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Introduction

Additional affiliations

April 2010 - present

October 1998 - September 2000

**Queen Mary, University of London**

Description

- Postdoc

## Publications

Publications (130)

The field equations of modified gravity theories, when considering a homogeneous and isotropic cosmological model, always become autonomous differential equations. This relies on the fact that in such models all variables only depend on cosmological time, or another suitably chosen time parameter. Consequently, the field equations can always be cas...

The discovery of accelerated expansion of the Universe opened up the possibility of new scenarios for the doom of our space–time, besides eternal expansion and a final contraction. In this paper, we review the chances that may await our universe. In particular, there are new possible singular fates (sudden singularities, big rip, etc.), but there a...

Combining measurements with observations of the large scale structure coming from surveys which will probe the Universe in different scale regimes as compared to the size of the horizon, is a crucial step. Cosmology is (among others) our gravity laboratory. Hence, detailed investigation of the cosmological applications of various theories of gravit...

Our standard model of the Universe offers an astounding agreement with a large number of observational features, and yet it is still unsatisfactorily fragmentary from many relevant physical perspectives: many questions remain unsolved which do not allow for a perfect match between theory and observations. For this reason, our traditional way to thi...

In this work we explore and test new formulations of cosmological scenarios in $f(Q)$ theories. In these settings, the non-metricity scalar ($Q$) is the main source of gravity and Friedmann equations are modified to account for the associated degrees of freedom. This work focuses first on the derivation, and then theoretical and observational analy...

General Relativity and the $\Lambda$CDM framework are currently the standard lore and constitute the concordance paradigm. Nevertheless, long-standing open theoretical issues, as well as possible new observational ones arising from the explosive development of cosmology the last two decades, offer the motivation and lead a large amount of research...

Over the last years some interest has been gathered by f(Q) theories, which are new candidates to replace Einstein’s prescription for gravity. The nonmetricity tensor Q allows to put forward the assumption of a free torsionless connection and, consequently, new degrees of freedom in the action are taken into account. This work focuses on a class of...

In this work, we further study a metric modified theory of gravity which contains a non-minimal coupling to matter, more precisely, we assume two functions of the scalar curvature, $f_1$ and $f_2$, where the first one generalises the Hilbert-Einstein action, while the second couples to the matter Lagrangian. On the one hand, assuming a $\Lambda$CDM...

In this work, we further study a metric modified theory of gravity which contains a non-minimal coupling to matter, more precisely, we assume two functions of the scalar curvature, $$f_1$$ f 1 and $$f_2$$ f 2 , where the first one generalises the Hilbert–Einstein action, while the second couples to the matter Lagrangian. On the one hand, assuming a...

With a focus on modified gravity this book presents a review of the recent developments in the fields of gravity and cosmology, presenting the state of the art, high-lighting the open problems, and outlining the directions of future research.
General Relativity and the ΛCDM framework are currently the standard lore and constitute the concordance pa...

Over the last years some interest has been gathered by $f(Q)$ theories, which are new candidates to replace Einstein's prescription for gravity. The non-metricity tensor $Q$ allows to put forward the assumption of a free torsionless connection and, consequently, new degrees of freedom in the action are taken into account. This work focuses on a cla...

In this work, we consider an extension of symmetric teleparallel gravity, namely, f(Q) gravity, where the fundamental block to describe spacetime is the nonmetricity, Q. Within this formulation of gravitation, we perform an observational analysis of several modified f(Q) models using the redshift approach, where the f(Q) Lagrangian is reformulated...

In this work, we consider an extension of symmetric teleparallel gravity, namely, $f(Q)$ gravity, where the fundamental block to describe spacetime is the nonmetricity, $Q$. Within this formulation of gravitation, we perform an observational analysis of several modified $f(Q)$ models using the redshift approach, where the $f(Q)$ Lagrangian is refor...

