scispace - formally typeset
Search or ask a question

Showing papers on "Cosmology published in 2016"


Journal ArticleDOI
TL;DR: In this paper, the role of torsion in gravity has been extensively investigated along the main direction of bringing gravity closer to its gauge formulation and incorporating spin in a geometric description.
Abstract: Over recent decades, the role of torsion in gravity has been extensively investigated along the main direction of bringing gravity closer to its gauge formulation and incorporating spin in a geometric description. Here we review various torsional constructions, from teleparallel, to Einstein-Cartan, and metric-affine gauge theories, resulting in extending torsional gravity in the paradigm of f (T) gravity, where f (T) is an arbitrary function of the torsion scalar. Based on this theory, we further review the corresponding cosmological and astrophysical applications. In particular, we study cosmological solutions arising from f (T) gravity, both at the background and perturbation levels, in different eras along the cosmic expansion. The f (T) gravity construction can provide a theoretical interpretation of the late-time universe acceleration, alternative to a cosmological constant, and it can easily accommodate with the regular thermal expanding history including the radiation and cold dark matter dominated phases. Furthermore, if one traces back to very early times, for a certain class of f (T) models, a sufficiently long period of inflation can be achieved and hence can be investigated by cosmic microwave background observations-or, alternatively, the Big Bang singularity can be avoided at even earlier moments due to the appearance of non-singular bounces. Various observational constraints, especially the bounds coming from the large-scale structure data in the case of f (T) cosmology, as well as the behavior of gravitational waves, are described in detail. Moreover, the spherically symmetric and black hole solutions of the theory are reviewed. Additionally, we discuss various extensions of the f (T) paradigm. Finally, we consider the relation with other modified gravitational theories, such as those based on curvature, like f (R) gravity, trying to illuminate the subject of which formulation, or combination of formulations, might be more suitable for quantization ventures and cosmological applications.

969 citations


Journal ArticleDOI
TL;DR: In this paper, the authors investigated the potential for the eLISA space-based interferometer to detect the stochastic gravitational wave background produced by strong first-order cosmological phase transitions.
Abstract: We investigate the potential for the eLISA space-based interferometer to detect the stochastic gravitational wave background produced by strong first-order cosmological phase transitions. We discuss the resulting contributions from bubble collisions, magnetohydrodynamic turbulence, and sound waves to the stochastic background, and estimate the total corresponding signal predicted in gravitational waves. The projected sensitivity of eLISA to cosmological phase transitions is computed in a model-independent way for various detector designs and configurations. By applying these results to several specific models, we demonstrate that eLISA is able to probe many well-motivated scenarios beyond the Standard Model of particle physics predicting strong first-order cosmological phase transitions in the early Universe.

820 citations


Journal ArticleDOI
TL;DR: In this paper, the authors exploit the unprecedented statistics provided by the Baryon Oscillation Spectroscopic Survey (BOSS) Data Release 9 to provide new constraints on the Hubble parameter H(z) using the cosmic chronometers approach.
Abstract: Deriving the expansion history of the Universe is a major goal of modern cosmology. To date, the most accurate measurements have been obtained with Type Ia Supernovae (SNe) and Baryon Acoustic Oscillations (BAO), providing evidence for the existence of a transition epoch at which the expansion rate changes from decelerated to accelerated. However, these results have been obtained within the framework of specific cosmological models that must be implicitly or explicitly assumed in the measurement. It is therefore crucial to obtain measurements of the accelerated expansion of the Universe independently of assumptions on cosmological models. Here we exploit the unprecedented statistics provided by the Baryon Oscillation Spectroscopic Survey (BOSS, [1-3]) Data Release 9 to provide new constraints on the Hubble parameter H(z) using the cosmic chronometers approach. We extract a sample of more than 130000 of the most massive and passively evolving galaxies, obtaining five new cosmology-independent H(z) measurements in the redshift range 0.3 < z < 0.5, with an accuracy of ~11–16% incorporating both statistical and systematic errors. Once combined, these measurements yield a 6% accuracy constraint of H(z = 0.4293) = 91.8 ± 5.3 km/s/Mpc. The new data are crucial to provide the first cosmology-independent determination of the transition redshift at high statistical significance, measuring zt = 0.4 ± 0.1, and to significantly disfavor the null hypothesis of no transition between decelerated and accelerated expansion at 99.9% confidence level. This analysis highlights the wide potential of the cosmic chronometers approach: it permits to derive constraints on the expansion history of the Universe with results competitive with standard probes, and most importantly, being the estimates independent of the cosmological model, it can constrain cosmologies beyond—and including—the ΛCDM model.

766 citations


Journal ArticleDOI
TL;DR: In this article, the authors exploit the unprecedented statistics provided by the Baryon Oscillation Spectroscopic Survey (BOSS) Data Release 9 to provide new constraints on the Hubble parameter using the em cosmic chronometers approach.
Abstract: Deriving the expansion history of the Universe is a major goal of modern cosmology. To date, the most accurate measurements have been obtained with Type Ia Supernovae and Baryon Acoustic Oscillations, providing evidence for the existence of a transition epoch at which the expansion rate changes from decelerated to accelerated. However, these results have been obtained within the framework of specific cosmological models that must be implicitly or explicitly assumed in the measurement. It is therefore crucial to obtain measurements of the accelerated expansion of the Universe independently of assumptions on cosmological models. Here we exploit the unprecedented statistics provided by the Baryon Oscillation Spectroscopic Survey (BOSS) Data Release 9 to provide new constraints on the Hubble parameter $H(z)$ using the em cosmic chronometers approach. We extract a sample of more than 130000 of the most massive and passively evolving galaxies, obtaining five new cosmology-independent $H(z)$ measurements in the redshift range $0.3

