Towards an accurate determination of the age of the Universe

In the past 40 years a considerable effort has been focused in determining the age of the Universe at zero redshift using several stellar clocks. In this review I will describe the best theoretical methods to determine the age of the oldest Galactic Globular Clusters (GC). I will also argue that a more accurate age determination may come from passively evolving high-redshift ellipticals. In particular, I will review two new methods to determine the age of GC. These two methods are more accurate than the classical isochrone fitting technique. The first method is based on the morphology of the horizontal branch and is independent of the distance modulus of the globular cluster. The second method uses a careful binning of the stellar luminosity function which determines simultaneously the distance and age of the GC. It is found that the oldest GCs have an age of $13.5 \pm 2$ Gyr. The absolute minimum age for the oldest GCs is 10.5 Gyr and the maximum is 16.0 Gyr (with 99% confidence). Therefore, an Einstein-De Sitter Universe ($\Omega=1$) is not totally ruled out if the Hubble constant is about $65 \pm 10$ km s$^{-1}$ Mpc$^{-1}$. On the other hand, the newly discovered red elliptical 53W069 ($z=1.43$) provides an stronger constraint since its minimun age is 3.2 Gyr, thus ruling out an Einstein-De Sitter Universe unless the Hubble constant is $\leq 45 \pm 10$ km s$^{-1}$. Using 53W069 we find an age at $z=0$ of $13 \pm 2$ Gyr, in excellent agreement with the GC determination.Comment: Invited review talk at the "DARK98, Heidelberg, mpi" meeting. To appear in IOP proc. series. LaTeX error fixe

Setting the stellar evolution clock for intermediate age populations

In this invited talk I show how the reddest and rarest galaxies at high redshift ($z \simeq 1.5$) can be used to set the stellar evolution clock. I argue that one can confidently compute the collapse redshift of these objects. This yields to a high collapse redshift ($z>6$) and therefore their age is well constrained (in all cosmologies) between 3 and 4 Gyr. I also show that this is, indeed, the age derived using a variety of synthetic stellar population models when proper statistical tools are used to analyse their observed spectral energy distribution. This allows me to conclude that all stellar population models yield to the same consistent age for these galaxies, i.e. about 3.5 Gyr and that the stellar clock is properly set. Low ages are therefore excluded with high confidence.Comment: Invited talk at the meeting "Spectrophotometric dating of stars and galaxies", Annapolis, USA, May 199

The role of star formation in the Tully-Fisher law

We investigate the influence of the star formation rate on the Tully-Fisher relation. We find that a simple model which combines the empirically-determined star-formation rate with the expected properties of galaxy halos provides a remarkably good fit to the absolute magnitude-rotation speed correlation. We find that the power-law nature, its slope, normalisation and scatter, are all readily accounted for if the Universe has a low density parameter, with or without a cosmological constant and disks are assembled at $z \sim 1 - 1.5$. Moreover, this agreement is found simultaneously in 4 wavebands. An Einstein-de Sitter Universe produces disks which are too faint unless the disks are assembled at $z\sim 0.5$. The scatter in the relation is due to a combination of the expected range of spin parameters of the halos and the range of formation redshifts. The source of the scatter opens up possibilities of a better galaxy distance indicator, if spectroscopic observations of globular clusters can be used to determine the halo rotation.Comment: MNRAS in pres

Disentangling the ICL with the CHEFs: Abell 2744 as a case study

Measurements of the intracluster light (ICL) are still prone to methodological ambiguities and there are multiple techniques in the literature for that purpose, mostly based on the binding energy, the local density distribution, or the surface brightness. A common issue with these methods is the a priori assumption of a number of hypotheses on either the ICL morphology, its surface brightness level or some properties of the brightest cluster galaxy (BCG). The discrepancy on the results is high, and numerical simulations just bound the ICL fraction in present-day galaxy clusters to the range 10-50%. We developed a new algorithm based on the Chebyshev-Fourier functions (CHEFs) to estimate the ICL fraction without relying on any a priori assumption on the physical or geometrical characteristics of the ICL. We are able to not only disentangle the ICL from the galatic luminosity but mark out the limits of the BCG from the ICL in a natural way. We test our tecnique with the recently released data of the cluster Abell 2744, observed by the Frontier Fields program. The complexity of this multiple merging cluster system and the formidable depth of these images make it a challenging test case to prove the efficiency of our algorithm. We found a final ICL fraction of 19.17+-2.87%, which is very consistent with numerical simulations.Comment: 19 pages, 12 figures, accepted for publication in the Astrophysical Journa

Geometry of central extensions of nilpotent Lie algebras

We obtain a recurrent and monotone method for constructing and classifying nilpotent Lie algebras by means of successive central extensions. It consists in calculating the second cohomology of an extendable nilpotent Lie algebra with the subsequent study of the orbit space geometry of the automorphism group action on Grassmannians defined in terms of the second cohomology of the extendable nilpotent Lie algebra. Such a geometric method allows to classify some classes of nilpotent Lie algebras. The concept of a rigid central extension is introduced.Comment: 2 figure

Light Higgs Boson Production in Two Higgs Doublets Models type III

By using the Cheng, Sher and Yuan's anzats, we study the light Higgs Boson production associated with $b$ quark production at TEVATRON using the 2HDM type III. We compare the simulations with experimental results coming from TEVATRON, finding valid ranges for the $bb$ coupling. By using these results, we calculate the cross section for the process $pp \to b\bar bh(b\bar b)$ for the LHC collider.Comment: $ pages, 4 figures, to appear Brazilian Journal of Physic

