arXiv subjects

C. J. A. P. Martins

Publications and source records attributed to C. J. A. P. Martins.

At least 217 records · Page 12Linked to original sources

arXiv2013

The UVES Large Program for Testing Fundamental Physics II: Constraints on a Change in μ Towards Quasar HE 0027-1836

We present an accurate analysis of the H2 absorption lines from the zabs ~ 2.4018 damped Lyα system towards HE 0027-1836 observed with the Very Large Telescope Ultraviolet and Visual Echelle Spectrograph (VLT/UVES) as a part of the European Southern Observatory Large Programme "The UVES large programme for testing fundamental physics" to constrain the variation of proton-to-electron mass ratio, μ = mp/me. We perform cross-correlation analysis between 19 individual exposures taken over three years and the combined spectrum to check the wavelength calibration stability. We notice the presence of a possible wavelength dependent velocity drift especially in the data taken in 2012. We use available asteroids spectra taken with UVES close to our observations to confirm and quantify this effect. We consider single and two component Voigt profiles to model the observed H2 absorption profiles. We use both linear regression analysis and Voigt profile fitting where Δμ/μ is explicitly considered as an additional fitting parameter. The two component model is marginally favored by the statistical indicators and we get Δμ/μ = (-2.5 +/- 8.1(stat) +/- 6.2(sys)) ppm. When we apply the correction to the wavelength dependent velocity drift we find Δμ/μ = (-7.6 +/- 8.1(stat) +/- 6.3(sys)) ppm. It will be important to check the extent to which the velocity drift we notice in this study is present in UVES data used for previous Δμ/μ measurements.

astro-ph.CO↗

arXiv2013

A test of unification towards the radio source PKS1413+135

We point out that existing astrophysical measurements of combinations of the fine-structure constant $α$, the proton-to-electron mass ratio $μ$ and the proton gyromagnetic ratio $g_p$ towards the radio source PKS1413+135 can be used to individually constrain each of these fundamental couplings. While the accuracy of the available measurements is not yet sufficient to test the spatial dipole scenario, our analysis serves as a proof of concept as new observational facilities will soon allow significantly more robust tests. Moreover, these measurements can also be used to obtain constraints on certain classes of unification scenarios, and we compare the constraints obtained for PKS1413+135 with those previously obtained from local atomic clock measurements.

astro-ph.CO↗

arXiv2013

The UVES Large Program for Testing Fundamental Physics: I Bounds on a change in alpha towards quasar HE 2217-2818

Absorption line systems detected in quasar spectra can be used to compare the value of the fine-structure constant, α, measured today on Earth with its value in distant galaxies. In recent years, some evidence has emerged of small temporal and also spatial variations of α on cosmological scales which may reach a fractional level of ~ 10 ppm (parts per million). To test these claims we are conducting a Large Program with the VLT UVES . We are obtaining high-resolution (R ~ 60000 and high signal-to-noise ratio (S/N ~ 100) UVES spectra calibrated specifically for this purpose. Here we analyse the first complete quasar spectrum from this Program, that of HE 2217-2818. We apply the Many Multiplet method to measure α in 5 absorption systems towards this quasar: zabs = 0.7866, 0.9424, 1.5558, 1.6279 and 1.6919. The most precise result is obtained for the absorber at zabs = 1.6919 where 3 Fe II transitions and Al II λ1670 have high S/N and provide a wide range of sensitivities to α. The absorption profile is complex, with several very narrow features, and requires 32 velocity components to be fitted to the data. Our final result for the relative variation in α in this system is Deltaα/α = +1.3 +/- 2.4stat +/- 1.0sys ppm. This is one of the tightest current bounds on α variation from an individual absorber. The absorbers towards quasar HE 2217-2818 reveal no evidence for variation in α at the 3 ppm precision level (1σ confidence). If the recently reported 10 ppm dipolar variation of α across the sky were correct, the expectation at this sky position is (3.2-5.4) +/-1.7 ppm depending on dipole model used . Our constraint of Deltaα/α=+1.3+/-2.4stat +/-1.0sys ppm is not inconsistent with this expectation.