658 citations


Journal ArticleDOI
TL;DR: In this article, a comprehensive cosmological study of the H0 tension between the direct local measurement and the model-dependent value inferred from the Cosmic Microwave Background is performed.
Abstract: We perform a comprehensive cosmological study of the H0 tension between the direct local measurement and the model-dependent value inferred from the Cosmic Microwave Background. With the recent measurement of H0 this tension has raised to more than 3 σ. We consider changes in the early time physics without modifying the late time cosmology. We also reconstruct the late time expansion history in a model independent way with minimal assumptions using distance measurements from Baryon Acoustic Oscillations and Type Ia Supernovae, finding that at z < 0.6 the recovered shape of the expansion history is less than 5% different than that of a standard ΛCDM model. These probes also provide a model insensitive constraint on the low-redshift standard ruler, measuring directly the combination rsh where H0 = h × 100 Mpc−1km/s and rs is the sound horizon at radiation drag (the standard ruler), traditionally constrained by CMB observations. Thus rs and H0 provide absolute scales for distance measurements (anchors) at opposite ends of the observable Universe. We calibrate the cosmic distance ladder and obtain a model-independent determination of the standard ruler for acoustic scale, rs. The tension in H0 reflects a mismatch between our determination of rs and its standard, CMB-inferred value. Without including high-l Planck CMB polarization data (i.e., only considering the ``recommended baseline" low-l polarisation and temperature and the high l temperature data), a modification of the early-time physics to include a component of dark radiation with an effective number of species around 0.4 would reconcile the CMB-inferred constraints, and the local H0 and standard ruler determinations. The inclusion of the ``preliminary" high-l Planck CMB polarisation data disfavours this solution.

650 citations


01 Jan 2016
TL;DR: The gravitation and cosmology is universally compatible with any devices to read and is available in the book collection an online access to it is set as public so you can get it instantly.
Abstract: Thank you for downloading gravitation and cosmology. As you may know, people have search hundreds times for their chosen novels like this gravitation and cosmology, but end up in malicious downloads. Rather than reading a good book with a cup of coffee in the afternoon, instead they juggled with some malicious bugs inside their laptop. gravitation and cosmology is available in our book collection an online access to it is set as public so you can get it instantly. Our digital library spans in multiple locations, allowing you to get the most less latency time to download any of our books like this one. Merely said, the gravitation and cosmology is universally compatible with any devices to read.

576 citations


Journal ArticleDOI
TL;DR: A review of the progress in the construction of modified gravity models as alternatives to dark energy as well as the development of cosmological tests of gravity can be found in this paper.
Abstract: We review recent progress in the construction of modified gravity models as alternatives to dark energy as well as the development of cosmological tests of gravity. Einstein's theory of general relativity (GR) has been tested accurately within the local universe i.e. the Solar System, but this leaves the possibility open that it is not a good description of gravity at the largest scales in the Universe. This being said, the standard model of cosmology assumes GR on all scales. In 1998, astronomers made the surprising discovery that the expansion of the Universe is accelerating, not slowing down. This late-time acceleration of the Universe has become the most challenging problem in theoretical physics. Within the framework of GR, the acceleration would originate from an unknown dark energy. Alternatively, it could be that there is no dark energy and GR itself is in error on cosmological scales. In this review, we first give an overview of recent developments in modified gravity theories including f(R) gravity, braneworld gravity, Horndeski theory and massive/bigravity theory. We then focus on common properties these models share, such as screening mechanisms they use to evade the stringent Solar System tests. Once armed with a theoretical knowledge of modified gravity models, we move on to discuss how we can test modifications of gravity on cosmological scales. We present tests of gravity using linear cosmological perturbations and review the latest constraints on deviations from the standard [Formula: see text]CDM model. Since screening mechanisms leave distinct signatures in the non-linear structure formation, we also review novel astrophysical tests of gravity using clusters, dwarf galaxies and stars. The last decade has seen a number of new constraints placed on gravity from astrophysical to cosmological scales. Thanks to on-going and future surveys, cosmological tests of gravity will enjoy another, possibly even more, exciting ten years.

482 citations


Journal ArticleDOI
TL;DR: In this article, the authors identify a scalar-tensor model embedded in the Horndeski action whose cosmological background and linear scalar fluctuations are degenerate with the concordance cosmology.
Abstract: We identify a scalar-tensor model embedded in the Horndeski action whose cosmological background and linear scalar fluctuations are degenerate with the concordance cosmology. The model admits a self-accelerated background expansion at late times that is stable against perturbations with a sound speed attributed to the new field that is equal to the speed of light. While degenerate in scalar fluctuations, self-acceleration of the model implies a present cosmological tensor mode propagation at 95 % of the speed of light with a damping of the wave amplitude that is 5 % less efficient than in general relativity. We show that these discrepancies are endemic to self-accelerated Horndeski theories with degenerate large-scale structure and are tested with measurements of gravitational waves emitted by events at cosmological distances. Hence, gravitational-wave cosmology breaks the dark degeneracy in observations of the large-scale structure between two fundamentally different explanations of cosmic acceleration—a cosmological constant and a scalar-tensor modification of gravity. The gravitational wave event GW150914 recently detected with the aLIGO instruments and its potential association with a weak short gamma-ray burst observed with the Fermi GBM experiment may have provided this crucial measurement.

