Search

We study scalar field theories invariant under transverse diffeomorphisms in cosmological contexts. We show that in the geometric optics approximation, the corresponding particles move along geodesics and contribute with the same active mass (energy) to the gravitational field as in Diff invariant theories. However, for low-frequency modes, the contributions to the energy-momentum tensor differ from that of Diff invariant theories. This opens up a wide range of possibilities for cosmological model building. As an example, we show that the simplest TDiff invariant scalar field theory with only kinetic term could drive inflation and generate a red-tilted spectrum of density fluctuations. We also present a detailed analysis of cosmological perturbations and show that the breaking of full Diff invariance generically induces new non-adiabatic pressure perturbations. A simple scalar field dark matter model based on a purely kinetic term that exhibits the same clustering properties as standard cold dark matter is also presented., 15 pages

The Fisher gAlaxy suRvey cOde ($\texttt{FARO}$) is a new public Python code that computes the Fisher matrix for galaxy surveys observables. The observables considered are the linear multitracer 3D galaxy power spectrum, the linear convergence power spectrum for weak lensing, and the linear multitracer power spectrum for the correlation between galaxy distribution and convergence. The code allows for tomographic and model-independent analysis in which, for scale-independent growth, the following functions of redshift $A_a (z) \equiv \sigma_{8}(z) \, b_a (z)$, $R(z) \equiv \sigma_{8}(z) \, f(z)$, $L(z) \equiv \Omega_{m} \, \sigma_{8}(z) \, \Sigma (z)$ and $E(z) \equiv H(z)/H_0$, together with the function of scale $\hat{P}(k)$, are taken as free parameters in each redshift and scale bins respectively. In addition, a module for change of variables is provided to project the Fisher matrix on any particular set of parameters required. The code is built to be as fast as possible and user-friendly. As an application example, we forecast the sensitivity of future galaxy surveys like DESI, Euclid, J-PAS and LSST and compare their performance on different redshift and scale ranges., Comment: https://www.ucm.es/iparcos/faro

This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©2011 RAS © 2011 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved, The detection of extremely massive clusters at z > 1 such as SPT-CLJ0546-5345, SPT-CLJ2106-5844 and XMMUJ2235.3-2557 has been considered by some authors as a challenge to the standard Λ cold dark matter cosmology. In fact, assuming Gaussian initial conditions, the theoretical expectation of detecting such objects is as low as ≤1 per cent. In this paper we discuss the probability of the existence of such objects in the light of the vector dark energy paradigm, showing by means of a series of N-body simulations that chances of detection are substantially enhanced in this non-standard framework, EC is supported by the MareNostrum project funded by the Spanish Ministerio de Ciencia e Innovación (MICINN) under grant no. AYA2009-13875-C03-02 and MultiDark Consolider project under grant CSD2009-00064. AK acknowledges support by the MICINN’s Ramón y Cajal programme as well as the grants AYA 2009-13875-C03-02, AYA2009-12792- C03-03, CSD2009- 00064, and CAM S2009/ESP-1496. GY acknowledges support from MICINN’s grants AYA2009- 13875-C03-02 and FPA2009- 08958. JBJ is supported by the Ministerio de Educación under the post-doctoral contract EX2009-0305 and also wishes to acknowledge support from the Norwegian Research Council under the YGGDRASIL programme 2009-2010 and the NILS mobility project grant UCM-EEA-ABEL-03-2010. We also acknowledge support from MICINN (Spain) project numbers FIS 2008-01323, FPA 2008-00592 and CAM/UCM 910309

The Higgs mechanism predicts, apart from the existence of a new scalar boson, the presence of a constant Higgs field that permeates all of space. The vacuum expectation value (VEV) of this field is affected by quantum corrections which are mainly generated by the self-interactions and couplings of the Higgs field to gauge bosons and heavy quarks. In this work we show that gravity can affect, in a non-trivial way, these quantum corrections through the finite parts of the one-loop contributions to the effective potential. In particular, we consider the corrections generated by the Standard Model Higgs self-interactions in slowly-varying weak gravitational backgrounds. The obtained results amount to the existence of non-negligible inhomogeneities in the Higgs VEV. Such inhomogeneities translate into spatial variations of the particle masses, and in particular of the proton-to-electron mass ratio. We find that these Higgs perturbations in our Solar System are controlled by the Eddington parameter, and are absent in pure General Relativity. Yet, they may be present in modified gravity theories. This predicted effect may be constrained by atomic clocks or high-resolution spectroscopic measurements, which could allow to improve current limits on modifications of Einstein's gravity., Comment: This paper has been withdrawn by the authors due to an error detected in the inhomogeneous contribution to the effective potential

