Science with a 16 m VLT: The Case for Variability of Fundamental Constants

Abstract

Only astronomical observations can effectively probe in space-time the variability of the physical dimensionless constants such as the fine structure constant α and proton-to-electron mass ratio, µ, which are related to fundamental forces of nature. Several theories beyond the Standard Model (SM) allow fundamental constants to vary, but they cannot make quantitative predictions so that only laboratory experiments and astronomical observations can show if this is the case or set the allowed bounds. At the moment of writing there are claims for a variability of both α and µ at 5 and 4 σ of C.L., respectively, although for α they are contrasted by null results. The observations are challenging and a new spectrograph such as ESPRESSO at the combined incoherent focus of 4 VLT units (a potential 16 m equivalent telescope) will allow for a significant improvement in the precision measurement clearing up the controversy. If the variations will be confirmed, the implications are far reaching, revealing new physics beyond the SM and pointing a direction for GUTs theories. A most exciting possibility is that a variation of α is induced by quintessence through its coupling with the electromagnetic field. If this is the case an accurate measurement of the variability could provide a way for reconstructing the equation of state of Dark Energy [1]. IntroductionThe Standard Model (SM) of particle physics needs 26 dimensionless physical constants for the description of the natural world ([18]), of these few are directly related to the strength of fundamental forces. Among them the fine structure constant (α = e 2 /(hc)) and the proton-to-electron mass ratio, (µ = m p /m e ) are of particular interest for us since they can be measured accurately by astronomical observations of intervening absorption systems towards distant QSOs. The fine structure constant α is related to the strength

ESPRESSO@VLT -- On-sky performance and first results

“…These facts were recognized by the ESO-ESA working group report on extrasolar planets in 2005 who emphasized the need of HARPS-like instruments on large telescopes (Perryman et al 2005). Simultaneously, the idea of a HARPS-like instrument for the VLT was directly derived from the CODEX project (Pasquini et al 2005;Molaro et al 2006;Molaro 2009), a phase-A study for the development of an ultra high-precision spectrograph for the European ELT, and presented by Pasquini et al (2009) in 2007 at the conference Science with the VLT in the ELT Era. Following this idea, ESO's Scientific-Technical Committee (STC) recommended in October 2007 the development of second-generation VLT instruments, and this proposal was endorsed by the ESO Council in December of the same year.…”

Chromatic drift of the Espresso Fabry-Pérot etalon

“…Here, we present a very similar study of the Fabry-Pérot etalon of the Echelle SPectrograph for Rocky Exoplanets and Stable Spectroscopic Observations (Espresso, Molaro 2009;Pepe et al 2010Pepe et al , 2014Pepe et al , 2021 installed at the incoherently combined Coundé focus of the ESO Very Large Telescope. Espresso has been in regular operation since November 2018.…”

Fundamental physics with ESPRESSO: Precise limit on variations in the fine-structure constant towards the bright quasar HE 0515−4414

“…The new high-resolution spectrograph at the VLT, ESPRESSO (Echelle SPectrograph for Rocky Exoplanet and Stable Spectroscopic Observations; Pepe et al 2021), was specifically designed to suppress wavelength calibration errors in quasar absorption measurements of α (Molaro et al 2006;Molaro 2009). ESPRESSO is fed by optical fibres, is sealed in a stable vacuum vessel with temperature control at the mK level, and can be calibrated with an 'astrocomb' -a femtosecond-pulsed laser frequency comb (LFC) with secondary mode filtering adapted to ESPRESSO's resolving power.…”