In this work we study a phenomenological generalization of the Chaplygin cosmological model, which we call umami Chaplygin model. We consider three different cosmological background scenarios in which our fluid can play three different roles: only as a dark energy component; as a dark matter and dark energy component; and as a dark plus baryonic ma...

In this work we study in detail a phenomenological generalization of the Chaplygin cosmological model, which we call as \textit{umami} Chaplygin model. We consider three different cosmological background scenarios in which our fluid can play three different roles: only as a dark energy component; as a dark matter and dark energy component; and as a...

The study of the dynamics of a two-body system in modified gravity constitutes a more complex problem than in Newtonian gravity. Numerical methods are typically needed to solve the equations of geodesics. Despite the complexity of the problem, the study of a two-body system in f (R) gravity leads to a new exciting perspective hinting the right stra...

The study of the dynamics of a two-body system in modified gravity constitutes a more complex problem than in Newtonian gravity. Numerical methods are typically needed to solve the equations of geodesics. Despite the complexity of the problem, the study of a two-body system in $f(R)$ gravity leads to a new exciting perspective hinting the right str...

The {\it concordance} cosmological model has been successfully tested throughout the last decades. Despite its successes, the fundamental nature of dark matter and dark energy is still unknown. Modifications of the gravitational action have been proposed as an alternative to these dark components. The straightforward modification of gravity is to g...

Alternative theories of gravity may serve to overcame several shortcomings of the standard cosmological model but, in their weak field limit, they must recover General Relativity to match the tight constraints at Solar System scale. Therefore, testing such alternative models at scale of stellar systems could give a unique opportunity to confirm or...

We have selected a sample of eleven massive clusters of galaxies observed by the Hubble Space Telescope in order to study the impact of the dynamical state on the IntraCluster Light (ICL) fraction, the ratio of total integrated ICL to the total galaxy member light. With the exception of the Bullet cluster, the sample is drawn from the Cluster Lensi...

It is a very well established matter nowadays that many modified gravity models can offer a sound alternative to General Relativity for the description of the accelerated expansion of the universe. But it is also equally well known that no clear and sharp discrimination between any alternative theory and the classical one has been found so far. In...

The cold dark matter (CDM) paradigm successfully explains the cosmic structure over an enormous span of redshifts. However, it fails when probing the innermost regions of dark matter halos and the properties of the Milky Way's dwarf galaxy satellites. Moreover, the lack of experimental detection of Weakly Interacting Massive Particle (WIMP) favors...

The cosmological redshift drift could lead to the next step in high-precision cosmic geometric observations, becoming a direct and irrefutable test for cosmic acceleration. In order to test the viability and possible properties of this effect, also called Sandage-Loeb (SL) test, we generate a model independent mock data set so as to compare its con...

Light Axionic Dark Matter, motivated by string theory, is increasingly favored for the "no-WIMP era". Galaxy formation is suppressed below a Jeans scale, of $\simeq 10^8 M_\odot$ by setting the axion mass to, $m_B \sim 10^{-22}$eV, and the large dark cores of dwarf galaxies are explained as solitons on the de-Broglie scale. This is persuasive, but...

The clustering amplitude of 7143 clusters from the Sloan Digital Sky Survey (SDSS) is found to increase linearly with cluster mass, closely agreeing with the Gaussian random field hypothesis for structure formation. In detail, the observed correlation length exceeds pure cold dark matter (CDM) simulation predictions by $\simeq 6\%$, for the standar...

In the Physics Degree it is of fundamental importance to practice in an Experimental Laboratory. The standard Laboratory Sessions consist of two main parts: data handling and data processing. The session should also have a prologue, where students get to know the underlaying theory of the practical session and an epilogue, where students present th...

Using Planck satellite data, we construct SZ gas pressure profiles for a large, volume-complete sample of optically selected clusters. We have defined a sample of over 8,000 redMaPPer clusters from the Sloan Digital Sky Survey (SDSS), within the volume-complete redshift region 0.100 < z < 0.325, for which we construct Sunyaev-Zel'dovich (SZ) effect...