astro-ph.CO↗

arXiv2012

Three Tests of LambdaCDM

The observational evidence for the acceleration of the universe demonstrates that canonical theories of gravitation and particle physics are incomplete, if not incorrect. A new generation of astronomical facilities will shortly be able to carry out precision consistency tests of the standard cosmological model and search for evidence of new physics beyond it. I describe some of these tests, focusing on the universality of nature's fundamental couplings and the characterization of the properties of dark energy. I will also comment on prospects for forthcoming ESA and ESO facilities in which the CAUP Dark Side team is involved.

astro-ph.CO↗

arXiv2012

Probing unification scenarios with atomic clocks

We discuss the usage of measurements of the stability of nature's fundamental constants coming from comparisons between atomic clocks as a means to constrain coupled variations of these constants in a broad class of unification scenarios. After introducing the phenomenology of these models we provide updated constraints, based on a global analysis of the latest experimental results. We obtain null results for the proton-to-electron mass ratio ${\dotμ}/μ=(0.68\pm5.79)\ti mes10^{-16}\, {\rm yr}{}^{-1}$ and for the gyromagnetic factor ${\dot g_p}/{g_p} =(-0.72\pm0.89)\times10^{-16}\, {\rm yr}{}^{-1}$ (both of these being at the 95 % confidence level). These results are compatible with theoretical expectations on unification scenarios, but much freedom exists due to the presence of a degeneracy direction in the relevant parameter space.

hep-ph↗

arXiv2012

Accurate Calibration of the Velocity-dependent One-scale Model for Domain Walls

We study the asymptotic scaling properties of standard domain wall networks in several cosmological epochs. We carry out the largest field theory simulations achieved to date, with simulation boxes of size 20483, and confirm that a scale-invariant evolution of the network is indeed the attractor solution. The simulations are also used to obtain an accurate calibration for the velocity-dependent one-scale model for domain walls: we numerically determine the two free model parameters to have the values $c_w = 0.34\pm0.16$ and $k_w = 0.98\pm0.07$, which are higher precision than (but in agreement with) earlier estimates.

hep-ph↗

arXiv2012

Probing dark energy with redshift-drift

Future redshift-drift measurements (also known as Sandage-Loeb signal) will be crucial to probe the so called "redshift desert", thus providing a new tool for cosmological studies. In this paper we quantify the ability of a future measurement of the Sandage-Loeb signal by a CODEX-like spectrograph to constrain a phenomenological parametrization of dynamical dark energy, specifically by obtaining constraints on $w_0$ and $w_a$. We also demonstrate that if used alongside CMB data, the Sandage-Loeb measurements will be able to break degeneracies between expansion parameters, thus greatly improving cosmological constraints.

astro-ph.CO↗

arXiv2012

Constraints of the variation of fundamental couplings and sensitivity of the equation of state of dense matter

We discuss the coupled variations of the gravitational, strong and electroweak coupling constants and the current knowledge of the nuclear equation of state based on heavy ion collision experiments and neutron star mass-radius relationship. In particular we focus in our description on phenomenological parameters, $R$, relating variations in the quantum chromodynamics scale $Λ_{QCD}$ and the fine structure constant $α$, and $S$, relating variation of $v$, the Higgs vacuum expectation value and the Yukawa couplings, $h$, in the quark sector. This parametrization is valid for any model where gauge coupling unification occurs at some (unspecified) high energy scale. From a physically motivated set of equations of state for dense matter we obtain the constrained parameter phase space $(R, S)$ in high density nuclear environments. This procedure is complementary to (although currently less powerful than) those used in low density conditions. For variations of $Δα/α=0.005$ we find that the obtained constrained parameter lies on a strip region in the $(R, S)$ plane that partially overlaps some of the allowed values of parameters derived from primordial abundances. This may be of interest in the context of unification scenarios where a dense phase of the universe may have existed at early times.