Cembranos, J.A.R. "Solution to the Isotropy Problem for Cosmological Hidden Vector Models" in Proceedings, 9th Patras Workshop on Axions, WIMPs and WISPs (AXION-WIMP 2013) / Oberlack, Uwe, Sissol, Pierre (eds.), 2013 ; AXION-WIMP 2013 : 9th Patras Workshop on Axions, WIMPs and WISPs , 2013-06-23 - 2013-06-28, Mainz 9th Patras Workshop on Axions, WIMPs and WISPs, AXION-WIMP 2013, Mainz, Germany, 24 Jun 2013 - 28 Jun 2013; Hamburg : Verlag Deutsches Elektronen-Synchrotron, DESY-PROC 231-234 (2013). doi:10.3204/DESY-PROC-2013-04/cembranos_jose, Gauge bosons associated to new gauge symmetries under which the standard model particles are not charged are predicted in many extensions of the standard model of particles and interactions. We show that under very general conditions, the average energy-momentum tensor of these rapidly oscillating vector fields is isotropic for any locally inertial observer. This result has a fundamental importance in order to consider coherent vector fields as a viable alternative to support models of dark matter, dark energy or inflation., Published by Verlag Deutsches Elektronen-Synchrotron, Hamburg

This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2012 RAS ©: 2012 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved., We present the results of a series of cosmological N-body simulations of a vector dark energy (VDE) model, performed using a suitably modified version of the publicly available gadget-2 code. The set-ups of our simulations were calibrated pursuing a twofold aim: (1) to analyse the large-scale distribution of massive objects and (2) to determine the properties of halo structure in this different framework. We observe that structure formation is enhanced in VDE, since the mass function at high redshift is boosted up to a factor of 10 with respect to Λ cold dark matter (ΛCDM), possibly alleviating tensions with the observations of massive clusters at high redshifts and early reionization epoch. Significant differences can also be found for the value of the growth factor, which in VDE shows a completely different behaviour, and in the distribution of voids, which in this cosmology are on average smaller and less abundant. We further studied the structure of dark matter haloes more massive than 5 × 10 13h -1M ⊙, finding that no substantial difference emerges when comparing spin parameter, shape, triaxiality and profiles of structures evolved under different cosmological pictures. Nevertheless, minor differences can be found in the concentration-mass relation and the two-point correlation function, both showing different amplitudes and steeper slopes. Using an additional series of simulations of a ΛCDM scenario with the same and σ 8 used in the VDE cosmology, we have been able to establish whether the modifications induced in the new cosmological picture were due to the particular nature of the dynamical dark energy or a straightforward consequence of the cosmological parameters. On large scales, the dynamical effects of the cosmic vector field can be seen in the peculiar evolution of the cluster number density function with redshift, in the shape of the mass function, in the distribution of voids and on the characteristic form of the growth index γ(z). On smaller scales, internal properties of haloes are almost unaffected by the change of cosmology, since no statistical difference can be observed in the characteristics of halo profiles, spin parameters, shapes and triaxialities. Only halo masses and concentrations show a substantial increase, which can, however, be attributed to the change in the cosmological parameters, EC is supported by the MareNostrum project funded by the Spanish Ministerio de Ciencia e Innovación (MICINN) under grant no. AYA2009-13875-C03-02 and MultiDark Consolider project under grant CSD2009-00064. Acknowledges support by the MICINN’s Ramón y Cajal programme as well as the grants AYA2009-13875-C03-02,AYA2009-12792-C03- 03, CSD2009-00064 and CAM S2009/ESP-1496. GY would like to thank the MICINN for financial support under grants AYA 2009- 13875-C03 and FPA 2009-08958, and the SyeC Consolider project CSD2007-00050. JBJ is supported by the Ministerio de Educación under the postdoctoral contract EX2009-0305 and also wishes to acknowledge support from the Norwegian Research Council under the YGGDRASIL programme 2009–2010 and the NILS mobility project grant UCM-EEA-ABEL-03-2010. We also acknowledge support from MICINN (Spain) project numbers FIS 2008-01323, FPA 2008-00592, CAM/UCM 910309 and FIS2011-23000

