Hecho con Indico
v3.2.5
The striking discovery that the Cosmic expansion is accelerating has turned into one of the puzzles in Cosmology sparking large observational campaigns to map the geometry and the large-scale structure of the Universe across cosmic time. I will review this effort and then discuss The Dark Energy Survey (DES), a state-of-the-art galaxy survey designed to map the positions and shapes for 300 million galaxies up to redshift >~ 1 over 5000 deg2, the light-curves of several thousand supernovae, and the masses of tens of thousands of galaxy clusters. I will present the cosmological analysis from the first year of data, mainly from the combination of clustering and weak gravitational lensing, putting them in context with those from other current and future survey datasets.
I will provide a new interpretation for the Bayes factor combination used in the DES first year analysis to quantify the tension between the Dark Energy Survey (DES) and Planck datasets. The ratio quantifies a Bayesian confidence in our ability to combine the datasets. This interpretation is prior-dependent, with wider prior widths boosting the confidence. I therefore propose that if there are any reasonable priors which reduce the confidence to below unity, then we cannot assert that the datasets are compatible. Computing the evidence ratios for the DES first year analysis and Planck, given that narrower priors drop the confidence to below unity, I conclude that DES and Planck are, in a Bayesian sense, incompatible under ΛCDM. Additionally, I compute ratios which confirm the consensus that measurements of the acoustic scale by the Baryon Oscillation Spectroscopic Survey (BOSS) are compatible with Planck, whilst direct measurements of the acceleration rate of the Universe by the SH0ES collaboration are not. I propose a modification to the Bayes ratio which removes the prior dependency using Kullback-Leibler divergences, and using this statistical test find Planck in strong tension with SH0ES in moderate tension with DES, and in no tension with BOSS. I propose this statistic as the optimal way to compare datasets, ahead of the next DES data releases, as well as future surveys. Finally, as an element of these calculations, I introduce in a cosmological setting the Bayesian model dimensionality, which is a parameterisation-independent measure of the number of parameters that a given dataset constrains.
The current data favour metastability of the electroweak (EW) vacuum, which poses a number of cosmological challenges. We suggest a novel solution which does not employ any extra fields beyond the inflaton. We show that the Higgs mixing with an inflaton can lead to a stable EW vacuum. A trilinear Higgs–inflaton coupling always results in such a mixing and it is generally present in realistic models describing the reheating stage correctly. We find that cosmological constraints on this coupling are weak and an order one mixing is possible. In this case, the model is effectively described by a single mass scale of the EW size, making it particularly interesting for direct LHC searches.
Unified Dark Matter models (UDM), a class of models that entertains the possibility of a universe where dark matter and dark energy exist as a single fluid, are an alternative approach to ${{slash}}Lambda$CDM. In this work we focus on a model with a fast transition between dark matter-like and dark energy-like behaviours. We have tested this UDM model against SNe Ia, BAO, CMB and weak lensing data. At the end of our analysis, we were able to conclude, for the first time, that this model is able to form structure and that this is in agreement with recent observational data, rendering the model as a viable alternative to ${{slash}}Lambda$CDM.
In this talk we explore the consequences of inferring cosmological parameters with uncertain theory predictions in which we include potential biases and noise sources. We will discuss that noise sources in the theory prediction translate into scatter noise in the likelihood and will provide an estimation of this quantity. We will show issues that might appear if trying to estimate parameters from such likelihood and suggest the use of Gaussian processes to reconstruct it. Furthermore, we introduce an iterative process based on Bayesian optimization to explore the cosmological parameter space in an efficient and effective manner. Finally, we will discuss and quantify the potential biases appearing when using a N-body simulation as the theory prediction for the galaxy clustering parameter estimation.
One of the fundamental assumptions of the standard LCDM cosmology is that, on large scales, all the matter-energy components of the Universe share a common rest frame. This seems natural for the visible sector, that has been in thermal contact and tightly coupled in the primeval Universe. The dark sector, on the other hand, does not have any non-gravitational interaction known to date and therefore, there is no a priori reason to impose that it is comoving with ordinary matter. In this work we explore the consequences of relaxing this assumption and study the cosmology of non-comoving fluids. We show that it is possible to construct a homogeneous and isotropic cosmology with a collection of fluids moving with non-relativistic velocities. Our model extends LCDM with the addition of a single free parameter eta_0, the initial velocity of the visible sector with respect to the frame that observes a homogeneous and isotropic universe. This modification gives rise to a rich phenomenology, while being consistent with current observations for eta_0<1.6e-3 n (95% CL). Among the observable effects we find: sizeable modifications in the density-velocity and density-lensing potential cross-correlation spectra for matter, violations of CMB statistical isotropy and production of vorticity and cosmological magnetic fields through new couplings between scalar and vector modes.