We present accurate photometric redshifts for galaxies observed by the Cluster Lensing and Supernova survey with Hubble (CLASH). CLASH observed 25 massive galaxy cluster cores with the Hubble Space Telescope in 16 filters spanning 0.2 - 1.7 $\mu$m. Photometry in such crowded fields is challenging. Compared to our previously released catalogs, we ma...

In the Physics Degree it is of fundamental importance to practice in an Experimental Laboratory. The standard Laboratory Sessions consist of two main parts: data handling and data processing. The session should also have a prologue, where students get to know the underlaying theory of the practical session and an epilogue, where students present th...

In this work we consider a family of cosmological models featuring future singularities. This type of cosmological evolution is typical of dark energy models with an equation of state violating some of the standard energy conditions (e.g. the null energy condition). Such kind of behavior, widely studied in the literature, may arise in cosmologies w...

In this work we consider a family of cosmological models featuring future singularities. This type of cosmological evolution is typical of dark energy models with an equation of state violating some of the standard energy conditions (e.g. the null energy condition). Such a kind of behavior, widely studied in the literature, may arise in cosmologies...

We construct a large, redshift complete sample of distant galaxy clusters by correlating Sloan Digital Sky Survey (SDSS) Data Release 12 (DR12) redshifts with clusters identified with the red-sequence Matched-filter Probabilistic Percolation (redMaPPer) algorithm. Our spectroscopic completeness is 97% for $\simeq$ 7000 clusters within the redMaPPer...

In [1] a new method to measure the speed of light through Baryon Acoustic
Oscillations (BAO) was introduced. Here, we describe in much more detail the
theoretical basis of that method, its implementation, and give some newly
updated results about its application to the forecast data. In particular, we
will show that SKA will be able to detect a 1%...

We explore the observational adequacy of a class of unified dark energy and dark matter (UDE/M) models with a fast transition. Our constraints are set using a combination of geometric probes—some low redshift ones and some high redshift ones (CMB-related included). The transition is phenomenologically modeled by two different transition functions c...

We present basic ideas of the varying speed of light cosmology, its formulation, benefits and problems. We relate it to the theories of varying fine structure constants and discuss some new tests (redshift drift and angular diameter distance maximum) which may allow measuring timely and spatial change of the speed of light by using the future missi...

In this work we show the results obtained applying a Unified Dark Matter (UDM) model with a fast transition to a set of cosmological data. Two different functions to model the transition are tested, and the feasibility of both models is explored using CMB shift data from Planck [1], Galaxy Clustering data from [2] and [3], and Union2.1 SNe Ia[4]. T...

In this letter we describe a new method to use Baryon Acoustic Oscillations
(BAO) to derive a constraint on the possible variation of the speed of light.
The method relies on the fact that there is a simple relation between the
angular diameter distance $(D_{A})$ maximum and the Hubble function $(H)$
evaluated at the same maximum-condition redshift...

A clean measurement of the evolution of the galaxy cluster mass function can
significantly improve our understanding of cosmology from the rapid growth of
cluster masses below z < 0.5. Here we examine the consistency of cluster
catalogues selected from the SDSS by applying two independent gravity-based
methods using all available spectroscopic reds...

A fast transition between a standard matter-like era and a late
$\Lambda$CDM-like epoch generated by a single Unified Dark Matter component can
explain the observed acceleration of the Universe. UDM models with a fast
transition should be clearly distinguishable from $\Lambda$CDM (and
alternatives) through observations. Here we focus on a particula...

In this work we investigate if a small fraction of quarks and gluons, which
escaped hadronization and survived as a uniformly spread perfect fluid, can
play the role of both dark matter and dark energy. This fluid, as developed in
\citep{Brilenkov}, is characterized by two main parameters: $\beta$, related to
the amount of quarks and gluons which a...