402 citations


Journal ArticleDOI
TL;DR: In this paper, a review of models in both categories as well as their phenomenology and characteristic observable signatures in cosmology is given. And a rigorous distinction between dark energy and modified gravity based on the strong and weak equivalence principles is introduced.
Abstract: Understanding the reason for the observed accelerated expansion of the Universe represents one of the fundamental open questions in physics. In cosmology, a classification has emerged among physical models for the acceleration, distinguishing between Dark Energy and Modified Gravity. In this review, we give a brief overview of models in both categories as well as their phenomenology and characteristic observable signatures in cosmology. We also introduce a rigorous distinction between Dark Energy and Modified Gravity based on the strong and weak equivalence principles.

369 citations


Journal ArticleDOI
TL;DR: In this paper, the authors provide a brief overview of models in both categories as well as their phenomenology and characteristic observable signatures in cosmology and introduce a rigorous distinction between dark energy and modified gravity based on the strong and weak equivalence principles.
Abstract: Understanding the reason for the observed accelerated expansion of the Universe represents one of the fundamental open questions in physics. In cosmology, a classification has emerged among physical models for this acceleration, distinguishing between dark energy and modified gravity. In this review, we provide a brief overview of models in both categories as well as their phenomenology and characteristic observable signatures in cosmology. We also introduce a rigorous distinction between dark energy and modified gravity based on the strong and weak equivalence principles.

277 citations


Journal ArticleDOI
TL;DR: In this paper, the search for the curl component (B mode) in the cosmic microwave background (CMB) polarization induced by inflationary gravitational waves is described, and issues involved in the experimental pursuit of these B modes are described.
Abstract: The search for the curl component (B mode) in the cosmic microwave background (CMB) polarization induced by inflationary gravitational waves is described. The canonical single-field slow-roll model of inflation is presented, and we explain the quantum production of primordial density perturbations and gravitational waves. It is shown how these gravitational waves then give rise to polarization in the CMB. We then describe the geometric decomposition of the CMB polarization pattern into a curl-free component (E mode) and curl component (B mode) and show explicitly that gravitational waves induce B modes. We discuss the B modes induced by gravitational lensing and by Galactic foregrounds and show how both are distinguished from those induced by inflationary gravitational waves. Issues involved in the experimental pursuit of these B modes are described, and we summarize some of the strategies being pursued. We close with a brief discussion of some other avenues toward detecting/characterizing the inflationar...

Journal ArticleDOI
T. M. C. Abbott, F. B. Abdalla, S. Allam, Adam Amara, J. Annis, Robert Armstrong, David Bacon, Manda Banerji, A. H. Bauer, Eric J. Baxter, Matthew R. Becker, A. Benoit-Lévy, Rebecca A. Bernstein, Gary Bernstein, E. Bertin, Jonathan Blazek, C. Bonnett, Sarah Bridle, David Brooks, Claudio Bruderer, E. Buckley-Geer, D. L. Burke, M. T. Busha, Diego Capozzi, A. Carnero Rosell, M. Carrasco Kind, J. Carretero, Francisco J. Castander, Chihway Chang, Joseph Clampitt, Martin Crocce, Carlos E. Cunha, C. B. D'Andrea, L. N. da Costa, R. Das, Darren L. DePoy, Shantanu Desai, H. T. Diehl, J. P. Dietrich, Scott Dodelson, P. Doel, Alex Drlica-Wagner, George Efstathiou, Tim Eifler, Brandon M. S. Erickson, Juan Estrada, August E. Evrard, A. Fausti Neto, Enrique J. Fernández, D. A. Finley, B. Flaugher, Pablo Fosalba, Oliver Friedrich1, Joshua A. Frieman, C. Gangkofner, Juan Garcia-Bellido, Enrique Gaztanaga, D. W. Gerdes, Daniel Gruen1, Robert A. Gruendl, G. Gutierrez, W. G. Hartley, Michael Hirsch, K. Honscheid, E. M. Huff, Bhuvnesh Jain, David J. James, Matt J. Jarvis, T. Kacprzak, Steve Kent, D. Kirk, Elisabeth Krause, Andrey V. Kravtsov, Kyler Kuehn, Nikolay Kuropatkin, J. Kwan, Ofer Lahav, Boris Leistedt, Tianjun Li, Marcos Lima, Huan Lin, N. MacCrann, M. March, Jennifer L. Marshall, P. Martini, Richard G. McMahon, Peter Melchior, C. J. Miller, Ramon Miquel, Joseph J. Mohr1, Eric H. Neilsen, Robert C. Nichol, Andrina Nicola, Brian Nord, Ricardo L. C. Ogando, Antonella Palmese, H. V. Peiris, A. A. Plazas, A. Refregier, Natalie A. Roe, A. K. Romer, A. Roodman, Barnaby Rowe, E. S. Rykoff, Cristiano G. Sabiu, I. Sadeh, M. Sako, S. Samuroff, E. J. Sanchez, Carles Sanchez, Hee-Jong Seo, I. Sevilla-Noarbe, Erin Sheldon, Robert Connon Smith, Marcelle Soares-Santos, Flavia Sobreira, E. Suchyta, M. E. C. Swanson, Gregory Tarle, J. J. Thaler, Daniel Thomas, Michael Troxel, Vinu Vikram, Alistair R. Walker, Risa H. Wechsler, Jochen Weller1, Yanxi Zhang, Joe Zuntz 
TL;DR: In this paper, the first constraints on cosmology from the Dark Energy Survey (DES), using weak lensing measurements from the preliminary Science Verification (SV) data, were presented.
Abstract: We present the first constraints on cosmology from the Dark Energy Survey (DES), using weak lensing measurements from the preliminary Science Verification (SV) data. We use 139 square degrees of SV data, which is less than 3% of the full DES survey area. Using cosmic shear 2-point measurements over three redshift bins we find sigma8(Omegam/0.3 )0.5=0.81 ±0.06 (68% confidence), after marginalizing over 7 systematics parameters and 3 other cosmological parameters. We examine the robustness of our results to the choice of data vector and systematics assumed, and find them to be stable. About 20% of our error bar comes from marginalizing over shear and photometric redshift calibration uncertainties. The current state-of-the-art cosmic shear measurements from CFHTLenS are mildly discrepant with the cosmological constraints from Planck CMB data; our results are consistent with both data sets. Our uncertainties are ˜30 % larger than those from CFHTLenS when we carry out a comparable analysis of the two data sets, which we attribute largely to the lower number density of our shear catalogue. We investigate constraints on dark energy and find that, with this small fraction of the full survey, the DES SV constraints make negligible impact on the Planck constraints. The moderate disagreement between the CFHTLenS and Planck values of sigma8(Omegam/0.3 )0.5 is present regardless of the value of w .