I will review the present status of the search for primordial black holes as the main component of dark matter and will describe future prospects.
One of the most mysterious and abundant components of the current known universe is the so called Dark Matter. While we usually resort to physics beyond the Standard Model and new particles as possible explanations for it, we may not need to do so at all. Black Holes formed during or after inflation (thus "primordial") could end up being the majority of the Dark matter, thus solving the issue with already well known physics. After the discovery of gravitational waves by LIGO, there's been a lot of focus on Intermediate Mass Black Holes of more than 10 solar masses, and after various tests it is currently believed they could not make up more than 1% of the DM. However, as different experiments continue to probe these possibilities, one window in much smaller masses still remains. PBHs of masses around 1 pico solar mass are small enough to not have any noticeable dynamical effect, while their size makes most lensing experiments ineffective. Thus, they could still make up the entirety of DM. One of the few ways in which such a small objects could be probed would be in their capture by bigger astrophysical objects, in particular by main sequence stars. In this talk I will share specific results obtained when modelling this scenario, showcasing how in the early universe the capture of such objects would be pretty common. This would effect heavily the star formation history of the early universe and impact the population of extremely old stars. Existing and future searches in PoP III stars could thus constrain or confirm the leftover window.
Galaxy Surveys provide an important cosmological probe to study dark energy and structure formation in the Universe. The cosmological content is however encoded in biased tracers of the non-linear evolved cosmic density field. The analysis of such data is complex and requires non-Gaussian posterior distribution functions (PDFs). Sampling such PDFs can be done within a Bayesian framework at the expense of heavy computations using, for instance, a Hamiltonian Monte Carlo Sampling algorithm. We suggest here to dramatically speed up these schemes by implementing a higher order Hamiltonian Monte Carlo scheme, demonstrating, with a lognormal-Poisson model, that the correlation length between samples and the computational cost can be reduced by an order of magnitude. This scheme has been implemented in a Bayesian framework, including structure formation with Lagrangian perturbation theory, yielding accurate reconstructions of the primordial density field associated to a distribution of galaxies, as obtained from galaxy surveys.
Pre-recombination physics imprinted the Baryon Acoustic Oscillation (BAO) feature on the matter distribution and therefore on the galaxy statistics we observe today. This known-size BAO scale let cosmological surveys study the accelerated expansion of the Universe and the unknown component that generates it. Present surveys make use of 2-point correlations function to study galaxy distribution and different fitting methods have been developed in order to reveal the BAO scale. Here we present a analytical full-shape fitting method for the angular correlation function of galaxies from the Dark Energy Survey Y1 data, and how the method compares with the fiducial DES BAO results.
We study the viability of the detection of the primordial polarization B-mode of the cosmic microwave background (CMB) from the ground, but operating on the microwave low-frequency range (e.g., from 10GHz-120GHz). The reason to choose this frequency range is twofold: one the one hand, the instrumental costing is, in principle, lower than at higher frequencies and, on the other hand, it could serve as a complement to future satellite missions like LiteBIRD, which cover frequencies above 40GHz. As it is well-known, the detection of this signal is challenging from the data analysis point of view, due to the relative low amplitude compared to foregrounds, the lensing contamination coming from the leakage of E-modes, and the instrumental noise. Our component separation approach grounds on a full-parametric maximum likelihood method to retrieve the polarized CMB, which also characterise the residual foregrounds at the angular power spectrum level. The sky simulations include galactic emission from synchrotron, dust (which are the main foreground contaminants to the polarized CMB) as well as the anomalous microwave emission (AME). We explore different configurations of the distribution of the frequency channels, in order to find an optimal instrumental design, and taking into account the limitations imposed by the atmosphere. We show that this kind of experiments are feasible and able to provide a clear detection of primordial B-modes corresponding to a tensor-to-scalar ratio parameter of r~0.002, when a delensing of around 50% is assumed.
We present a new determination of the evolving spectral energy distribution of the Extragalactic Background Light (EBL) purely based on galaxy data. Our calculations use multiwavelength observations from the ultraviolet to the far-infrared (far-IR) of a sample of aproximately 150,000 galaxies detected up to z~6 from the five fields of the Cosmic Assembly Near-Infrarred Deep Extragalactic Legacy Survey (CANDELS). These unprecedented data allow us to reduce existing uncertainties in the far-IR contribution and to improve the evolution with redshift relative to current EBL models. From our estimates, we can also derive other fundamental cosmological properties of the Universe such as the cosmic star formation history and the evolution of the galaxy luminosity densities.
