We generalize the standard model of particle physics such it displays global scale invariance. The gravitational action is also suitably modified such that it respects this symmetry. This model is interesting since the cosmological constant term is absent in the action. We find that the scale symmetry is broken by the recently introduced cosmological symmetry breaking mechanism. This simultaneously generates all the dimensionful parameters such as the Newton's gravitational constant, the particle masses and the vacuum or dark energy. We find that in its simplest version the model predicts the Higgs mass to be very small, which is ruled out experimentally. We further generalize the model such that it displays local scale invariance. In this case the Higgs particle disappears from the particle spectrum and instead we find a very massive vector boson. Hence the model gives a consistent description of particle physics phenomenology as well as fits the cosmological dark energy.
In this paper we consider the implications of a cosmological constant for the evolution of the universe, under a set of assumptions motivated by the holographic and horizon complementarity principles. We discuss the ``causal patch" description of spacetime required by this framework, and present some simple examples of cosmologies described this way. We argue that these assumptions inevitably lead to very deep paradoxes, which seem to require major revisions of our usual assumptions.
We discuss the possible cosmological implications of a class of superluminal particles, in a scenario where: a) Lorentz invariance is only an approximate property of the equations of a sector of matter; b) several critical speeds of matter in vacuum exist. The Big Bang scenario and the evolution of the very early universe, as well as large scale structure, can be strongly influenced by the new particles.
We discuss the cosmological implications of an antisymmetric tensor field when it experiences a kind of ``Higgs mechanism,'' including nonlocal interaction terms, on D-branes. Even when a huge magnetic-condensation-inducing anisotropy is assumed in the early universe, the expansion of the universe leads to an isotropic $B$-matter-dominated universe.
We investigate four-dimensional effective theories which are obtained by dimensional reduction of multidimensional cosmological models with factorizable geometry and consider the interaction between conformal excitations of the internal space (geometrical moduli excitations) and Abelian gauge fields. It is assumed that the internal space background can be stabilized by minima of an effective potential. The conformal excitations over such a background have the form of massive scalar fields (gravitational excitons) propagating in the external spacetime. We discuss cosmological and astrophysical …
We study the infrared effective theory of gravity that stems from the quantum trace anomaly. Quantum fluctuations of the metric induce running of the cosmological constant and the Newton constant at cosmological scales. By imposing the generalized Bianchi identity we obtain a prediction for the scale dependence of the dark matter and dark energy densities in terms of the parameters of the underlying conformal theory. For certain values of the model parameters the dark energy equation of state and the observed spectral index of the primordial density fluctuations can be simultaneously reproduce…
If Lorentz invariance is only an approximate property of equations describing a sector of matter above some critical distance scale, the speed of light c will not necessarily be the only critical speed in vacuum. Superluminal sectors of matter may exist related to new degrees of freedom not yet discovered experimentally. The new particles would not be tachyons: they may feel different minkowskian space-times with critical speeds much higher than c and behave kinematically like ordinary particles apart from the difference in critical speed. We present a discussion of possible physical (theoreti…
It is demonstrated that any realistic model of quintessence should be based on Supergravity since, when the scalar field is on tracks today, $Q\approx m_{\rm Pl}$. This improves the agreement between theoretical predictions and the current observations. In particular, a generic property is that ratio $ω_{\rm Q}\equiv p_{\rm Q}/ρ_{\rm Q}$ is pushed towards -1. A string-inspired model is proposed where the potential is given by $V(Q)= \frac{Λ^{4+α}}{Q^α}e^{\fracκ{2}Q^2}$. The model predicts $ω_{\rm Q}\approx -0.82$, a value less that one sigma from the current likehood value.
The lectures describe several cosmological effects produced by neutrinos. Upper and lower cosmological limits on neutrino mass are derived. The role that neutrinos may play in formation of large scale structure of the universe is described and neutrino mass limits are presented. Effects of neutrinos on cosmological background radiation and on big bang nucleosynthesis are discussed. Limits on the number of neutrino flavors and mass/mixing are given.
