Cannibalism's lingering imprint on the matter power spectrum

The early universe may have contained internally thermalized dark sectors that were decoupled from the Standard Model. In such scenarios, the relic dark thermal bath, composed of the lightest particle in the dark sector, can give rise to an epoch of early matter domination prior to Big Bang Nucleosynthesis, which has a potentially observable impact on the smallest dark matter structures. This lightest dark particle can easily and generically have number-changing self-interactions that give rise to “cannibal” behavior. We consider cosmologies where an initially sub-dominant cannibal species comes to temporarily drive the expansion of the universe, and we provide a simple map between the particle properties of the cannibal species and the key features of the enhanced dark matter perturbation growth in such cosmologies. We further demonstrate that cannibal self-interactions can determine the small-scale cutoff in the matter power spectrum even when the cannibal self-interactions freeze out prior to cannibal domination.

Singularities in Inflationary Cosmological Models

Due to the accelerated expansion of the universe, the possibilities for the formation of singularities has changed from the classical Big Bang and Big Crunch singularities to include a number of new scenarios. In recent papers it has been shown that such singularities may appear in inflationary cosmological models with a fractional power scalar field potential. In this paper we enlarge the analysis of singularities in scalar field cosmological models by the use of generalised power expansions of their Hubble scalars and their scalar fields in order to describe all possible models leading to a singularity, finding other possible cases. Unless a negative scalar field potential is considered, all singularities are weak and of type IV.

Scalarons mimicking dark matter in the Hu–Sawicki model of f(R ) gravity

In this paper, we conduct a study on the scalar field obtained from [Formula: see text] gravity via Weyl transformation of the spacetime metric [Formula: see text] from the Jordan frame to the Einstein frame. The scalar field is obtained as a result of the modification in the geometrical part of Einstein’s field equation of General Relativity. For the Hu–Sawicki model of [Formula: see text] gravity, we find the effective potential of the scalar field and calculate its mass. Our study shows that the scalar field (also named as scalaron) obtained from this model has the chameleonic property, i.e. the scalaron becomes light in the low-density region, while it becomes heavy in the high-density region of matter. Then it is found that the scalaron can be regarded as a dark matter (DM) candidate since the scalaron mass is found to be quite close to the mass of ultralight axions, a prime DM candidate. Thus, the scalaron in the Hu–Sawicki model of [Formula: see text] gravity behaves as DM. Further, a study on the evolution of the scalaron mass with the redshift is also carried out, which depicts that scalaron becomes light with expansion of the Universe and with different rates at different stages of the Universe.

A buyer’s guide to the Hubble constant

Since the expansion of the universe was first established by Edwin Hubble and Georges Lemaître about a century ago, the Hubble constant $$H_0$$ H 0 which measures its rate has been of great interest to astronomers. Besides being interesting in its own right, few properties of the universe can be deduced without it. In the last decade, a significant gap has emerged between different methods of measuring it, some anchored in the nearby universe, others at cosmological distances. The SH0ES team has found $$H_0 = 73.2 \pm 1.3 \; \;\,\hbox {kms}^{-1} \,\hbox {Mpc}^{-1}$$ H 0 = 73.2 ± 1.3 kms - 1 Mpc - 1 locally, whereas the value found for the early universe by the Planck Collaboration is $$H_0 = 67.4 \pm 0.5 \; \;\,\hbox {kms}^{-1} \,\hbox {Mpc}^{-1}$$ H 0 = 67.4 ± 0.5 kms - 1 Mpc - 1 from measurements of the cosmic microwave background. Is this gap a sign that the well-established $${\varLambda} {\text{CDM}}$$ Λ CDM cosmological model is somehow incomplete? Or are there unknown systematics? And more practically, how should humble astronomers pick between competing claims if they need to assume a value for a certain purpose? In this article, we review results and what changes to the cosmological model could be needed to accommodate them all. For astronomers in a hurry, we provide a buyer’s guide to the results, and make recommendations.