We briefly review the general insight into the indirect searches of dark matter. In particular, we focus on the multi-TeV dark matter candidate among other weak interactive massive particles. We present both the state-of-the-art on this sub-eld and recent sensitivity analyses for the Square Kilometer Array (SKA) and the Cerenkov Telescope Array (CTA). We discuss the model independent approach and we show some application for branon dark matter as thermal candidate at TeV energy scale. We discuss open questions and experimental limitations.
We are in the middle of a pause. While we ponder the results of the Planck mission and a host of probes of large scale structure, and while we wait for a host of new larhe scale surveys - Euclid, LSST, DESI, to name a few - we can take stock of where we are in our understanding of the late time evolution of the Universe. I will discuss where we are in terms of theory and talk about a few of the odd, unexplained, tensions between different data sets.
The Cosmological Principle is applied to a 5D Ricci-flat (bulk) manifold. The general solution is given explicitly in the form of a single metric, namely ‘M-metric’, for every sign of the space curvature, both in the 4+1 and the 3+2 case. Friedmann-Robertson-Walker (FRW) metrics are obtained by projecting the ‘mother’ M-metric onto specific 3+1 (brane) hypersurfaces (top-down approach). This Kaluza-Klein formalism allows a very intuitive (graphical) approach to the problem of the origin of the Universe. Apart from the standard Big Bang paradigm, one can easily build models for emergent universes (arising from a quasi-stationary state) or even for models with a dynamical signature change, in the philosophy of the Hartle-Hawking ‘no boundary’ approach. A simple toy model is presented, showing a ‘Big unfreeze’ transition from a Riemannian (4D) to a pseudo-Riemannian (3+1) manifold with a radiation-dominated behavior at the beginning of time and a Cosmological-constant asymptotic behavior in the final expansion stage.
It has been shown that the longitudinal mode of a massive vector boson can be produced by inflationary fluctuations and account for the dark matter content of the Universe. In this work we examine the possibility of instead producing the transverse mode via the coupling ϕFF̃ between the inflaton and the vector field strength. Such a coupling leads to a tachyonic instability and exponential production of one transverse polarization of the vector field, reaching its maximum near the end of inflation. We show that these polarized transverse vectors can account for the observed dark matter relic density in the mass range μeV to hundreds of GeV. We also find that the tachyonic production mechanism of the transverse mode can accommodate larger vector masses and lower Hubble scales of inflation compared to the production mechanism for the longitudinal mode via inflationary fluctuation.
One possible and natural derivation from the collisionless cold dark matter (CDM) standard cosmological framework is the assumption of the existence of interactions between dark matter (DM) and photons or neutrinos. Such interacting DM models would imply a suppression of small-scale structures due to a large collisional damping effect and can help alleviate alleged tensions between standard CDM predictions and observations at small mass scales. In this talk, I will present the properties of DM subhalos formed in a high-resolution cosmological N-body simulation specifically run within these alternative models. I will also compare our results with the one obtained in the standard cosmological scenario. These results have a direct application on studies aimed at the indirect detection of DM where subhalos are expected to boost the DM signal when the CDM model is assumed. I will briefly investigate its role in the interacting DM model presented in this talk.
In this talk, we present Cherenkov Telescope Array (CTA) prospects for WIMP dark matter (DM) indirect detection through very-high-energy gamma rays originated from DM annihilations in low-mass Galactic DM subhalos. Given their masses, these are not expected to host gas/stars at all and would thus appear in the sky as unidentified gamma-ray sources (unIDs). By using the latest instrumental response functions available, we simulate CTA observations under different array configurations and pointing observation strategies, such as the scheduled CTA Extragalactic Survey. We then predict the sensitivity of CTA to dark subhalos for such scenarios, for which we also use results from N-body cosmological simulations to predict subhalo annihilation fluxes. In the absence of a DM signal, we obtain limits to the DM annihilation cross section as a function of the mass of the WIMP. We do so by also studying and proposing the best type of observation strategy that would be needed in order to derive the best achievable constraints. Our prospects are competitive to those expected for other DM targets, such as dwarf galaxies and galaxy clusters.
The Planck Mission from ESA has recently provided the best available full-sky intensity and polarization CMB data, covering a range of frequencies from 30 to 857 GHz. In this talk I will give an overview of the main Planck legacy results, which currently provide our strongest constraints on the parameters of the standard cosmological model. I will also briefly review the current and future efforts towards the measurement of the primordial B-mode of polarization, whose detection would provide a unique evidence of inflation.