Astronomical observations are suggesting that the fine structure constant varies cosmologically. We present an analysis on the consequences that these variations might induce on the electromagnetic field as a whole. We show that under these circumstances the electrodynamics in vacuum could be described by two fields, the ``standard'' Maxwell's field and a new scalar field. We provide a generalised Lorentz force which can be used to test our results experimentally.
We study the generation of cosmological perturbations during the Hagedorn phase of string gas cosmology. Using tools of string thermodynamics we provide indications that it may be possible to obtain a nearly scale-invariant spectrum of cosmological fluctuations on scales which are of cosmological interest today. In our cosmological scenario, the early Hagedorn phase of string gas cosmology goes over smoothly into the radiation-dominated phase of standard cosmology, without having a period of cosmological inflation.
We consider some consequences of the presence of a cosmological lepton asymmetry in the form of neutrinos. Relic neutrino degeneracy enhances the contribution of massive neutrinos to the present energy density of the Universe, and modifies the power spectrum of radiation and matter. Comparing with current observations of cosmic microwave background anisotropies and large scale structure, we derive some constraints on the neutrino degeneracy and on the spectral index in the case of a flat Universe with a cosmological constant.
The upcoming Karlsruhe Tritium Neutrino (KATRIN) experiment will put unprecedented constraints on the absolute mass of the electron neutrino, $\mnue$. In this paper we investigate how this information on $\mnue$ will affect our constraints on cosmological parameters. We consider two scenarios; one where $\mnue=0$ (i.e., no detection by KATRIN), and one where $\mnue=0.3$eV. We find that the constraints on $\mnue$ from KATRIN will affect estimates of some important cosmological parameters significantly. For example, the significance of $n_s<1$ and the inferred value of $Ω_Λ$ depend on the result…
We discuss some cosmological implications of extensions of the Standard Model with hidden sector scalars coupled to the Higgs boson. We put special emphasis on the conformal case, in which the electroweak symmetry is broken radiatively with a Higgs mass above the experimental limit. Our refined analysis of the electroweak phase transition in this kind of models strengthens the prediction of a strongly first-order phase transition as required by electroweak baryogenesis. We further study gravitational wave production and the possibility of low-scale inflation as well as a viable dark matter can…
The non--linear dynamics of cosmological perturbations of an irrotational collisionless fluid is analyzed within General Relativity. Relativistic and Newtonian solutions are compared, stressing the different role of boundary conditions in the two theories. Cosmological implications of relativistic effects, already present at second order in perturbation theory, are studied and the dynamical role of the magnetic part of the Weyl tensor is elucidated.
We have investigated the cosmological implications of the bulk viscous cosmological model with variable G and $Λ$. These results are found to be compatible with the present observations. The classical cosmological tests for this model encompass the Freese et al ones. The model has some sprits of the Standard Model. The inflationary solution which solves the Standard Model problems is obtained as a special solution. The influence of viscosity is shown to affect the past and the future of the Universe.
The massive neutrinos gravitational infall and their inprints left on the CMB temperature and matter density fluctuations power spectra are analysed taking into account the massive neutrino properties: the mass degeneracy, the phase space mixing, the lepton asymmetry.
Cosmological implications of clusters of galaxies are discussed with particular attention to their importance in probing the cosmological parameters. More specifically we compute the number counts of clusters of galaxies, Log $N$ -- Log $S$ relation, in X-ray and submm bands on the basis of the Press--Schechter theory. We pay particular attention to a set of theoretical models which well reproduce the {\it ROSAT} 0.5-2 keV band Log $N$ -- Log $S$, and explore possibilities to break the degeneracy among the viable cosmological models.