astro-ph.CO↗

arXiv2012

Constraining cosmologies with fundamental constants I. Quintessence and K-Essence

Many cosmological models invoke rolling scalar fields to account for the observed acceleration of the expansion of the universe. These theories generally include a potential V(phi) which is a function of the scalar field phi. Although V(phi) can be represented by a very diverse set of functions, recent work has shown the under some conditions, such as the slow roll conditions, the equation of state parameter w is either independent of the form of V(phi) or is part of family of solutions with only a few parameters. In realistic models of this type the scalar field couples to other sectors of the model leading to possibly observable changes in the fundamental constants such as the fine structure constant alpha and the proton to electron mass ratio mu. This paper explores the limits this puts on the validity of various cosmologies that invoke rolling scalar fields. We find that the limit on the variation of mu puts significant constraints on the product of a cosmological parameter w+1 times a new physics parameter zeta_mu^2, the coupling constant between mu and the rolling scalar field. Even when the cosmologies are restricted to very slow roll conditions either the value of zeta_mu must be at the lower end of or less than its expected values or the value of w+1 must be restricted to values vanishingly close to 0. This implies that either the rolling scalar field is very weakly coupled with the electromagnetic field, small zeta_mu, very weakly coupled with gravity, w+1 ~ 0 or both. These results stress that adherence to the measured invariance in mu is a very significant test of the validity of any proposed cosmology and any new physics it requires. The limits on the variation of mu also produces a significant tension with the reported changes in the value of alpha.

astro-ph.CO↗

arXiv2012

Variation of fundamental parameters and dark energy. A principal component approach

We discuss methods based on Principal Component Analysis to constrain the dark energy equation of state using a combination of Type Ia supernovae at low redshift and spectroscopic measurements of varying fundamental couplings at higher redshifts. We discuss the performance of this method when future better-quality datasets are available, focusing on two forthcoming ESO spectrographs - ESPRESSO for the VLT and CODEX for the E-ELT - which include these measurements as a key part of their science cases. These can realize the prospect of a detailed characterization of dark energy properties almost all the way up to redshift 4.

astro-ph.CO↗

arXiv2012

A stellar test of the physics of unification

We discuss the feasibility of using solar-type main-sequence stars as probes of fundamental physics and unification. We use a simple polytropic stellar structure model and study its sensitivity to variations of the gravitational, strong and electroweak coupling constants in the context of unification scenarios. We quantify the sensitivity of the Sun's interior temperature to these variations, finding $|Δα/α|\lesssim1.3\times10^{-4}$ for a 'canonical' choice of unification scenario, and discuss prospects for future improvements.

astro-ph.SR↗

arXiv2012

Three tests of LambdaCDM

The observational evidence for the acceleration of the universe demonstrates that canonical theories of gravitation and particle physics are incomplete, if not incorrect. The next generation of astronomical facilities must both be able to carry out precision consistency tests of the standard cosmological model and search for evidence of new physics beyond it. I describe some of these tests, and discuss prospects for facilities in which the CAUP Dark Side team is involved, specifically ESPRESSO, Euclid and CODEX.

astro-ph.CO↗

arXiv2012

Probing dark energy beyond $z=2$ with CODEX

Precision measurements of nature's fundamental couplings and a first measurement of the cosmological redshift drift are two of the key targets for future high-resolution ultra-stable spectrographs such as CODEX. Being able to do both gives CODEX a unique advantage, allowing it to probe dynamical dark energy models (by measuring the behavior of their equation of state) deep in the matter era and thereby testing classes of models that would otherwise be difficult to distinguish from the standard $Λ$CDM paradigm. We illustrate this point with two simple case studies.