Proceedings ArticleDOI
TL;DR: The Hydrogen Intensity and Real-time Analysis eXperiment (HIRAX) is a new 400{800MHz radio interferometer under development for deployment in South Africa.
Abstract: The Hydrogen Intensity and Real-time Analysis eXperiment (HIRAX) is a new 400{800MHz radio interferometer under development for deployment in South Africa. HIRAX will comprise 1024 six meter parabolic dishes on a compact grid and will map most of the southern sky over the course of four years. HIRAX has two primary science goals: to constrain Dark Energy and measure structure at high redshift, and to study radio transients and pulsars. HIRAX will observe unresolved sources of neutral hydrogen via their redshifted 21-cm emission line (`hydrogen intensity mapping'). The resulting maps of large-scale structure at redshifts 0.8{2.5 will be used to measure Baryon Acoustic Oscillations (BAO). BAO are a preferential length scale in the matter distribution that can be used to characterize the expansion history of the Universe and thus understand the properties of Dark Energy. HIRAX will improve upon current BAO measurements from galaxy surveys by observing a larger cosmological volume (larger in both survey area and redshift range) and by measuring BAO at higher redshift when the expansion of the universe transitioned to Dark Energy domination. HIRAX will complement CHIME, a hydrogen intensity mapping experiment in the Northern Hemisphere, by completing the sky coverage in the same redshift range. HIRAX's location in the Southern Hemisphere also allows a variety of cross-correlation measurements with large-scale structure surveys at many wavelengths. Daily maps of a few thousand square degrees of the Southern Hemisphere, encompassing much of the Milky Way galaxy, will also open new opportunities for discovering and monitoring radio transients. The HIRAX correlator will have the ability to rapidly and efficiently detect transient events. This new data will shed light on the poorly understood nature of fast radio bursts (FRBs), enable pulsar monitoring to enhance long-wavelength gravitational wave searches, and provide a rich data set for new radio transient phenomena searches. This paper discusses the HIRAX instrument, science goals, and current status.© (2016) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

Journal ArticleDOI
TL;DR: In this paper, the authors analyse the dependence of the mass function on the way haloes are identified and establish if this can cause departures from universality, using a set of different N-body cosmological simulations (Le SBARBINE simulations).
Abstract: The abundance of galaxy clusters can constrain both the geometry and growth of structure in our Universe. However, this probe could be significantly complicated by recent claims of non-universality-non-trivial dependences with respect to the cosmological model and redshift. In this work, we analyse the dependence of the mass function on the way haloes are identified and establish if this can cause departures from universality. In order to explore this dependence, we use a set of different N-body cosmological simulations (Le SBARBINE simulations), with the latest cosmological parameters from the Planck collaboration; this first suite of simulations is followed by a lower resolution set, carried out with different cosmological parameters. We identify dark matter haloes using a spherical overdensity algorithm with varying overdensity thresholds (virial, 2000, 1000, 500, 200 rho(c) and 200 rho(b)) at all redshifts. We notice that, when expressed in terms of the rescaled variable., the mass function for virial haloes is a nearly universal as a function of redshift and cosmology, while this is clearly not the case for the other overdensities we considered. We provide fitting functions for the halo mass function parameters as a function of overdensity, that allow us to predict, to within a few per cent accuracy, the halo mass function for a wide range of halo definitions, redshifts and cosmological models. We then show how the departures from universality associated with other halo definitions can be derived by combining the universality of the virial definition with the expected shape of the density profile of haloes.

Journal ArticleDOI
TL;DR: When general relativity is included in large-scale simulations of the cosmic structure of the universe, relativistic effects turn out to be small but measurable, thus providing tests for models of dark matter and dark energy as mentioned in this paper.
Abstract: When general relativity is included in large-scale simulations of the cosmic structure of the Universe, relativistic effects turn out to be small but measurable, thus providing tests for models of dark matter and dark energy.