We show that stable local cosmic strings are a generic prediction of supersymmetric models where supersymmetry is broken at scales within a few orders of magnitude of the weak scale and is fed down to the observable sector by gauge interactions. The typical energy scale of these strings is about $10^2$ TeV. Since in the most general and natural scenario there are two different sources of contributions to ordinary superpartner masses, gauge mediation from the messanger sector and anomalous U(1) D-terms, novel features are that the cosmic strings may be superconducting with the role of bosonic c…
We assume the validity of the Standard Model up to an arbitrary high-energy scale and discuss what information on the early stages of the Universe can be extracted from a measurement of the Higgs mass. For Mh < 130 GeV, the Higgs potential can develop an instability at large field values. From the absence of excessive thermal Higgs field fluctuations we derive a bound on the reheat temperature after inflation as a function of the Higgs and top masses. Then we discuss the interplay between the quantum Higgs fluctuations generated during the primordial stage of inflation and the cosmological per…
It has been argued that the spacetime of our universe can be accurately described by a perturbed conformal Newtonian metric, and hence even large density inhomogeneities in a dust universe can not change the observables predicted by the homogeneous dust model. In this paper we study a spherically symmetric dust model and illustrate conditions under which large spatial variations in the expansion rate can invalidate the argument.
In this paper we examine the cosmological constraints of the recent DIRBE and FIRAS detection of the extragalactic background light between 125-5000 microns on the metal and star formation histories of the universe.
We investigate gauge invariant cosmological perturbations in a spatially flat Friedman-Robertson-Walker universe with scalar fields. It is well known that the evolution equation for the gauge invariant quantities has exact solutions in the long-wavelength limit. We find that these gauge invariant solutions can be obtained by differentiating the background solution with respect to parameters contained in the background system. This method is very useful when we analyze the long-wavelength behavior of cosmological perturbation with multiple scalar fields.
The amplification of the protogalaxy candidate cB58 due to gravitational lensing by the foreground cluster of galaxies MS1512.4+3647 is quantified based on recent ROSAT and ASCA X-ray observations. It is found that the amplification is at most 25 for any reasonable cosmological model with or without cosmological constant. It is also argued that the system may be used to place new constraints on the value of the cosmological constant. The gas mass fraction for this cluster is found to be about 0.2.
I review the assumptions and observations that motivate the concept of the extragalactic cosmic background radiation, and the issues of energy accounts and star formation history as a function of galaxy morphological type that figure in the interpretation of the measurements of the extragalactic infrared background.
We show how gauge-invariant cosmological perturbations may be constructed by an unambiguous choice of hypersurface-orthogonal time-like vector field (i.e., time-slicing). This may be defined either in terms of the metric quantities such as curvature or shear, or using some matter field. As an example, we show how linear perturbations in the covariant fluid-flow approach can then be presented in an explicitly gauge-invariant form in the coordinate based formalism.
We describe the results of a hybrid matrix--Monte Carlo calculation of cascading of UHE cosmic rays and $γ$-rays through the cosmic background radiation fields over cosmological distances. We calculate the $γ$-ray and neutrino emission that results from the cascade, as well as the effect of cascading on the primary spectrum. We discuss the results for various cosmic ray injection spectra and primary species. Certain models for the production of the highest energy cosmic rays are ruled out.