We propose a novel scenario for the detection of radio signals from axionic halo dark matter. Axions or axion-like particles produce radio waves via spontaneous decay into two photons. In addition, stimulated emission by a background containing photons of identical wavelength enhances the rate of photon emission by axionic decay. A photon background generated by a bright radio source should produce a countersource that we designate as axion gegenschein, a phenomenon characterised by an echo wave of the photons emitted by an astrophysical source observable in the sky direction opposite to the source. We discuss the expected flux of this signal which future-generation radio facilities, such as SKA and HIRAX, could be sensitive to, and show relevant bounds for the gegenschein emission that can be obtained.
The PAU Survey (PAUS) is an imaging survey using a 40 narrow-band filter camera, named PAUCam. Images obtained with the PAUCam suffer from scattered light: an optical effect where light appears where it is not intended to be. Scattered light is not a random effect, it can be predicted and corrected for. Nevertheless, currently, around 8% of the PAUS flux measurements are flagged as scattered light affected and removed. Moreover, failures to flag scattered light result in photometry and photo-z outliers. With the aim of understanding and predicting scattered light, we have built BKGnet, a deep neural network for background prediction. BKGnet is trained with 120x120 pixel stamps and their corresponding positions on the CCD. To benchmark the BKGnet performance, we have developed an skyflat correcting method to remove the effect of scattered light on images. On PAUCam images on the COSMOS field, we get a 28% improvement on average with BKGnet compared with the skyflat correction method.
Cosmic voids gravitationally lens the cosmic microwave background (CMB) radiation, resulting in a distinct imprint on degree scales. We aimed to probe the consistency of simulated ΛCDM estimates and observed imprints of voids identified in the first year data set of the Dark Energy Survey (DES Y1). In particular, we intended to explore other aspects of the previously reported excess integrated Sachs-Wolfe (ISW) signal associated with cosmic voids in DES Y1 as lensing is sourced by the gravitational potential, whereas ISW depends on its time derivative. We used a simulated CMB lensing convergence map to find the optimal strategy to extract the lensing imprints given different void types and galaxy tracer density. We then stacked the Planck lensing convergence map on locations of voids identified in DES Y1 data and found a negative signal associated with DES voids that is consistent with simulations. In this presentation, I will discuss the most important aspects of our measurements and provide some prospects for the constraining power of future DES data.
Total density of the Universe is very close to the critical density; that is, the matter-energy content is exactly that required in the Universe to be flat. This strange coincidence ('flatness problem') has not yet been explained, as well as the nature of dark energy, which compensates the gavitational force caused by the matter. To explain the origin of the dark energy, this works uses a space-time whose expansion does not depend on the matter-energy content (Monjo 2017, 2018). From a topological viewpoint, it is possible to apply an homeomorphism between an expanding 3-sphere (hypercone) and a flat spacetime. If an observer is added to measure distances from the expanding and positively curved timespace, a radial deformation of the distances is found. This deformation becomes an apparent acceleration when a family of stereographic projections is applied to the flat manifold. Comparing with the standard model, a predicted value of the dark energy density (Omega_L = 0:6937181(2)) is obtained from the unique real solution of the stereographic projections when the arc length is used. References: Monjo, R. (2018). Geometric interpretation of the dark energy from projected hyperconical universes. Physical Review D 98, 043508 (LS16206D). DOI: 10.1103/PhysRevD.98.043508. arXiv:1808.09793. Monjo, R. (2017). Study of the observational compatibility of an inhomogeneous cosmology with linear expansion according to SNe Ia. Physical Review D 96, 103505. DOI: 10.1103/PhysRevD.96.103505. arXiv:1710.09697.
Using the formalism of quantum field theory in curved spacetimes, we study semiclassical effects in geometries which get close to the formation of an event horizon. These geometries are such that they imprint special features on the quantum vacuum of the fields. Specifically, we will present a series of asymptotically flat, spherically symmetric spacetimes which get close to the formation of a horizon (representing matter which gets close to crossing its Schwarzschild radius), and calculate the values of the renormalized stress-energy tensor for the $in$ vacuum state. We will also obtain the values of the effective temperature function of the outgoing fluxes of radiation, a generalization of Hawking temperature introduced in extit{Barcelu00f3 et al. PRD83, 041501(R)} (2011), which allows for a comparison of values of the renormalized stress-energy tensor between the $in$ state and the referential static Boulware vacuum state (this latter having a divergence at the Schwarzschild radius). This allows us to identify the dynamical characteristics of the spacetimes for which back-reaction of the quantum field on the geometry may be large enough to lead to significant deviations from a purely classical behaviour.