Journal ArticleDOI
T. Kacprzak1, Donnacha Kirk2, Oliver Friedrich3, Adam Amara1, Alexandre Refregier1, Laura Marian4, J. P. Dietrich5, E. Suchyta6, J. Aleksić7, David Bacon8, Matthew R. Becker9, C. Bonnett7, Sarah Bridle10, Chihway Chang1, Tim Eifler11, W. G. Hartley1, W. G. Hartley2, E. M. Huff12, Elisabeth Krause9, Niall MacCrann10, Peter Melchior13, Andrina Nicola1, S. Samuroff10, E. Sheldon14, Michael Troxel10, Jochen Weller3, Joe Zuntz10, T. M. C. Abbott, F. B. Abdalla15, F. B. Abdalla2, Robert Armstrong13, A. Benoit-Lévy2, A. Benoit-Lévy16, Gary Bernstein6, R. A. Bernstein17, E. Bertin16, David Brooks2, D. L. Burke9, D. L. Burke18, A. Carnero Rosell, M. Carrasco Kind19, M. Carrasco Kind20, J. Carretero21, J. Carretero9, Francisco J. Castander21, Martin Crocce21, C. B. D'Andrea7, C. B. D'Andrea22, L. N. da Costa, Shantanu Desai5, H. T. Diehl23, August E. Evrard24, A. Fausti Neto, B. Flaugher23, Pablo Fosalba21, Josh Frieman25, Josh Frieman23, D. W. Gerdes24, Daniel A. Goldstein26, Daniel A. Goldstein27, Daniel Gruen9, Daniel Gruen18, Robert A. Gruendl20, Robert A. Gruendl19, G. Gutierrez23, K. Honscheid12, Bhuvnesh Jain6, David J. James, M. Jarvis6, Kyler Kuehn28, Nikolay Kuropatkin23, Ofer Lahav2, Marcos Lima29, M. March6, Jennifer L. Marshall30, P. Martini12, C. J. Miller24, Ramon Miquel7, Ramon Miquel31, Joseph J. Mohr3, Robert C. Nichol8, Brian Nord23, A. A. Plazas11, A. K. Romer4, A. Roodman18, A. Roodman9, Eli S. Rykoff9, Eli S. Rykoff18, E. J. Sanchez32, V. Scarpine23, Michael Schubnell24, I. Sevilla-Noarbe32, R. C. Smith, Marcelle Soares-Santos23, Flavia Sobreira23, M. E. C. Swanson20, Gregory Tarle24, Daniel Thomas8, V. Vikram33, Alistair R. Walker, Yanming Zhang23 
TL;DR: In this paper, a shear peak statistics analysis of the Dark Energy Survey (DES) Science Verification (SV) data, using weak gravitational lensing measurements from a 139 deg² field, was performed.
Abstract: Shear peak statistics has gained a lot of attention recently as a practical alternative to the two-point statistics for constraining cosmological parameters. We perform a shear peak statistics analysis of the Dark Energy Survey (DES) Science Verification (SV) data, using weak gravitational lensing measurements from a 139 deg² field. We measure the abundance of peaks identified in aperture mass maps, as a function of their signal-to-noise ratio, in the signal-to-noise range 0 4 would require significant corrections, which is why we do not include them in our analysis. We compare our results to the cosmological constraints from the two-point analysis on the SV field and find them to be in good agreement in both the central value and its uncertainty. We discuss prospects for future peak statistics analysis with upcoming DES data.

Journal ArticleDOI
TL;DR: In this paper, the authors used the same method of analysis already adopted in the Euclid Red Book, which is based on the Fisher matrix approach, to forecast the constraints on cosmological parameters corresponding to different extensions of the standard I \textgreater cold dark matter model.
Abstract: We study the characteristics of the galaxy cluster samples expected from the European Space Agency's Euclid satellite and forecast constraints on parameters describing a variety of cosmological models. In this paper we use the same method of analysis already adopted in the Euclid Red Book, which is based on the Fisher matrix approach. Based on our analytical estimate of the cluster selection function in the photometric Euclid survey, we forecast the constraints on cosmological parameters corresponding to different extensions of the standard I \textgreater cold dark matter model. Using only Euclid clusters, we find that the amplitude of the matter power spectrum will be constrained to Delta sigma(8) = 0.0014 and the mass density parameter to Delta Omega(m) = 0.0011. The dynamical evolution of dark energy will be constrained to Delta w(0) = 0.03 and Delta w(a) = 0.2 with free curvature Omega(k), resulting in a (w(0), w(a)) figure of merit (FoM) of 291. In combination with Planck cosmic microwave background (CMB) constraints, the amplitude of primordial non-Gaussianity will be constrained to Delta f(NL) a parts per thousand integral 6.6 for the local shape scenario. The growth factor parameter gamma, which signals deviations from general relativity, will be constrained to Delta gamma = 0.02, and the neutrino density parameter to Delta Omega(nu) = 0.0013 (or Delta am(nu) = 0.01). Including the Planck CMB covariance matrix improves dark energy constraints to Delta w(0) = 0.02, Delta w(a) = 0.07, and a FoM = 802. Knowledge of the observable-cluster mass scaling relation is crucial to reach these accuracies. Imaging and spectroscopic capabilities of Euclid will enable internal mass calibration from weak lensing and the dynamics of cluster galaxies, supported by external cluster surveys.