In this work we consider quantum electromagnetic fields in an expanding universe. We start by reviewing the difficulties found when trying to impose the Lorenz condition in a time-dependent geometry. Motivated by this fact, we explore the possibility of extending the electromagnetic theory by allowing the scalar state which is usually eliminated by means of the Lorenz condition to propagate, preserving at the same time the dynamics of ordinary transverse photons. We show that the new state cannot be generated by charged currents, but it breaks conformal invariance and can be excited gravitationally. In fact, primordial quantum fluctuations produced during inflation can give rise to super-Hubble temporal electromagnetic modes whose energy density behaves as a cosmological constant. The value of the effective cosmological constant is shown to agree with observations provided inflation took place at the electroweak scale. The theory is compatible with all the local gravity tests and is free from classical or quantum instabilities. Thus we see that, not only the true nature of dark energy can be established without resorting to new physics, but also the value of the cosmological constant finds a natural explanation in the context of standard inflationary cosmology. On sub-Hubble scales, the new state generates an effective charge density which, due to the high electric conductivity of the cosmic plasma after inflation, gives rise to both vorticity and magnetic fields. Present upper limits on vorticity coming from CMB anisotropies are translated into lower limits on the present value of cosmic magnetic fields. We find that magnetic fields $B_{\lambda}> 10^{-12}$ G can be typically generated with coherence lengths ranging from sub-galactic scales up to the present Hubble radius., Comment: 9 pages, 2 figures. Talk given at the Yukawa Institute for Theoretical Physics Symposium YKIS2010, "Cosmology-the Next Generation", Kyoto, 28 June-2 July, 2010. To appear in Progress of Theoretical Physics Supplement

A modified f(R) gravity model has been recently proposed in Phys. Rev. Lett. 102, 221101 (2009) [arXiv:0905.1941] whose cosmological behaviour is clearly distinguishable from LCDM. Contrary to previous opinions which consider that self-consistent f(R) gravity models distinct from LCDM are almost ruled out, the authors claim that the proposed model is cosmologically viable. Here we show that although the model satisfies some consistency conditions, precisely because of its departure from LCDM behaviour, it does not satisfy local gravity constraints and, in addition, the predicted matter power spectrum conflicts with SDSS data., 1 page, 1 figure. Accepted for publication in Physical Review Letters

It has been recently shown that the presence of a vector field over cosmological scales could explain the observed accelerated expansion of the universe without introducing neither new scales nor unnatural initial conditions in the early universe, thus avoiding the coincidence problem. Here, we present a detailed analysis of the constraints imposed by SNIa, CMB and BAO data on the vector dark energy model with general spatial curvature. We find that contrary to standard cosmology, CMB data excludes a flat universe for this model and, in fact, predicts a closed geometry for the spatial sections. We see that CMB and SNIa Gold data are perfectly compatible at the 1-sigma level, however SNIa Union dataset exhibits a 3-sigma tension with CMB. The same level of tension is also found between SNIa and BAO measurements., Comment: 7 pages, 3 figures. New figure and references included. Final version to appear in Phys. Rev. D

In the context of $f(R)$ theories of gravity, we study the evolution of scalar cosmological perturbations in the metric formalism. Using a completely general procedure, we find the exact fourth-order differential equation for the matter density perturbations in the longitudinal gauge. In the case of sub-Hubble modes, the expression reduces to a second-order equation which is compared with the standard (quasi-static) equation used in the literature. We show that for general $f(R)$ functions the quasi-static approximation is not justified. However, for those functions adequately describing the present phase of accelerated expansion and satisfying local gravity tests, it provides a correct description for the evolution of perturbations., 9 pages, 4 figures. New comments and references included. Final version to appear in Phys.Rev. D

We explore the possibility that the present stage of accelerated expansion of the universe is due to the presence of a cosmic vector field. We show that vector theories allow for the generation of an accelerated phase without the introduction of potential terms or unnatural scales in the Lagrangian. We propose a particular model with the same number of parameters as LCDM and excellent fits to SNIa data. The model is scaling during radiation era, with natural initial conditions, thus avoiding the cosmic coincidence problem. Upcoming observations will be able to clearly discriminate it from standard LCDM cosmology, Comment: 4 pages, 2 figures. Contribution to the proceedings of 43rd Rencontres de Moriond: Cosmology, La Thuile, Italy, 15-22 Mar 2008