In this talk I will make a sort review on alternative theories of gravity with torsion along with a brief statement for their motivation. Then, I will focus my speech on Lagrangian densities quadratic in the curvature and torsion tensors, as they are known to produce a dynamic torsion field. By assuming that General Relativity should be recovered when the torsion vanishes and investigating the behaviour of the vector and pseudo-vector torsion fields in the weak-gravity regime, I will present a set of necessary conditions for the stability of these theories.
Regardless of the precise nature of dark matter (DM), its distribution in the central regions of galaxies remains poorly constrained at present. In particular, DM halos may be significantly affected by the presence of central supermassive black holes, leading to the possible formation of high density spikes. Two objects are of particular interest in this context: Sgr A at the center of the Milky Way, where precision astrometry and spectroscopy provide a direct probe of the gravitational potential, and M87 at the center of the M87, which is a prime target of the Event Horizon Telescope, being the first ever black hole observed directly. I will discuss different avenues that can shed light on the characteristics of the DM distribution in the cores of galaxies and the underlying properties of DM candidates. I will focus in particular on the kinematics of the S2 star at the Galactic center––which constrains the amount of dark mass around Sgr A––and electromagnetic signatures of DM annihilation on the shadow of M87
The Cosmic Microwave Background (CMB) temperature and polarization anisotropy measurements from the Planck mission have provided a strong confirmation of the LCDM model of structure formation. However, there are a few interesting tensions with other cosmological probes that leave the door open to possible extensions to LCDM. I will review some extended cosmological scenarios, in order to find a new concordance model that could explain and relieve tensions in current cosmological data.
In this work, we explore the possibility of topological defects as viable dark matter candidates. The non-thermal production of magnetic monopoles by a phase transition is studied. The Kibble mechanism is analyzed, concluding that it is not a good approach to estimate their abundance and studying the corrections of the Kibble-Zurek model. We also study the effect of monopoles annihilation within this framework. The result of this analysis is that monopoles with a mass around the PeV provide a density compatible with PLANCK observations of the present dark matter density In addition, recent observations of high energy neutrinos by IceCube show an spectrum that is not compatible with a power law that would be expected in a standard astrophysical scenario. We study the possibility that a decaying dark monopole with a mass in the PeV range provides a promising interpretation of the observed spectrum.
In flat spacetime, an instability problem arises in the homogeneous field configuration of a system with concave potential. We extend that analysis to an accelerated expanding universe where the potential is not needed to be concave in order to have instabilities. We study the particular case of an inflationary universe with a slow-roll phase and calculate the lifetime associated to its decay. In order to avoid this instability problem, with an estimation of the size of the observable universe at this epoch we obtain an upper bound for the Hubble parameter which is incompatible with standard models of inflation based on a minimally coupled scalar inflaton.
In warm inflation, substantial radiation production can occur concurrently with the inflationary expansion. In the strong dissipative regime, the temperature dependent dissipative coefficient leads to the wrong spectral index. An imperfect radiation fluid, via shear effects, can successfully solve that problem, although one needs to resort to weakly interacting fluids. However, certain modified gravity models mimic shear effects. This encourages us to consider an f(phi,R) theory in warm inflation, and study its effects on the power spectrum of primordial perturbations.
In this talk I will present a new modified theory of gravitation, that includes infinite derivatives and torsion in the action. I shall also provide some solutions that are ghost and singularity free.
In this talk we shall consider the possibility of chiral symmetry restoration for observers located close to acceleration horizons, black holes and cosmological horizons. The Thermalization Theorem formalism and the large N limit (with N being the number of pions) will be employed to solve the lowest-order approximation to QCD at low energies in Rindler spacetime and close to the horizons of de Sitter and Schwarzschild. We shall show that chiral symmetry is restored in these cases, in complete analogy with the Minkowski-spacetime, finite-temperature case.
Although the Lambda cold dark matter model (ΛCDM) has become the best phenomenological description for the late-time accelerating phase of the Universe, the yet unsolved cosmological constant problem has driven an effort towards alternatives. We will mention two leading approaches which avoid the introduction of a cosmological constant. On the one hand, Dark Energy (DE) models where yet unobserved scalar fields would dominate the energy content at late times, avoiding fine-tuning issues as well as accelerating the Universe. On the other hand, there are Modified Gravity (MG) models that instead modify the current theory of gravity. We will demonstrate how to work out solutions to the perturbations equations in MG and DE models under the sub-horizon approximation. We will see that one can derive analytical solutions for DE perturbations and test them numerically showing that the quasi-static approximation actually performs quite well for this kind of models. Using the latter and simple modifications to the CLASS Boltzmann code, which we call EFCLASS, in conjunction to very accurate analytic approximations for the background evolution, one can obtain competitive results in a much simpler and less error-prone approach. We then use the aforementioned models to derive constraints from the latest cosmological data, including Type Ia supernovae, Baryon Acoustic Oscillations (BAO), Cosmic Microwave Background (CMB), H(z) and growth-rate data, and find they are statistically consistent to the ΛCDM model.