Journal ArticleDOI
TL;DR: The evolution of the number density of galaxies in the universe, and thus also the total number of galaxies, is a fundamental question with implications for a host of astrophysical problems including galaxy evolution and cosmology as discussed by the authors.
Abstract: The evolution of the number density of galaxies in the universe, and thus also the total number of galaxies, is a fundamental question with implications for a host of astrophysical problems including galaxy evolution and cosmology. However there has never been a detailed study of this important measurement, nor a clear path to answer it. To address this we use observed galaxy stellar mass functions up to z _ 8 to determine how the number densities of galaxies changes as a function of time and mass limit. We show that the increase in the total number density of galaxies (_T), more massive than M∗ = 106 M⊙ , decreases as _T _ t−1, where t is the age of the universe. We further show that this evolution turns-over and rather increases with time at higher mass lower limits of M∗ > 107 M⊙ . By using the M∗ = 106 M⊙ lower limit we further show that the total number of galaxies in the universe up to z = 8 is 2.0+0.7 −0.6 × 1012 (two trillion), almost a factor of ten higher than would be seen in an all sky survey at Hubble Ultra-Deep Field depth. We discuss the implications for these results for galaxy evolution, as well as compare our results with the latest models of galaxy formation. These results also reveal that the cosmic background light in the optical and near-infrared likely arise from these unobserved faint galaxies. We also show how these results solve the question of why the sky at night is dark, otherwise known as Olbers’ paradox.

Journal ArticleDOI
TL;DR: The sensitivity of future cosmological observations to the couplings of axions to photons, gluons, and charged fermions to be demonstrated to demonstrate the constraints achievable from cosmology will surpass existing bounds from laboratory experiments and astrophysical observations by orders of magnitude.
Abstract: Future cosmic microwave background experiments have the potential to probe the density of relativistic species at the subpercent level. This sensitivity allows light thermal relics to be detected up to arbitrarily high decoupling temperatures. Conversely, the absence of a detection would require extra light species never to have been in equilibrium with the Standard Model. In this Letter, we exploit this feature to demonstrate the sensitivity of future cosmological observations to the couplings of axions to photons, gluons, and charged fermions. In many cases, the constraints achievable from cosmology will surpass existing bounds from laboratory experiments and astrophysical observations by orders of magnitude.

Journal ArticleDOI
TL;DR: In this article, the authors used the local value of the Hubble constant, as well as the latest compilation of cosmic chronometers data, together with standard probes such as Supernovae Type Ia and Baryon Acoustic Oscillation distance measurements, in order to impose constraints on the viable and most used f(T) gravity models, where T is the torsion scalar in teleparallel gravity.
Abstract: We use the local value of the Hubble constant recently measured with 2.4% precision, as well as the latest compilation of cosmic chronometers data, together with standard probes such as Supernovae Type Ia and Baryon Acoustic Oscillation distance measurements, in order to impose constraints on the viable and most used f(T) gravity models, where T is the torsion scalar in teleparallel gravity. In particular, we consider three f(T) models with two parameters, out of which one is independent, and we quantify their deviation from ΛCDM cosmology through a sole parameter. Our analysis reveals that for one of the models a small but non-zero deviation from ΛCDM cosmology is slightly favored, while for the other models the best fit is very close to ΛCDM scenario. Clearly, f(T) gravity is consistent with observations, and it can serve as a candidate for modified gravity.

Journal ArticleDOI
TL;DR: In this article, the authors review the main mechanisms of gravitational-wave production, ranging from quantum fluctuations of the gravitational field to other mechanisms that can take place during or after inflation, e.g. gravitational waves generated as a consequence of extra particle production during inflation, or during the (p)reheating phase.
Abstract: The production of a stochastic background of gravitational waves is a fundamental prediction of any cosmological inflationary model. The features of such a signal encode unique information about the physics of the Early Universe and beyond, thus representing an exciting, powerful window on the origin and evolution of the Universe. We review the main mechanisms of gravitational-wave production, ranging from quantum fluctuations of the gravitational field to other mechanisms that can take place during or after inflation. These include e.g. gravitational waves generated as a consequence of extra particle production during inflation, or during the (p)reheating phase. Gravitational waves produced in inflation scenarios based on modified gravity theories and second-order gravitational waves are also considered. For each analyzed case, the expected power spectrum is given. We discuss the discriminating power among different models, associated with the validity/violation of the standard consistency relation between tensor-to-scalar ratio r and tensor spectral index nT In light of the prospects for (directly/indirectly) detecting primordial gravitational waves, we give the expected present-day gravitational radiation spectral energy-density, highlighting the main characteristics imprinted by the cosmic thermal history, and we outline the signatures left by gravitational waves on the Cosmic Microwave Background and some imprints in the Large-Scale Structure of the Universe. Finally, current bounds and prospects of detection for inflationary gravitational waves are summarized.

Journal ArticleDOI
TL;DR: In this paper, the authors review the small-scale problems of the Lambda$CDM model and discuss the proposed solutions and to what extent they are able to give us a theory accurately describing the phenomena in the complete range of scale of the observed universe.
Abstract: The $\Lambda$CDM model, or concordance cosmology, as it is often called, is a paradigm at its maturity. It is clearly able to describe the universe at large scale, even if some issues remain open, such as the cosmological constant problem , the small-scale problems in galaxy formation, or the unexplained anomalies in the CMB. $\Lambda$CDM clearly shows difficulty at small scales, which could be related to our scant understanding, from the nature of dark matter to that of gravity; or to the role of baryon physics, which is not well understood and implemented in simulation codes or in semi-analytic models. At this stage, it is of fundamental importance to understand whether the problems encountered by the $\Lambda$DCM model are a sign of its limits or a sign of our failures in getting the finer details right. In the present paper, we will review the small-scale problems of the $\Lambda$CDM model, and we will discuss the proposed solutions and to what extent they are able to give us a theory accurately describing the phenomena in the complete range of scale of the observed universe.