Cosmological implications of clusters of galaxies are discussed with particular attention to their importance in probing the cosmological parameters. More specifically we compute the number counts of clusters of galaxies, Log $N$ -- Log $S$ relation, in X-ray and submm bands on the basis of the Press--Schechter theory. As an important step toward breaking the degeneracy among the viable cosmological models, we observed the most luminous X-ray cluster RXJ1347-1145 in three bands (21 and 43 GHz in the Nobeyama Radio Observatory, Japan, and 350 GHz in the J. C. Maxwell telescope at Mauna Kea, Haw…
We study the quark-hadron phase transition within an effective model of QCD, and find that in a reasonable range of the main parameters of the model, bodies with quark content between $10^{-2}$ and 10 solar masses can have been formed in the early universe. In addition, we show that a significant amount of entropy is released during the transition. This may imply the existence of a higher baryon number density than what is usually expected at temperatures above the QCD scale. The cosmological QCD transition may then provide a natural way for decreasing the high baryon asymmetry created by an A…
We investigate a model where neutrinos are strongly coupled to a new, light scalar field. In this model neutrinos annihilate as soon as they become non-relativistic in the early universe, and a non-zero neutrino mass has a marginal effect on the matter power spectrum. However, the angular power spectrum of the cosmic microwave background (CMB) is changed significantly because the strongly interacting fluid of neutrinos and scalars does not experience any anisotropic stress. Such models are strongly disfavoured by current observations. Interestingly, this leads to the conclusion that the relati…
Based on the two-parameter family nature of X-ray clusters of galaxies obtained in a separate paper, we discuss the formation history of clusters and cosmological parameters of the universe. Utilizing the spherical collapse model of cluster formation, and assuming that the cluster X-ray core radius is proportional to the virial radius at the time of the cluster collapse, the observed relations among the density, radius, and temperature of clusters imply that cluster formation occurs in a wide range of redshift. The observed relations favor the low-density universe. Moreover, we find that the m…
We examine the effects of the linear and the cosmological redshift-space distortions on the power spectrum of cosmological objects on a light cone. We develop theoretical formulae for the power spectrum in linear theory of density perturbations in a rigorous manner starting from first principle corresponding to Fourier analysis. Approximate formulae, which are useful properly to incorporate the redshift-space distortion effects into the power spectrum are derived, and the validity is examined. Applying our formulae to galaxy and quasar samples which roughly match the SDSS survey, we will show …
The galaxy cluster power spectrum and mass/temperature functions are currently the most precise observational tools for constraining the theory of the formation of large scale structure (LSS) in the Universe. Complementing these tests by the observational data at larger (cosmic microwave backgroud anisortopy (CMBA)) and smaller (distribution of $Ly_α$ clouds) scales opens the way to a straightforward determination of the cosmological parameters in simplest dark matter (DM) models. We argue that such a 'minimal data set' is free from systematic effects and can indicate quite precisely the param…
Non-minimal actions with matter represented by a scalar field coupled to gravity are considered in the context of a homogeneous and isotropic universe. The coupling is of the form $-ξ/2 ϕ^2 R$. The possibility of successful inflation is investigated taking into account features of loop cosmology. For that end a conformal transformation is performed. That brings the theory into the standard minimally coupled form (Einstein frame) with some effective field and its potential. Both analytical and numerical estimates show that a negative coupling constant is preferable for successful inflation. Mor…
The renormalization-group equation for the zero-point energies associated with vacuum fluctuations of massive fields from the Standard Model is examined. Our main observation is that at any scale the running is necessarily dominated by the heaviest degrees of freedom, in clear contradistinction with the Appelquist & Carazzone decoupling theorem. Such an enhanced running would represent a disaster for cosmology, unless a fine-tuned relation among the masses of heavy particles is imposed. In this way, we obtain $m_H \simeq 550 GeV$ for the Higgs mass, a value safely within the unitarity bound, b…
We review the findings for the values of the cosmological parameters as derived from high-redshift SNIa measurements. The most recent results confirm the picture of a non-empty inflationary Universe that is consistent with a cosmological constant Omega_Lambda~0.7. This implies that the expansion of the Universe is currently accelerated by the action of some mysterious dark energy. We also discuss the possibility and the consequences of the fact that SNIa may not be "perfect" standard candles, in the sense of having properties in the early Universe that are systematically different from those t…
Working within the framework of the minimal supergravity model with gauge coupling unification and radiative electroweak symmetry breaking, we evaluate the cosmological relic density from lightest neutralinos produced in the early universe. Our numerical calculation is distinct in that it involves direct evaluation of neutralino annihilation cross sections using helicity amplitude techniques, and thus avoids the usual expansion as a power series in terms of neutralino velocity. Thus, our calculation includes relativistic Boltzmann averaging, neutralino annihilation threshold effects, and prope…
Observations of the cosmic microwave background represent a remarkable source of information for modern cosmology. Besides providing impressive support for the Big Bang model itself, they quantify the overall framework, or background, for the formation of large scale structure. Most exciting, however, is the potential access these observations give to the first moments of cosmic history and to the physics reigning at such exceptionally high energies, which will remain beyond the reach of the laboratory in any foreseeable future. Upcoming experiments, such as the Planck mission, thus offer a wi…
Free electrons deplete photons from type Ia supernovae through the (inverse) Compton scattering. This Compton dimming increases with redshift and reaches 0.004 mag at $z=1$ and 0.01 mag at $z=2$. Although far from sufficient to invalidate the existence of dark energy, it can bias constraint on dark energy at a level non-negligible for future supernova surveys. This effect is correctable and should be incorporated in supernova analysis. The Compton dimming has similar impact on cosmology based on gamma ray bursts as standard candles.