I will briefly outline the first progresses with miniJPAS, the JPAS-like data obtained with the Pathfinder camera attached to the JST/T250 telescope at the OAJ. This small data set already encodes all the richness and complexity to be expected for regular J-PAS data, and allows defining the hottest science cases to be addressed with the main survey. I will also describe the strategy for J-PAS during the immediate, exciting months to come in the near future.
The next generation of galaxy surveys will allow us to test one of the most fundamental assumptions of the standard cosmology, i.e., that gravity is governed by the general theory of relativity (GR). In this paper we investigate the ability of the Javalambre Physics of the Accelerating Universe Astrophysical Survey (J-PAS) to constrain GR and its extensions. Based on the J-PAS information on clustering and gravitational lensing, we perform a Fisher matrix forecast on the effective Newton constant, $\mu$, and the gravitational slip parameter, $\eta$, whose deviations from unity would indicate a breakdown of GR. Similar analysis is also performed for the DESI and Euclid surveys and compared to J-PAS with two configurations of area, namely an initial expectation with 4000 $\mathrm{deg}^2$ and the future best case scenario with 8500 $\mathrm{deg}^2$. We show that J-PAS will be able to measure the parameters $\mu$ and $\eta$ at a sensitivity of $2\% - 7\%$, and will provide the best constraints in the interval $z = 0.3 - 0.6$, thanks to the large number of ELGs detectable in that redshift range. We also discuss the constraining power of J-PAS for dark energy models with a time-dependent equation-of-state parameter of the type $w(a)=w_0+w_a(1-a)$, obtaining $\Delta w_0=0.058$ and $\Delta w_a=0.24$ for the absolute errors of the dark energy parameters."
We compare the statistics and morphology of arcs in galaxy clusters using simulations with standard cold dark matter and simulations where dark matter has a probability of interaction (parametrized by its cross section), i.e self-interacting dark matter. Through ray tracing, we produce a statistically large number of arcs around galaxy clusters at different redshifts. Since dark matter in more likely to interact in colliding clusters than in relaxed clusters, and this probability of interaction is largest in the denser regions, we focus our analysis on radial arcs (which trace the lensing potential in the central region better than tangential arcs), in galaxy clusters which are undergoing a major merger. We find that self-interacting dark matter produces fewer radial arcs than standard cold dark matter but they are on average more magnified. We also appreciate differences in the morphology which could be used to statistically favor one model versus the other.
Dark matter, as a cold collisionless fuid, effectively occupies a three-dimensional sub-manifold in six-dimensional phase space. In simulations, this "dark matter sheet" can in principle be reconstructed by interpolation techniques to obtain an almost exact density estimate. However, in regions of strong mixing (like dark matter haloes), this is difficult due to the rapid growth of the sheet's complexity and an alternative is required. I will present a hybrid scheme which uses sheet-interpolation-techniques where a reconstruction is possible, and N-body-techniques in regions of strong mixing. This makes possible warm dark matter simulations that are reliable inside low- and high-density regions for the first time.
We study the dependence of a variety of halo properties (shape, spin, virialisation status) on different environments in a whole-sky ΛCDM light-cone halo catalogue extending to z ∼ 0.65,CDM light-cone halo catalogue extending to z ∼ 0.65, 0.65, using a simple and well-defined halo isolation criterion. Using this definition of the environment we study if and how the DM halo-properties and their interrelations depend on their environment. We also study the relative orientations of the spin- and shape- vectors of DM halos with their isolation, as well as the alignment of the shape- and the spin- vectors of neighbouring DM halos for a vast range of separations. Lastly, we focus on halo pairs, which are encountered in a variety of isolation states in our catalogue and, specifically, we study how the shape- and spin- alignments of halo-pairs is dependent on the isolation of the pair. The latter can give insight in the formation and evolution of halos formed under the dynamical interaction of their nearest neighbour in a region devoid of other massive halos, i.e. not affected by the ambient tidal field.
