Fundamental cosmology from precision spectroscopy: Varying couplings

The observational evidence for the 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. Forthcoming high-resolution ultrastable spectrographs will play a crucial role in this quest for new physics, by enabling a new generation of precision consistency tests. Here we focus on astrophysical tests of the stability of nature’s fundamental couplings, and by using principal component analysis techniques further calibrated by existing VLT data we discuss how the improvements that can be expected with ESPRESSO and ELT-HIRES will impact on fundamental cosmology. In particular we show that a 20 to 30 night program on ELT-HIRES will allow it to play a leading role in fundamental cosmology.

Figure 1

Observation time and SNR for the VLT absorbers of [25], as a function of the quasar magnitude. Circles denote absorbers yielding measurements with better than 10 ppm statistical uncertainty, and crosses denote the rest of the absorbers.

Figure 2

Observation time and SNR for the VLT absorbers of [25], as a function of the redshift of the absorption system. Circles denote absorbers yielding measurements with better than 10 ppm statistical uncertainty, and crosses denote the rest of the absorbers.

Figure 3

Uncertainty in the $\alpha$ measurements for the VLT absorbers of [25], as a function of the magnitude of the quasar and the redshift of the absorbers. Circles denote absorbers yielding measurements with better than 10 ppm statistical uncertainty, and crosses denote the rest of the absorbers.

Figure 4

Correlation between statistical uncertainty of each of the $\alpha$ measurements and the number of transitions used to obtain them. Each point in the plot was obtained as an average of the various points in the data set with each number of transitions used. The red line is the best polynomial fit, discussed in the text.

Figure 5

Top: Distribution of uncertainties in $\alpha$ for 20-source VLT subsamples, for a total of 15000 realizations. Bottom: Values of the effective parameter $C$ as a function of the number of systems considered, for the parametrization of the observational formula applied to the current UVES data. The red line is the best linear fit, discussed in the text.

Figure 6

The uncertainty in the best-determined PCA model in the baseline scenario described in the main text, as a function of the number of nights of observation and absorbers measured, respectively, for the constant, step and bump fiducial models (top to bottom). In each case the color map indicates the logarithm of the uncertainty.

Figure 7

The uncertainty in the best-determined PCA mode in the three scenarios discussed in the main text, for each of the fiducial models considered. The top (black), middle (red) and bottom (blue) sets of three lines correspond to the baseline, ESPRESSO and ELT-HIRES cases, respectively. In each set the solid, dashed and dotted lines, respectively, correspond to the constant, step and bump fiducial models.