if not incorrect-and that new physics is out there, waiting to be discovered. A key task for the next generation of laboratory and astrophysical facilities is to search for, identify and ultimately characterize this new physics. Here we highlight recent developments in tests of the stability of nature's fundamental couplings, which provide a direct handle on new physics: a detection of variations will be revolutionary, but even improved null results provide competitive constraints on a range of cosmological and particle physics paradigms. A joint analysis of all currently available data shows a preference for variations of α and µ at about the two-sigma level, but inconsistencies between different sub-sets (likely due to hidden systematics) suggest that these statistical preferences need to be taken with caution. On the other hand, these measurements strongly constrain Weak Equivalence Principle violations. Plans and forecasts for forthcoming studies with facilities such as ALMA, ESPRESSO and the ELT, which should clarify these issues, are also discussed, and synergies with other probes are briefly highlighted. The goal is to show how a new generation of precision consistency tests of the standard paradigm will soon become possible.PACS numbers: 98.80.Es, 95.36.+x, 98.62.Ra,

Distinguishing freezing and thawing dark energy models through measurements of the fine-structure constant

“…As is physically clear, the relevant parameter in the cosmological evolution is the field displacement relative to its present-day value, implying that we can set φ 0 to zero without loss of generality. In these models the proton and neutron masses are also expected to vary due to the electromagnetic corrections of their masses; while we do not discuss this in detail in the present work -detailed discussions can be found elsewhere (Uzan 2011;Martins 2017) -one relevant consequence of this fact is that local tests of the equivalence principle also constrain these models. A varying α violates the Einstein equivalence principle since it clearly violates local position invariance.…”

De Sitter vs Quintessence in String Theory

“…V (χ, ) = e K (χ, ) (|D χ W| 2 + |D W| 2 − 3|W| 2 ). (27) where χ is the quintessence field and collectively denotes matter fields 13 . In this context the most one can do to isolate the quintessence field φ from matter fields i.e.…”

“…By choosing the value of the quintessence field χ today to be χ 0 = 0 one can of course avoid fifth-force bounds today. However, for a quintessence potential of the formV (χ ) = 4 e −kχ with k O(1), the quintessence field is expected to move a distance φ ∼ O(1)M p and so at some point before the transition in the past to a matter/radiation dominated phase one would have had 13 Notice that this example does not contain the case of [152] which we shall review in Sec. 3.3.…”

“…[9][10][11] In particular it implies that at present we are necessarily in an epoch of quintessence. The tight bounds on fifthforces [12] and the time variation of fundamental constants, [13] provide strong constraints on the couplings of the quintessence field. Furthermore, in the context of N = 1 supergravity it seems very hard to be able to decouple a quintessence field from the Standard Model.…”

Distorted neutrino oscillations from time varying cosmic fields

“…(5) and (6). If the scalar oscillation period τ ϕ ≡ 2π=m ϕ is longer than the characteristic neutrino time of flight T ν , but shorter than the total experimental run time, then neutrinos emitted at different times will sample different values of ϕ over the course of a given experiment.…”