If dark matter particles annihilate, then we should detect signals of this annihilation in the sky. In this talk we will focus on the contribution of particle dark matter in the injection of cosmic rays in dwarf spheroidals and the synchrotron emission from secondary processes. We also study the Square Kilometre Array (SKA) sensitivity in the detection of dark matter candidates that would fit the AMS positron fraction and the gamma-ray signal from HESS J1745-290 .
I employ methods of fractal geometry and fluid turbulence to describe how the cosmic web structure arises in the nonlinear regime of evolution of the LCDM cosmology. I evaluate this theory with the results of N-body simulations and observations of the galaxy distribution by the Sloan Digital Sky Survey.
A generic modified gravity theory, that generates a dynamical dark energy, will produce a different evolution at the background level, determined by the DE equation of state, as well as different cosmological perturbations with respect to LCDM. An effect that is completely general to modified gravity models is that the propagation of tensor perturbations is modified so that it emerges a notion of GW luminosity distance, different from the standard electromagnetic luminosity distance. We show that this effect is a powerful probe of modified gravity, that will be tested at LISA and at 3G GW detectors such as the Einstein Telescope.
The PAU Survey (PAUS) is an innovative photometric survey with 40 narrow bands at the William Herschel Telescope (WHT). The narrow bands are spaced at 100A intervals covering the range 4500A to 8500A and, in combination with standard broad bands, enable excellent redshift precision. Using BCNz2, a new photometric redshift code developed for this purpose, we characterise the photometric redshift performance using PAUS data on the COSMOS field. Comparison to secure spectra from zCOSMOS DR3 shows that PAUS achieves sigma68 / (1+z) = 0.0037 to i < 22.5 when selecting the best 50% of the sources based on a photometric redshift quality cut. Furthermore, a higher photo-z precision sigma68 / (1+z) = 0.001 is obtained for a bright and high quality selection, which is driven by the identification of emission lines. This talk discuss the PAU survey progress, photometric redshift and application of deep learning to determine PAUS redshifts. We conclude that PAUS meets its design goals, opening up a hitherto uncharted regime of deep, wide, and dense galaxy survey with precise redshifts that will provide unique insights into the formation, evolution and clustering of galaxies, as well as their intrinsic alignments.
In this work we have considered the gravitational production as the mechanism responsible for the creation of dark matter during the early epochs of the Universe. This mechanism imposes some constrains in the parameter space of the candidate field as it abundance is bounded by the observations. We have considered the dark matter field as a scalar one not minimally coupled to gravity. The importance of the oscillations of the Ricci scalar sourced by the inflaton is investigated as it enhances the production of particles during the reheating stage.
I will summarize the progress on image simulations on LSST-DESC and their relevance for next generation cosmological surveys.
Strong lenses are systems in which the light from a background source is deflected by a foreground galaxy or group of galaxies, resulting in multiple images of the background source. These images are also usually heavily distorted, acquiring the shape of rings or arcs. Study of these images provides us unique information about the distribution of matter (baryonic plus dark) within the foreground mass acting as a lens. This information allows us, for instance, to constrain galaxy mass models, the stellar initial mass function or the abundance of dark matter subhaloes. Strong lensing is therefore a major cosmological tool. In this work we focus our attention to MACS J1206 galaxy cluster at z = 0.44 and 82 spectroscopic multiple images caused by it, which belong to 27 background galaxies at redshifts between 1.01 and 6.06. 11 of these multiple images are found within the 50 kpc of the brightest cluster galaxy (BCG) and two great arcs (one straight and other curved) can clearly be seen arising from the BCG. These are suitable conditions to use a non-parametric method, which requires a sufficiently large number of lensed images as constraints. Accordingly, we have performed a non-parametric strong lensing analysis with the positional measurements of these multiple images in order to estimate an accurate total mass distribution (with baryonic and dark components) in the center of this galaxy cluster.
The late time acceleration of the Universe can be characterized in terms of an extra, time dependent, component of the universe -- dark energy. The simplest proposal for dark energy is quintessence, a scalar field, phi, whose dynamics is solely dictated by its potential, V(phi). In this simple case, just an extra function of the background is necessary to describe the evolution of the dark energy density. We find its time dependence for a broad family of potentials. Using this information, we propose a parametrization which is accurate and in terms of which we construct physical priors for quintessence.
The late time acceleration of the Universe can be characterized in terms of an extra, time dependent, component of the universe -- dark energy. The simplest proposal for dark energy is quintessence, a scalar field, phi, whose dynamics is solely dictated by its potential, V(phi). In this simple case, just an extra function of the background is necessary to describe the evolution of the dark energy density. We find its time dependence for a broad family of potentials. Using this information, we propose a parametrization which is accurate and in terms of which we construct physical priors for quintessence.