Journal ArticleDOI
TL;DR: This analysis furnishes a powerful probe of deviations from Einstein's general relativity in the low-density regime which has largely remained untested so far and finds no evidence for such deviations in the data at hand.
Abstract: The Universe is mostly composed of large and relatively empty domains known as cosmic voids, whereas its matter content is predominantly distributed along their boundaries. The remaining material inside them, either dark or luminous matter, is attracted to these boundaries and causes voids to expand faster and to grow emptier over time. Using the distribution of galaxies centered on voids identified in the Sloan Digital Sky Survey and adopting minimal assumptions on the statistical motion of these galaxies, we constrain the average matter content Omega(m) = 0.281 +/- 0.031 in the Universe today, as well as the linear growth rate of structure f/b = 0.417 +/- 0.089 at median redshift (z) over bar = 0.57, where b is the galaxy bias (68% C.L.). These values originate from a percent-level measurement of the anisotropic distortion in the void-galaxy cross-correlation function, epsilon = 1.003 +/- 0.012, and are robust to consistency tests with bootstraps of the data and simulated mock catalogs within an additional systematic uncertainty of half that size. They surpass (and are complementary to) existing constraints by unlocking cosmological information on smaller scales through an accurate model of nonlinear clustering and dynamics in void environments. As such, our analysis furnishes a powerful probe of deviations from Einstein's general relativity in the low-density regime which has largely remained untested so far. We find no evidence for such deviations in the data at hand.

Journal ArticleDOI
TL;DR: In this article, the scaling relations of galaxy cluster X-ray luminosity, temperature and gas mass with mass and redshift, employing masses from robust weak gravitational lensing measurements, were investigated.
Abstract: We present constraints on the scaling relations of galaxy cluster X-ray luminosity, temperature and gas mass (and derived quantities) with mass and redshift, employing masses from robust weak gravitational lensing measurements. These are the first such results obtained from an analysis that simultaneously accounts for selection effects and the underlying mass function, and directly incorporates lensing data to constrain total masses. Our constraints on the scaling relations and their intrinsic scatters are in good agreement with previous studies, and reinforce a picture in which departures from self-similar scaling laws are primarily limited to cluster cores. However, the data are beginning to reveal new features that have implications for cluster astrophysics and provide new tests for hydrodynamical simulations. We find a positive correlation in the intrinsic scatters of luminosity and temperature at fixed mass, which is related to the dynamical state of the clusters. While the evolution of the nominal scaling relations over the redshift range $0.0

Journal ArticleDOI
TL;DR: In this article, a phenomenological non-gravitational coupling between dark energy and dark matter is investigated, where the interaction in the dark sector is parameterized as an energy transfer either from dark matter to dark energy or the opposite.
Abstract: We investigate a phenomenological non-gravitational coupling between dark energy and dark matter, where the interaction in the dark sector is parameterized as an energy transfer either from dark matter to dark energy or the opposite. The models are constrained by a whole host of updated cosmological data: cosmic microwave background temperature anisotropies and polarization, high-redshift supernovae, baryon acoustic oscillations, redshift space distortions and gravitational lensing. Both models are found to be compatible with all cosmological observables, but in the case where dark matter decays into dark energy, the tension with the independent determinations of H0 and σ8, already present for standard cosmology, increases: this model in fact predicts lower H0 and higher σ8, mostly as a consequence of the higher amount of dark matter at early times, leading to a stronger clustering during the evolution. Instead, when dark matter is fed by dark energy, the reconstructed values of H0 and σ8 nicely agree with their local determinations, with a full reconciliation between high- and low-redshift observations. A non-zero coupling between dark energy and dark matter, with an energy flow from the former to the latter, appears therefore to be in better agreement with cosmological data.

Journal ArticleDOI
TL;DR: Taking account of the empirical procedure by which corrections are made to their absolute magnitudes to allow for the varying shape of the light curve and extinction by dust, it is found that the data are still quite consistent with a constant rate of expansion.
Abstract: The ‘standard’ model of cosmology is founded on the basis that the expansion rate of the universe is accelerating at present — as was inferred originally from the Hubble diagram of Type Ia supernovae. There exists now a much bigger database of supernovae so we can perform rigorous statistical tests to check whether these ‘standardisable candles’ indeed indicate cosmic acceleration. Taking account of the empirical procedure by which corrections are made to their absolute magnitudes to allow for the varying shape of the light curve and extinction by dust, we find, rather surprisingly, that the data are still quite consistent with a constant rate of expansion.

Journal ArticleDOI
TL;DR: In this article, the early Universe production of sterile neutrino Dark Matter by the decays of singlet scalars is investigated. But the authors focus on how to incorporate bounds from structure formation on the level of the linear power spectrum, since the simplistic estimate using the free streaming horizon clearly fails for highly nonthermal distributions.
Abstract: We investigate the early Universe production of sterile neutrino Dark Matter by the decays of singlet scalars. All previous studies applied simplifying assumptions and/or studied the process only on the level of number densities, which makes it impossible to give statements about cosmic structure formation. We overcome these issues by dropping all simplifying assumptions (except for one we showed earlier to work perfectly) and by computing the full course of Dark Matter production on the level of non-thermal momentum distribution functions. We are thus in the position to study all aspects of the resulting settings and apply all relevant bounds in a reliable manner. We have a particular focus on how to incorporate bounds from structure formation on the level of the linear power spectrum, since the simplistic estimate using the free-streaming horizon clearly fails for highly non-thermal distributions. Our work comprises the most detailed and comprehensive study of sterile neutrino Dark Matter production by scalar decays presented so far.