The evolution of the temperature distribution function (TDF) of X-ray clusters is kn own to be a powerful cosmological test of the density parameter of the Universe. Recent XMM observations allows us to measure accurately the L - T relation of high redshift X-ray clusters. In order to investigate cosmological implication of this recent results, we have derived theoretical number counts for different X-ray clusters samp les, namely the RDCS, EMSS, SHARC, 160 deg^2 and MACS at z > 0.3 in different fl at models. We show that a standard hierarchical modeling of cluster distribution in a flat low d…
Cosmological implications of the observed large-scale peculiar velocities are reviewed, alone or combined with redshift surveys and CMB data. The latest version of the POTENT method for reconstructing the underlying three-dimensional velocity and mass-density fields is described. The initial fluctuations and the nature of the dark matter are addressed via statistics such as bulk flow and mass power spectrum. The focus is on constraining the mass density parameter $Ω$, directly or via the parameter $β$ which involves the unknown relation between galaxies and mass. The acceptable range for $Ω$ i…
We study the possibility of correctly identifying superclusters, from the smooth galaxy density field of the PSCz redshift catalogue, and of recovering their true shapes in the presence of a bias introduced by the coupling between the selection function and the constant radius smoothing. Using simulations we quantify such systematic biases in the smoothed PSCz density field and after applying the necessary corrections we study the PSCz supercluster multiplicity and morphologies using a differential geometry definition of shape. Our results strongly suggest that filamentariness is the dominant …
The discovery that the bolometric energetics (and/or peak luminosity) of Gamma Ray Bursts correlates with their spectral properties has allowed to standardize the burst energetics to such a degree to enable their use for constraining the cosmological parameters, in the same way as SN Ia. With respect to SN Ia, there is the advantage of having sources free from extinction problems, and easily detectable also at large redshifts. On the other hand, these spectral-energy correlations are not yet understood, and bursts with a complete set of information (to standardize their energetics) are still f…
We performed a systematic and comprehensive estimate of the Hubble constant $H_0$ via the Sunyaev-Zel'dovich temperature decrement and the X-ray measurements for clusters up to the redshift $z=0.541$, with particular attention to its dependence on the density parameter $Ω_0$, and the cosmological constant $λ_0$. The resulting values of $H_0$ are largely consistent with that derived from the Cepheid distance for nearby galaxies. We discuss how the angular diameter distance $d_A$ vs. $z$ diagram from the accurate SZ measurements of high-$z$ clusters can distinguish the values of $Ω_0$ and $λ_0$.