Galaxy clustering is one of the main cosmological probes used by the Dark Energy Survey to investigate the nature of the Dark Energy. In order to avoid biasing our measurements derived from galaxy clustering, the impact of observing conditions must be taken into account, since they can imprint a non-cosmological clustering signal. These observing conditions are characterized through the creation of and Survey Property maps (SPs) which are used to mitigate their contamination. The aim of this contribution is to showcase how the influence of these SPs on the clustering is identified and to explain the procedure that is followed to reduce their impact.
The QUIJOTE (Q U I JOint TEnerife) CMB Experiment operates from the Teide Observatory, providing a novel view of the northern sky in the frequency range from 10 to 20 GHz with the Multi Frequency Instrument (MFI). Moreover, it is targeting the detection of the B-modes in the polarization of the CMB at 30 and 40 GHz with the Thirty-Forty GHz Instrument (TFGI), with a tensor to scalar ratio goal of r=0.05. While the TFGI is in commissioning phase, the MFI, in operations since November 2012, has been observing some specific galactic regions (Génova-Santos el al. (2015), Génova-Santos el al. (2017), Poidevin et al. (2018)) but also the whole northern sky, allowing us to produce wide-survey maps of the I Q and U Stokes parameters, at 11, 13, 17 and 19 GHz. These maps are a unique view of the low frequency radio foregrounds in intensity and in polarization, providing a new data-set for the characterization of the synchrotron emission at large angular scales and of the Anomalous Microwave Emission (AME), a dust-correlated emission whose origin is still uncertain. All the maps are going to be published and available for the scientific community in the coming months. In this talk, I would like to give a brief overview of QUIJOTE, present the wide-survey maps, and mention about the preliminary scientific results achieved with the maps.
The nature of dark matter (DM) is still an open question for modern physics. In the particle DM paradigm, this elusive kind of matter cannot be made of any of the known particles of the Standard Model (SM). Many efforts have been made in order to model the nature of the DM. Among others, and beyond the SM of particle physics, we focus on brane world theory as a prospective framework for DM candidates. Branons are new degrees of freedom that appear in flexible brane-world models corresponding to brane fluctuations. They are a natural DM candidate, because branons behave as weakly interacting massive particles (WIMPs), that are one of the most favored candidates for DM. The ground-based gamma-ray telescope MAGIC could potentially detect DM indirectly, by observing secondary products of its annihilation into SM particles. In this contribution, we set constraints on branon DM from already published observations of dwarf spheroidal galaxies with the MAGIC Telescopes, by using a full likelihood analysis.
In this talk, we present our studies of the discovery potential of low-mass Galactic dark matter (DM) subhalos for indirect searches of DM. In particular, we analyzed the properties of DM halo substructure in a galaxy like our own. To do so, we have used data from the Via Lactea II (VL-II) N-body cosmological simulation, that resolves subhalos down to one million solar masses. First, we characterized the abundance, distribution and structural properties of the VL-II subhalo population. Then, we repopulated the original simulation with millions of subhalos of masses down to four orders of magnitude the nominal VL-II particle resolution. In a final step, we computed mean subhalo DM annihilation fluxes for the entire subhalo population, for which we created hundreds of VL-II realizations. Our results show that low-mass Galactic subhalos (including those not massive enough to retain stars/gas) may yield annihilation fluxes comparable to those expected from other, more acknowledgeable DM targets like dwarf galaxies. Thus, small subhalos may play a very relevant role in current and future indirect DM searches such as those performed in gamma rays from both the ground and space.
As high redshift galaxies cannot be resolved, it is necessary to have the information of the whole stellar population in order to interpret correctly the data. Thus, templates of spectra of simple stellar populations (SSPs) are needed to extract information about the stellar populations. We present our new high resolution spectra of SSPs. We have tested the application of the spectra testing the evolution of the color-color diagrams.
A prediction of the standard LCDM cosmological model is that dark matter (DM) halos are teeming with numerous self-bound substructure, or subhalos. The most massive ones host the observed dwarf satellite galaxies, while smaller subhalos may host no stars/gas at all and thus may have no visible astrophysical counterparts and would remain completely dark. Yet, some of these ‘dark satellites’ are expected to be excellent targets for gamma-ray DM searches given their typical distances and structural properties. In this talk, I will discuss the importance that DM subhalos may have for DM searches with present or future gamma-ray observatories, such as the NASA Fermi satellite and the future Cherenkov telescope array (CTA). I will also describe the recent efforts we have made to search for dark satellites in Fermi-LAT data and to set constraints on the nature of the DM particle using these elusive targets.