Brane world theories contain additional degrees of freedom related to the geometry of the extra dimension space which can be understood as brane oscillations (branons). In the case where the fundamental gravitational scale is much larger than the brane tension scale, these branons are the only extra degrees of freedom at low energies coming from the extra dimensions. Branons are generically stable, weakly interacting and massive. They could be produced in the next generation colliders and at the same time they are natural WIMP like candidates for dark matter., 4 pages, 3 figures. Final version to appear in Proceedings of the Vth Rencontres du Vietnam, Hanoi, August 5-11 2004

With the beginning of the XXIst century, a physical model of our Universe, usually called the Standard Cosmological Model (SCM), is reaching an important level of consolidation, based on accurate astrophysical data and also on theoretical developments. In this paper we review the interplay between the basic concepts and observations underlying this model. The SCM is a complex and beautiful building, recieving inputs from many branches of physics. Major topics reviewed are: General Relativity and the cosmological constant, the Cosmological Principle and Friedmann-Robertson-Walker-Lemaitre models, Hubble diagrams and dark energy, large scale structure and dark matter, the cosmic microwave background, Big Bang nucleosynthesis, and inflation., Comment: 26 pages, 3 figures. To appear on the volume dedicated to Prof. Alberto Galindo Tixaire on occasion of his 70th birthday

We briefly review the distinctive signals of brane world models with low tension. We pay special attention to the brane fluctuations (branons), whose phenomenological consequences could be important both in high energy particle physics experiments and in astrophysical and cosmological observations., Comment: 4 pages, 1 figure. Proceedings of the 29th Spanish Physical Royal Society Biennial on the centennial of the society, Madrid, Spain, July 2003

We consider the amplification of electromagnetic quantum vacuum fluctuations induced by the presence of metric perturbations at the end of inflation. We obtain the amplitude of the corresponding magnetic fields on super-Hubble scales and compare it with the requirements of the galactic dynamo mechanism for different values of the spectral index. Finally we discuss the possible effects of the dissipation of such fields in the form of gravitational waves., Comment: 8 pages, 1 figure. Presented at COSMO-01 conference, Rovaniemi, Finland, August 29-September 4, 2001

We present a new technique for the calculation of helicity $\pm 1/2$ gravitino production during preheating. It is based on the equivalence between goldstinos and helicity $\pm 1/2$ gravitinos at high energies. The problem is thus reduced to the standard (Majorana) fermion production after inflation. Comparison with the results obtained in the unitary gauge is also presented., Comment: 4 pages, LaTeX, uses moriond.sty. Talk given at XXXVth Recontres de Moriond "Energy Densities in the Universe", Les Arcs, France, January 22-29, 2000

We study the effective action for gravity obtained after the integration of scalar matter fields, using the local momentum representation based on the Riemann normal coordinates expansion. By considering this expansion around different space-time points, we also compute the non-local terms together with the more usual divergent ones. We discuss the applicability of our results to the calculation of particle production rates in cosmological backgrounds and compare this method with the traditional Bogolyubov transformations., Comment: 8 pages, Latex. Contribution to the Proceedings of the International Seminar on Mathematical Cosmology, Potsdam (Germany), March 30 - April 4, 1998

Torsion appears in a natural way in modern formulations of the gravitational theories. In this work we study several aspects of the interplay between the Standard Model and a classical gravitational background with torsion. In particular we consider the problem of the gauge and gravitational anomalies, $B$ and $L$ anomalies, the effective action for the torsion and the propagation of electromagnetic radiation in the presence of torsion., Comment: 18 pages, LaTeX. To appear in "Contemporary Fundamental Physics", Ed. Valeri Dvoeglazov (Nova Science Publishers)

In the presence of a curved space-time with torsion, the divergence of the leptonic current gets new contributions from the curvature and the torsion in addition to those coming from the electroweak fields. However it is possible to define a new lepton current which is gauge and local Lorentz invariant whose divergence gets no contribution from the torsion. Therefore we argue that torsion does not contribute to anomalous lepton number production, 9 pages, LaTeX, revised version with a new interpretation of the results