astro-ph.CO↗

arXiv2012

The Fine Structure Constant and the CMB Damping Scale

The recent measurements of the Cosmic Microwave Background anisotropies at arcminute angular scales performed by the ACT and SPT experiments are probing the damping regime of CMB fluctuations. The analysis of these datasets unexpectedly suggests that the effective number of relativistic degrees of freedom is larger than the standard value of Neff = 3.04, and inconsistent with it at more than two standard deviations. In this paper we study the role of a mechanism that could affect the shape of the CMB angular fluctuations at those scales, namely a change in the recombination process through variations in the fine structure constant. We show that the new CMB data significantly improve the previous constraints on variations of α, with α/α0 = 0.984 \pm 0.005, i.e. hinting also to a more than two standard deviation from the current, local, value α0. A significant degeneracy is present between α and Neff, and when variations in the latter are allowed the constraints on α are relaxed and again consistent with the standard value. Deviations of either parameter from their standard values would imply the presence of new, currently unknown physics.

astro-ph.CO↗

arXiv2012

Cosmic string evolution with a conserved charge

Cosmic strings with degrees of freedom beyond the standard Abrikosov-Nielsen-Olesen or Nambu-Goto strings are ubiquitous in field theory as well as in models with extra dimensions, such as string theoretic brane inflation scenarios. Here we carry out an analytic study of a simplified version of one such cosmic string model. Specifically, we extend the velocity-dependent one-scale (VOS) string evolution model to the case where there is a conserved microscopic charge on the string worldsheet. We find that whether the standard scale-invariant evolution of the network is preserved or destroyed due to the presence of the charge will crucially depend on the amount of damping and energy losses experienced by the network. This suggests, among other things, that results derived in Minkowski space (field theory) simulations may not extend to the case of an expanding universe.

hep-ph↗

arXiv2011

Constraints on the CMB temperature redshift dependence from SZ and distance measurements

The relation between redshift and the CMB temperature, $T_{CMB}(z)=T_0(1+z)$ is a key prediction of standard cosmology, but is violated in many non-standard models. Constraining possible deviations to this law is an effective way to test the $Λ$CDM paradigm and search for hints of new physics. We present state-of-the-art constraints, using both direct and indirect measurements. In particular, we point out that in models where photons can be created or destroyed, not only does the temperature-redshift relation change, but so does the distance duality relation, and these departures from the standard behaviour are related, providing us with an opportunity to improve constraints. We show that current datasets limit possible deviations of the form $T_{CMB}(z)=T_0(1+z)^{1-β}$ to be $β=0.004\pm0.016$ up to a redshift $z\sim 3$. We also discuss how, with the next generation of space and ground-based experiments, these constraints can be improved by more than one order of magnitude.

astro-ph.CO↗

arXiv2011

Scaling Properties of Domain Wall Networks

We revisit the cosmological evolution of domain wall networks, taking advantage of recent improvements in computing power. We carry out high-resolution field theory simulations in two, three and four spatial dimensions to study the effects of dimensionality and damping on the evolution of the network. Our results are consistent with the expected scale-invariant evolution of the network, which suggests that previous hints of deviations from this behavior may have been due to the limited dynamical range of those simulations. We also use the results of very large ($1024^3$) simulations in three cosmological epochs to provide a calibration for the velocity-dependent one-scale model for domain walls: we numerically determine the two free model parameters to have the values $c_w=0.5\pm0.2$ and $k_w=1.1\pm0.3$.

hep-ph↗

arXiv2011

Analytic Models for the Evolution of Semilocal String Networks

We revisit previously developed analytic models for defect evolution and adapt them appropriately for the study of semilocal string networks. We thus confirm the expectation (based on numerical simulations) that linear scaling evolution is the attractor solution for a broad range of model parameters. We discuss in detail the evolution of individual semilocal segments, focusing on the phenomenology of segment growth, and also provide a preliminary comparison with existing numerical simulations.

hep-ph↗