Differences of the Solar Magnetic Activity Signature in Velocity and Intensity Helioseismic Observations

The high-quality, full-disk helioseismic observations continuously collected by the spectrophotometer GOLF and the three photometers VIRGO/SPMs onboard the SoHO spacecraft for 17 years now (since April 11, 1996, apart from the SoHO "vacations") are absolutely unique for the study of the interior of the Sun and its variability with magnetic activity. Here, we look at the differences in the low-degree oscillation p-mode frequencies between radial velocity and intensity measurements taking into account all the known features of the p-mode profiles (e.g., the opposite peak asymmetry), and of the power spectrum (e.g., the presence of the higher degrees l= 4 and 5 in the signal). We show that the intensity frequencies are higher than the velocity frequencies during the solar cycle with a clear temporal dependence. The response between the individual angular degrees is also different. Time delays are observed between the temporal variations in GOLF and VIRGO frequencies. Such analysis is important in order to put new constraints and to better understand the mechanisms responsible for the temporal variations of the oscillation frequencies with the solar magnetic activity as well as their height dependences in the solar atmosphere. It is also important for the study of the stellar magnetic activity using asteroseismic data.Comment: 6 pages, 2 figures. To be published in the Conference Series of Astronomical Society of the Pacific, NSO Workshop #27 "Fifty Years of Seismology of the Sun and Stars", May 2013, Tucson, A

Surgery spectral sequence and stratified manifolds

Cappell and Shaneson pointed out in 1978 interesting properties of Browder - Livesay invariants which are similar to differentials in some spectral sequence. Such spectral sequence was constructed in 1991 by Hambleton and Kharshiladze. This spectral sequence is closely related to a problem of realization of elements of Wall groups by normal maps of closed manifolds. The main step of construction of the spectral sequence is an infinite filtration of spectra in which only the first two, as is well-known, have clear geometric sense. The first one is a spectrum $\Bbb L(\pi_1(X))$ for surgery obstruction groups of a manifold $X$ and the second $\Bbb LP_*(F)$ is a spectrum for surgery on a Browder-Livesay manifold pair $Y\subset X$. The geometric sense of the third term of filtration was explained by Muranov, Repov\v{s}, and Spaggiari in 2002. In the present paper we give a geometric interpretation of all spectra of filtration in construction of Hambleton and Kharshiladze. We introduce groups of obstructions to surgery on a system of embeddedd manifolds and prove that spectra which realize these groups coincide with spectra in the filtration of Hambleton and Kharshiladze. We describe algebraic and geometric properties of introduced obstruction groups and their relations to the classical surgery theory. We prove isomorphism between introduced groups and Browder-Quinn $L$-groups of stratified manifolds. We give an application of our results to closed manifold surgery problem and iterated Browder-Livesay invariant.Comment: Trans. Moscow Math. Soc., to appea

Supersymmetric Electroweak Renormaliztion of the Z-Width in the MSSM (II)

We address the computation of \Gamma_Z and of the intriguing quantity R_b in the MSSM including full treatment of the Higgs sector. For a pseudoscalar Higgs mass m_{A^0}>70\,GeV and CDF limits on m_t, the bounds on R_b at 1\sigma level leave no room to the MSSM to solve the `R_b crisis' for any combination of the parameters, not even admitting the possibility of a light chargino and a light stop of O(50) GeV; however, for m_t not restricted by CDF, a `tangential' solution exists in the window 2<\tan\beta<10 with a light chargino and stop. In contrast, for a pseudoscalar mass 40\,GeV<m_{A^0}<60\,GeV and CDF limits on m_t, the `R_b crisis' can be solved in a comfortable way, for any SUSY spectrum above the phenomenological bounds, provided \tan\beta>m_t/m_b. Our general conclusion is that, if there is a `R_b crisis' at all, its solution within the MSSM has to do more with the peculiar structure of the SUSY Higgs sector rather than with the spectrum of genuine supersymmetric particles. In view of the range predicted for m_{A^0}, LEP 200 should be able to definitely settle down this question.Comment: 16 p. in LaTeX. Preprint UAB-FT-344. Error in the labelling of fig.3 corrected. Results unchange

Growth mechanisms and structure of fullerene-like carbon-based thin films: superelastic materials for tribological applications

In this chapter we review our findings on the bonding structure and growth mechanisms of carbon-based thin solid films with fullerene-like (FL) microstructure. The so-called FL arrangements arise from the curvature and cross-linking of basal planes in graphitic-like structures, partially resembling that of molecular fullerenes. This three-dimensional superstructure takes advantage of the strength of planar pi bonds in sp2 hybrids and confers the material interesting mechanical properties, such as high hardness, high elastic recovery, low-friction and wear-resistance. These properties can be tailored by controlling the curvature, size and connectivity of the FL arrangements, making these materials promising coatings for tribological applications. We have focused our interest mostly on carbon nitride (CNx) since nitrogen promotes the formation of FL arrangements at low substrate temperatures and they are emerging over pure carbon coatings in tribological applications such as protective overcoats in magnetic hard disks. We address structural issues such as origin of plane curvature, nature of the cross-linking sites and sp2 clustering, together with growth mechanisms based on the role of film-forming precursors, chemical re-sputtering or concurrent ion assistance during growth.Comment: Review article in "Fullerene Research Trends" to be published by Nova Science Publishers Inc., New York. 46 page