It has been suggested that our universe could be a 3-dimensional brane where the SM fields live embedded in a D-dimensional space-time. In flexible raneworlds, in addition to the SM fields, new degrees of freedom appear on the brane associated to brane fluctuations. These new fields, known as branons, are standard WIMPs (Weakly Interacting Massive Particles) and therefore natural dark matter candidates, whose spontaneous annihilations can provide first evidences for this scenario., 7 pages, 1 figure. Contributed to XXIII International Symposium on Lepton and Photon Interactions at High Energy, Aug 13-18, Daegu, Korea

In extra-dimensional brane-world models with low tension, brane excitations provide a natural WIMP candidate for dark matter. Taking into account the various constraints coming from colliders, precision observables and direct search, we explore the possibilities for indirect search of the galactic halo branons through their photon producing annihilations in experiments such as EGRET, HESS or AMS2., 3 pages, no figures. Contribution to the Proceedings of Eleventh Marcel Grossmann Meeting on General Relativity, Berlin, July 23-29, 2006

In this work we compute the effective action describing the low-energy brane Goldstone-boson dynamics. The Goldstone bosons or branons appear because the brane spontaneously breaks the translational invariance along the extra dimensions. We discuss the Higgs-like mechanism in which the Kaluza-Klein gauge fields absorb the Goldstone bosons and acquire mass. We also present the explicit form of the effective action describing the low-energy interactions between the three-brane Goldstone bosons and the Standard Model fields. In addition to the branons, two new kinds of states arise corresponding to Skyrmion-like solutions and wrapped states. We study the main properties of these states, their geometrical interpretation and the relations between them., Comment: 22 pages, 4 figures. Contributed to 20th International Symposium on Lepton and Photon Interactions at High Energies (Lepton Photon 01), Rome, Italy, 23-28 July 2001

The Javalambre-Physics of the Accelerated Universe Astrophysical Survey (J-PAS) is a narrow band, very wide field Cosmological Survey to be carried out from the Javalambre Observatory in Spain with a purpose-built, dedicated 2.5m telescope and a 4.7 sq.deg. camera with 1.2Gpix. Starting in late 2015, J-PAS will observe 8500sq.deg. of Northern Sky and measure $0.003(1+z)$ photo-z for $9\times10^7$ LRG and ELG galaxies plus several million QSOs, sampling an effective volume of $\sim 14$ Gpc$^3$ up to $z=1.3$ and becoming the first radial BAO experiment to reach Stage IV. J-PAS will detect $7\times 10^5$ galaxy clusters and groups, setting constrains on Dark Energy which rival those obtained from its BAO measurements. Thanks to the superb characteristics of the site (seeing ~0.7 arcsec), J-PAS is expected to obtain a deep, sub-arcsec image of the Northern sky, which combined with its unique photo-z precision will produce one of the most powerful cosmological lensing surveys before the arrival of Euclid. J-PAS unprecedented spectral time domain information will enable a self-contained SN survey that, without the need for external spectroscopic follow-up, will detect, classify and measure $\sigma_z\sim 0.5\%$ redshifts for $\sim 4000$ SNeIa and $\sim 900$ core-collapse SNe. The key to the J-PAS potential is its innovative approach: a contiguous system of 54 filters with $145\AA$ width, placed $100\AA$ apart over a multi-degree FoV is a powerful "redshift machine", with the survey speed of a 4000 multiplexing low resolution spectrograph, but many times cheaper and much faster to build. The J-PAS camera is equivalent to a 4.7 sq.deg. "IFU" and it will produce a time-resolved, 3D image of the Northern Sky with a very wide range of Astrophysical applications in Galaxy Evolution, the nearby Universe and the study of resolved stellar populations., Comment: 215 pages, 70 figures. J-PAS "Red Book", containing a description of the technical aspects of the Survey and its main scientific goals

In the brane-world scenario, our universe is understood as a three dimensional hypersurface embedded in a higher dimensional space-time. The fluctuations of the brane along the extra dimensions are seen from the four-dimensional point of view as new fields whose properties are determined by the geometry of the extra space. We show that such branon fields can be massive, stable and weakly interacting, and accordinlgy they are natural candidates to explain the universe missing mass problem. We also consider the possibility of producing branons non-thermally and their relevance in the cosmic coincidence problem. Finally we show that some of the branon distinctive signals could be detected in future colliders and in direct or indirect dark matter searches., Comment: 4 pages, 1 figure. To be published in the Proceedings of the XXXIX Rencontres de Moriond 'Exploring the Universe' (March 28-April 04, 2004, La Thuile, Italy)