In this work we present a nonparametric approach, which works on minimal
assumptions, to reconstruct the cosmic expansion of the Universe. We propose to
combine a locally weighted scatterplot smoothing method and a
simulation-extrapolation method. The first one (Loess) is a nonparametric
approach that allows to obtain smoothed curves with no prior...

We review the appropriateness of using SNIa observations to detect potential
signatures of anisotropic expansion in the Universe. We focus on the two
independent datasets of SNIa provided by SNLS3 and Union2 and mainly use the
hemispherical comparison method to detect a possible anisotropic expansion. We
perform a complete analysis by making use of...

In this letter we propose a test to detect the linearity of the dark energy
equation of state, and apply it to two different Type Ia Supernova (SN Ia) data
sets, Union2.1 and SNLS3. We find that: a. current SN Ia data are well
described by a dark energy equation of state linear in the cosmic scale factor
a, at least up to a redshift z = 1, independ...

Cosmography provides a model-independent way to map the expansion history of
the Universe. In this paper we simulate a Euclid-like survey and explore
cosmographic constraints from future Baryonic Acoustic Oscillations (BAO)
observations. We derive general expressions for the BAO transverse and radial
modes and discuss the optimal order of the cosmo...

Aims. We investigate the degree of improvement in dark energy constraints
that can be achieved by extending Type Ia Supernova (SN Ia) samples to
redshifts z > 1.5 with the Hubble Space Telescope (HST), particularly in the
ongoing CANDELS and CLASH multi-cycle treasury programs.
Methods. Using the popular CPL parametrization of the dark energy, w =...

The Cluster Lensing And Supernovae survey with Hubble (CLASH) is an Hubble
Space Telescope (HST) Multi-Cycle Treasury program observing 25 massive galaxy
clusters. CLASH observations are carried out in 16 bands from UV to NIR to
derive accurate and reliable estimates of photometric redshifts. We present the
CLASH photometric redshifts and study the...

The cosmological model consisting of an electromagnetic Born-Infeld (BI) field coupled to a Robertson-Walker geometry is tested with the standard probes of SNIa, GRBs and direct Hubble parameter. The BI electromagnetic matter is adjusted to Ω
BI
= 0.037 when tested with SNIa and the Hubble parameter data (0.1 < z < 1.75); while when tested with GRB...

In the strong lensing regime non-parametric lens models struggle to achieve
sufficient angular resolution for a meaningful derivation of the central
cluster mass distribution. The problem lies mainly with cluster members which
perturb lensed images and generate additional images, requiring high resolution
modeling, even though we mainly wish to und...

In this work we set observational constraints of the Superfluid Chaplygin gas
model, which gives a unified description of the dark sector of the Universe as
a Bose-Einstein condensate (BEC) that behaves as dark energy (DE) while it is
in the ground state and as dark matter (DM) when it is in the excited state. We
first show and perform the various...

A fast transition between a standard matter-like era and a late Λcold dark matter (ΛCDM)-like epoch (or more in general, a
CDM+DE era), generated by a single unified dark matter (UDM) component, can provide a new interesting paradigm in the context
of general relativity, alternative to ΛCDM itself or other forms of dark energy (DE) or modified grav...

The cosmological model consisting of an electromagnetic Born-Infeld (BI)
field coupled to a Robertson-Walker geometry is tested with the standard probes
of SNIa, GRBs and direct Hubble parameter. The analysis shows that the
inclusion of the nonlinear electromagnetic component does not contribute in a
significative way to the observed expansion. The...

In this work we introduce two new polynomial parametrizations of dark energy and explore their correlation properties. The
parameters to fit are the equation-of-state values at z= 0 and z= 0.5, which have naturally low correlation and have already been shown to improve the popular Chevallier–Polarski–Linder
(CPL) parametrization. We test our models...