Phantom-like dark energy from quantum gravity

We analyse the emergent cosmological dynamics corresponding to the mean field hydrodynamics of quantum gravity condensates, in the group field theory formalism. We focus in particular on the cosmological effects of fundamental interactions, and on the contributions from different quantum geometric modes. The general consequence of such interactions is to produce an accelerated expansion of the universe, which can happen both at early times, after the quantum bounce predicted by the model, and at late times. Our main result is that, while this fails to give a compelling inflationary scenario in the early universe, it produces naturally a phantom-like dark energy dynamics at late times, compatible with cosmological observations. By recasting the emergent cosmological dynamics in terms of an effective equation of state, we show that it can generically cross the phantom divide, purely out of quantum gravity effects without the need of any additional phantom matter. Furthermore, we show that the dynamics avoids any Big Rip singularity, approaching instead a de Sitter universe asymptotically.

Post-Secular Identity? Developing a New Approach to Religion in International Relations and IR Studies

In spite of the increasing presence of religion in international relations with various publications observing this presence and numerous authorities calling for the inclusion of religion into mainstream research, there is no universal consent to recognize religion’s role in IR. In our opinion, the only way to reconcile IR with the international reality in which religion has been and will remain present in the foreseeable future is for the researchers themselves to construct—especially those oriented towards broad, non-Western perspective—a new face of the discipline, the face which in this article we call the post-secular identity of IR study. Assuming that identity is first and foremost a form of knowledge that tells us how we can define ourselves against the background of the surrounding world, our purpose is to look at the post-secular identity from two different perspectives which are analyzed in the two distinctive parts of the paper. On one hand, post-secular identity would mean the socio-political but also cultural phenomenon of the “knowledge of the self” expressed in the form of ideas, interests and goals of various state and nonstate actors, both religious and secular ones, that are more or less conditioned by religious determinants. We propose looking at them through the prism of a new kind of “partnership” emerging as a result of post-secular thinking in the area of IR. On the other hand, we want to look at post-secular identity as the badly required transformation within the area of IR study that, as we claim, needs to construct more inclusive views of IR scholars adopting a deliberative and pluralistic approach to the reality they examine based on widening their epistemological and hermeneutical horizons. This redefinition would be framed by recognizing religion as rational and adopting the view that the limits of the scientific methods do not coincide with the boundaries of rationality. We also adopt the view that along with the cognitive expansion of the universe, the concept of transcendence has been broadened.

R+RG gravity with maximal Noether symmetry

A Noether symmetric, 3rd order polynomial in the Riemann curvature tensor R αβμν extension of the General Relativity (GR) without cosmological constant (R+RG gravity) is suggested and discussed as a possible fundamental theory of gravity in 4-dimensional space-time with the geometric part of the Lagrangian to be L R + R G = − g 2 k R ( 1 + G G P ) . Here k = 8 π G N c 4 is the Einstein constant, g = det ( g μ ν ) , g μ ν - the metric tensor, GN - the Newton constant, c - the speed of light, R = R μ ν μ ν - the Ricci scalar, G = R 2 − 4 R μ ν R μ ν + R α β μ ν R α β μ ν - the Gauss-Bonnet topological invariant, and GP - a new constant of the gravitational self-interaction to model the cosmological bounce, inflation, accelerated expansion of the Universe, etc. The best fit to the Baryon Acoustic Oscillations data for the Hubble parameter H (z) at the redshifts z<2.36 leads to G P 1 / 4 = ( 0.557 ± 0.014 ) T p c − 1 with the mean square weighted deviation from the data about 3 times smaller than for the standard cosmological (ΛCDM) model. Due to the self-gravitating term ∼RG the respective Einstein equation in the R+RG gravity contains the additional (tachyonic in the past and now) scalar (spin = 0) graviton and the perfect geometric fluid tensor with pressure-and matter-like terms equal to the respective terms in the ΛCDM model at |z| 1. Some predictions of this R+RG gravity for the Universe are also done.

Noether symmetry approach in f (T, B) teleparallel gravity with a fermionic field

In this work, we consider a homogeneous and isotropic cosmological model of the universe in f (T, B) gravity with non-minimally coupled fermionic field. In order to find the form of the coupling function F(Ψ), the potential function V (Ψ) of the fermionic field and the function f (T, B), we found through the Noether symmetry approach. The results obtain are coincide with the observational data that describe the late-time accelerated expansion of the universe.