Journal ArticleDOI
TL;DR: In this paper, the authors derived constraints on the spectrum of this gravitational radiation, and hence on theories of the early Universe, by combining experiments that cover 29 orders of magnitude in frequency, including Planck observations of cosmic microwave background temperature and polarization power spectra, together with baryon acoustic oscillations and big bang nucleosynthesis measurements, as well as new pulsar timing array and ground-based interferometer limits.
Abstract: Quantum fluctuations of the gravitational field in the early Universe, amplified by inflation, produce a primordial gravitational-wave background across a broad frequency band. We derive constraints on the spectrum of this gravitational radiation, and hence on theories of the early Universe, by combining experiments that cover 29 orders of magnitude in frequency. These include Planck observations of cosmic microwave background temperature and polarization power spectra and lensing, together with baryon acoustic oscillations and big bang nucleosynthesis measurements, as well as new pulsar timing array and ground-based interferometer limits. While individual experiments constrain the gravitational-wave energy density in specific frequency bands, the combination of experiments allows us to constrain cosmological parameters, including the inflationary spectral index n_t and the tensor-to-scalar ratio r. Results from individual experiments include the most stringent nanohertz limit of the primordial background to date from the Parkes Pulsar Timing Array, Ω_(GW)(f) < 2.3 × 10^(−10). Observations of the cosmic microwave background alone limit the gravitational-wave spectral index at 95% confidence to n_t ≲ 5 for a tensor-to-scalar ratio of r = 0.11. However, the combination of all the above experiments limits n_t < 0.36. Future Advanced LIGO observations are expected to further constrain n_t < 0.34 by 2020. When cosmic microwave background experiments detect a nonzero r, our results will imply even more stringent constraints on n_t and, hence, theories of the early Universe.

Journal ArticleDOI
TL;DR: In this article, the authors report on the first joint analysis of observational signatures from the electroweak baryogenesis in both gravitational wave (GW) detectors and particle colliders and find that it yields GW signals testable with the Evolved Laser Interferometer Space Antenna, Deci-hertz interferometer Gravitational Wave Observatory, and Big Bang Observer, and further identify collider signals from the same mechanism that are observable at the Circular Electron Positron Collider.
Abstract: We report on the first joint analysis of observational signatures from the electroweak baryogenesis in both gravitational wave (GW) detectors and particle colliders. With an effective extension of the Higgs sector in terms of the dimension-six operators, we derive a strong first-order phase transition associated with a sizable CP violation to realize a successful electroweak baryogenesis. We calculate the GW spectrum resulting from the bubble nucleation, plasma transportation, and magnetohydrodynamic turbulence of this process that occurred after the big bang and find that it yields GW signals testable with the Evolved Laser Interferometer Space Antenna, Deci-hertz Interferometer Gravitational Wave Observatory, and Big Bang Observer. We further identify collider signals from the same mechanism that are observable at the planning Circular Electron Positron Collider. Our analysis bridges astrophysics and cosmology with particle physics by providing significant motivation for searches for GW events peaking at the $(1{0}^{\ensuremath{-}4},1)\text{ }\mathrm{Hz}$ range, which are associated with signals at colliders, and highlights the possibility of an interdisciplinary observational window into baryogenesis. The technique applied in analyzing early Universe phase transitions may enlighten the study of phase transitions in applied science.

Journal ArticleDOI
TL;DR: In this article, the authors used the type Ia supernova luminosity distances to calibrate the correlation between the peak photon energy and the isotropic equivalent radiated energy in GRBs.
Abstract: Gamma-ray bursts are the most energetic explosions in the Universe. They are detectable up to very high redshifts, therefore can be used to study the expansion rate of the Universe and to investigate the observational properties of dark energy, provided that empirical correlations between spectral and intensity properties are appropriately calibrated. We used the type Ia supernova luminosity distances to calibrate the correlation between the peak photon energy, $E_{p, i}$, and the isotropic equivalent radiated energy, $ E_{iso}$ in GRBs. With this correlation, we tested the reliability of applying GRBs to measure cosmological parameters and to obtain indications on the basic properties and evolution of dark energy. Using 162 GRBs with measured redshifts and spectra, we applied a local regression technique to calibrate the $E_{p, i}$-$E_{iso}$ correlation against the type Ia SN data to build a calibrated GRB Hubble diagram. We tested the possible redshift dependence of the correlation and its effect on the Hubble diagram. Finally, we used the GRB Hubble diagram to investigate the dark energy EOS. For this, we focused on the so-called Chevalier-Polarski-Linder (CPL) parametrization of the dark energy EOS and implemented the Markov chain Monte Carlo (MCMC) method to efficiently sample the space of cosmological parameters. Our analysis shows once more that the $E_{p, i}$-$E_{iso}$ correlation has no significant redshift dependence. Therefore the high-redshift GRBs can be used as a cosmological tool to determine the basic cosmological parameters and to test different models of dark energy in the redshift region ($z\geqslant 3$), which is unexplored by the SNIa and baryonic acoustic oscillations data. Our updated calibrated Hubble diagram of GRBs provides some marginal indication (at $1\sigma$ level) of an evolving dark energy EOS.