Astronomical constraints on the cosmic evolution of the fine structure constant and possible quantum dimensions

Varying Constants, Gravitation and Cosmology

Fundamental constants are a cornerstone of our physical laws. Any constant varying in space and/or time would reflect the existence of an almost massless field that couples to matter. This will induce a violation of the universality of free fall. Thus, it is of utmost importance for our understanding of gravity and of the domain of validity of general relativity to test for their constancy. We detail the relations between the constants, the tests of the local position invariance and of the universality of free fall. We then review the main experimental and observational constraints that have been obtained from atomic clocks, the Oklo phenomenon, solar system observations, meteorite dating, quasar absorption spectra, stellar physics, pulsar timing, the cosmic microwave background and big bang nucleosynthesis. At each step we describe the basics of each system, its dependence with respect to the constants, the known systematic effects and the most recent constraints that have been obtained. We then describe the main theoretical frameworks in which the low-energy constants may actually be varying and we focus on the unification mechanisms and the relations between the variation of different constants. To finish, we discuss the more speculative possibility of understanding their numerical values and the apparent fine-tuning that they confront us with.

Constraints on changes in fundamental constants from a cosmologically distant OH absorber or emitter

We have detected the four 18 cm OH lines from the z approximaetely 0.765 gravitational lens toward PMN J0134-0931. The 1612 and 1720 MHz lines are in conjugate absorption and emission, providing a laboratory to test the evolution of fundamental constants over a large lookback time. We compare the HI and OH main line absorption redshifts of the different components in the z approximately 0.765 absorber and the z approximately 0.685 lens toward B0218 + 357 to place stringent constraints on changes in F triple-bond g(p)[alpha(2)/mu](1.57). We obtain [DeltaF/F] = (0.44 +/- 0.36(stat) +/- 1.0(sys)t) x 10(-5), consistent with no evolution over the redshift range 0 < z < or = 0.7. The measurements have a 2sigma sensitivity of [Deltaalpha/alpha] < 6.7 x 10(-6) or [Deltamu/mu] < 1.4 x 10(-5) to fractional changes in alpha and mu over a period of approximately 6.5 G yr, half the age of the Universe. These are among the most sensitive constraints on changes in mu.

Limits on variations in fundamental constants from 21-cm and ultraviolet Quasar absorption lines

Quasar absorption spectra at 21-cm and UV rest wavelengths are used to estimate the time variation of x [triple-bond] alpha(2)g(p)mu, where alpha is the fine structure constant, g(p) the proton g factor, and m(e)/m(p) [triple-bond] mu the electron/proton mass ratio. Over a redshift range 0.24 < or = zeta(abs) < or = 2.04, (Deltax/x)(weighted)(total) = (1.17 +/- 1.01) x 10(-5). A linear fit gives x/x = (-1.43 +/- 1.27) x 10(-15) yr(-1). Two previous results on varying alpha yield the strong limits Deltamu/mu = (2.31 +/- 1.03) x 10(-5) and Deltamu/mu=(1.29 +/- 1.01) x10(-5). Our sample, 8 x larger than any previous, provides the first direct estimate of the intrinsic 21-cm and UV velocity differences 6 km s(-1).

Conjugate 18 cm OH satellite lines at a cosmological distance

We have detected the two 18 cm OH satellite lines from the z approximately 0.247 source PKS1413+135, the 1720 MHz line in emission and the 1612 MHz line in absorption. The 1720 MHz luminosity is L(OH) approximately 354L (center dot in circle), more than an order of magnitude larger than that of any other known 1720 MHz maser. The profiles of the two satellite lines are conjugate, implying that they arise in the same gas. This allows us to test for any changes in the values of fundamental constants without being affected by systematic uncertainties arising from relative motions between the gas clouds in which the different lines arise. Our data constrain changes in G identical with g(p)[alpha(2)/y](1.849), where y identical with m(e)/m(p); we find DeltaG/G=2.2+/-3.8 x 10(-5), consistent with no changes in alpha, g(p), and y.

Constraining the variation of fundamental constants using 18 cm OH lines

We describe a new technique to estimate variations in the fundamental constants using 18 cm OH absorption lines, with the advantage that all lines arise in the same species, allowing a clean comparison between the measured redshifts. In conjunction with one additional transition, it is possible to simultaneously measure changes in alpha, g(p), and y identical with m(e)/m(p). We use the 1665 and 1667 MHz line redshifts in conjunction with those of HI 21 cm and mm-wave molecular absorption in a gravitational lens at z approximately 0.68 to constrain changes in the three parameters over the redshift range 0<z less, similar 0.68. While the constraints are relatively weak ( less, similar 1 part in 10(3)), this is the first simultaneous constraint on the variation of all three parameters. Either one (or more) of alpha, g(p), and y must vary with cosmological time or there must be systematic velocity offsets between the OH, HCO+, and HI absorbing clouds.

Further evidence for cosmological evolution of the fine structure constant

We describe the results of a search for time variability of the fine structure constant alpha using absorption systems in the spectra of distant quasars. Three large optical data sets and two 21 cm and mm absorption systems provide four independent samples, spanning approximately 23% to 87% of the age of the universe. Each sample yields a smaller alpha in the past and the optical sample shows a 4 sigma deviation: Delta alpha/alpha = -0.72+/-0.18 x 10(-5) over the redshift range 0.5<z<3.5. We find no systematic effects which can explain our results. The only potentially significant systematic effects push Delta alpha/alpha towards positive values; i.e., our results would become more significant were we to correct for them.