We report near simultaneous multi-color (RIYJHK) observations made with the MAGNUM 2m telescope of the gamma ray burst GRB 050904 detected by the SWIFT satellite. The spectral energy distribution shows a very large break between the I and J bands. Using intergalactic transmissions measured from high redshift quasars we show that the observations place a 95% confidence lower limit of z=6.18 on the object, consistent with a later measured spectroscopic redshift of 6.29 obtained by Kawai et al. (2005) with the Subaru telescope. We show that the break strength in the R and I bands is consistent wi…
Observations of stellar CNO isotope ratios indicate the presence of additional mixing processes on the red giant branch. An estimate of the resulting stellar He-3 depletion is made, as a function of stellar mass and metallicity. Based on stellar nucleosynthesis and galactic chemical evolution calculations, we determine the degree to which the destruction of He-3 due to such extra mixing processes can influence the inferred primordial abundance of ( D + He-3 ). We find that the extra mixing processes may increase the upper limit of the inferred primordial ( D + He-3 ) / H ratio by about 20%. Th…
In primordial gas, molecular hydrogen forms primarily through associative detachment of H- and H, thereby destroying the H-. The H- anion can also be destroyed by a number of other reactions, most notably by mutual neutralization with protons. However, neither the associative detachment nor the mutual neutralization rate coefficients are well determined: both may be uncertain by as much as an order of magnitude. This introduces a corresponding uncertainty into the H2 formation rate, which may have cosmological implications. Here, we examine the effect that these uncertainties have on the forma…
We have derived the invariants of cosmological models with Gurzadyan-Xue dark energy, along with the solutions for any time dependent light speed and gravitational constant. The correspondence of the invariants with the separatrices found earlier for the GX-models in \cite{Ver06a} is shown, and hence the basis of then detected hidden symmetry is now revealed. Solutions are derived both for radiation and matter models, as well as with both components. It is interesting that, the solutions for the scale factor do not depend on the gravitational constant but only on the 'time evolution' of the sp…
I review recent results of the high-redshift X-ray selected AGN clustering, based on the XMM/2dF survey. Using the luminosity-dependent density evolution luminosity function we find that the spatial clustering lengths, derived using Limber's inversion equation, are ~16 and ~19 h-1 Mpc respectively (for the comoving clustering evolution model) while the median redshifts of the soft and hard X-ray sources are z~ 1.2 and 0.75, respectively. Within the framework of flat cosmological models we find that these results support a model with Omega_m=0.26, σ_8=0.75, w=-0.9 (in excellent agreement with t…
We present a global measurement of the integrated Sachs-Wolfe (ISW) effect obtained by cross-correlating all relevant large scale galaxy data sets with the cosmic microwave background radiation map provided by the Wilkinson Microwave Anisotropy Probe. With these measurements, the overall ISW signal is detected at the ~ 4.5 sigma level. We also examine the cosmological implications of these measurements, particularly the dark energy equation of state w, its sound speed, and the overall curvature of the Universe. The flat LCDM model is a good fit to the data and, assuming this model, we find tha…
Using the covariant approach and conformal transformations, we present a gauge-invariant formalism for cosmological perturbations in generalized Einstein theories (GETs), including the Brans-Dicke theory, theories with a non-minimally coupled scalar field and certain curvature-squared theories. We find an enhancement in the growth rate of density perturbations in the Brans-Dicke theory, and discuss attractive features of GETs in the structure formation process.
Bearing on the model for the time-dependent metagalactic radiation field developed in the first paper of this series, we compute the gamma-ray attenuation due to pair production in photon-photon scattering. Emphasis is on the effects of varying the star formation rate and the fraction of UV radiation assumed to escape from the star forming regions, the latter being important mainly for high-redshift sources. Conversely, we investigate how the metagalactic radiation field can be measured from the gamma-ray pair creation cutoff as a function of redshift, the Fazio-Stecker relation. For three obs…
The observation by the BATSE instrument on the Compton Gamma Ray Observatory that gamma-ray bursts (GRBs) are distributed isotropically around the Earth but nonuniformly in distance has led to the widespread conclusion that GRBs are most likely to be at cosmological distances, making them the most luminous sources known in the Universe. If bursts arise from events that occur in normal galaxies, such as neutron star binary inspirals, then they will also occur in our Galaxy about every hundred thousand to million years. The gamma-ray flux at the Earth due to a Galactic GRB would far exceed that …