The Cluster Lensing And Supernova survey with Hubble (CLASH) is a 524-orbit Multi-Cycle Treasury Program to use the gravitational lensing properties of 25 galaxy clusters to accurately constrain their mass distributions. The survey, described in detail in this paper, will definitively establish the degree of concentration of dark matter in the clus...

Model independent reconstructions of dark energy have received some
attention. The approach that addresses the reconstruction of the dimensionless
coordinate distance and its two first derivatives using a polynomial fit in
different redshift windows is well developed
\cite{DalyDjorgovski1,DalyDjorgovski2,DalyDjorgovski3}. In this work we offer
new...

We study the possibility to extract model independent information about the
dynamics of the universe by using Cosmography. We intend to explore it
systematically, to learn about its limitations and its real possibilities. Here
we are sticking to the series expansion approach on which Cosmography is based.
We apply it to different data sets: Superno...

We analyse dark energy models where self-interacting three-forms or phantom
fields drive the accelerated expansion of the Universe. The dynamics of such
models is often studied by rewriting the cosmological field equations in the
form of a system of autonomous differential equations, or simply a dynamical
system. Properties of these systems are usu...

We examine the inner mass distribution of the relaxed galaxy cluster A383 (z = 0.189), in deep 16?band Hubble Space Telescope/ACS+WFC3 imaging taken as part of the Cluster Lensing And Supernova survey with Hubble (CLASH) multi-cycle treasury program. Our program is designed to study the dark matter distribution in 25 massive clusters, and balances...

Using real and synthetic Type Ia SNe (SNeIa) and baryon acoustic oscillations (BAO) data representing current observations forecasts, this paper investigates the tension between those probes in the dark energy equation of state (EoS) reconstruction considering the well known CPL model and Wang's low correlation reformulation. In particular, here we...

We show that a large-area imaging survey using narrow-band filters could detect quasars in sufficiently high number densities,
and with more than sufficient accuracy in their photometric redshifts, to turn them into suitable tracers of large-scale structure.
If a narrow-band optical survey can detect objects as faint as i= 23, it could reach volume...

We present a strong-lensing analysis of the galaxy cluster MACS J1206.2–0847 (z = 0.44) using UV, Optical, and IR, HST/ACS/WFC3 data taken as part of the CLASH multi-cycle treasury program, with VLT/VIMOS spectroscopy for some of the multiply lensed arcs. The CLASH observations, combined with our mass model, allow us to identify 47 new multiply len...

The Cluster Lensing And Supernova survey with Hubble (CLASH) is a 524-orbit
multi-cycle treasury program to use the gravitational lensing properties of 25
galaxy clusters to accurately constrain their mass distributions. The survey,
described in detail in this paper, will definitively establish the degree of
concentration of dark matter in the clus...

In this work we introduce two new polynomial parametrizations of dark energy
and explore their correlation properties. The parameters to fit are the
equation of state values at z=0 and z=0.5, which have naturally low correlation
and have already been shown to improve the popular Chevallier-Polarski-Linder
(CPL) parametrization. We test our models w...

We consider the Einstein equations within the DBI scenario for a spatially
flat Friedmann-Robertson-Walker (FRW) spacetime without a cosmological
constant. We derive the inflationary scenario by applying the symmetry
transformations which preserve the form of the Friedmann and conservation
equations. These form invariance transformations generate a...

We study the possibility of detecting oscillating patterns in the equation of state (EoS) of the dark energy using different cosmological datasets. We follow a phenomenological approach and study three different oscillating models for the EoS, one of them periodic and the other two damped (proposed here for the first time). All the models are chara...

Scientists working in Relativity, Gravitation and Cosmology in Spanish institutions have been organising the Spanish Relativity Meetings (ERE) for more than 30 years now, and 2009 was the turn of the group at the University of the Basque Country (UPV/EHU) to continue this well established tradition. There is no doubt these meetings have become a be...