Cosmological Implications Research Articles

Dynamical study of NTADE and SMHDE models within Rastall gravity

This paper is mainly focused to investigate the cosmological implications of Rastall gravity with the help of two dark energy models, i.e., new Tsallis agegraphic dark energy (NTADE) and Sharma-Mittal holographic dark energy (SMHDE). The background of flat FLRW space–time is being considered to develop the dynamical system of equations. To check the viability of these models and to distinguish them, we develop some important cosmological parameters. By constraining the involved model parameters, it is observed that the equation of state (EoS) parameter for the NTADE model lies in the phantom region whereas, for SMHDE, it shows quintom as well as quintessence regions depending on the values of model parameter δ . The deceleration parameter shows the phase transition from decelerating to the accelerating phase for both models. The ω D − ω D ′ pair shows freezing and thawing regions for NTADE, and the freezing region for SMHDE. The pair ( j , s ) for SMHDE indicates a rich behavior as it shows different DE eras, a phantom, the quintessence as well as Chaplygin gas but the NTADE model shows Chaplygin gas behavior only. We conclude that SMHDE is a more efficient model than the NTADE model because it approaches Λ CDM limit and the results for this model lie in a stable region as shown by graphical analysis of the square speed of sound. • This paper investigates the cosmological implications of Rastall gravity via two dark energy models, new Tsallis agegraphic dark energy (NTADE) and Sharma–Mittal holographic dark energy (SMHDE). • The background of flat FLRW space-time is being considered to develop the dynamical system of equations. To check these models’ viability and distinguish them, we develop some important cosmological parameters. • It is observed that the equation of state parameter for the NTADE model lies in the phantom region whereas, for SMHDE, it shows quintom as well as quintessence regions depending on the values of model parameter δ . • The deceleration parameter shows the phase transition from decelerating to accelerating one. • The ω D – ω D ′ pair shows freezing and thawing regions for NTADE and the freezing region for SMHDE. • The (j,s) pair for SMHDE indicates different DE eras; phantom, quintessence, and Chaplygin gas but for the NTADE model, it shows Chaplygin gas behavior only. • We concluded that SMHDE is an efficient model than the NTADE model as Λ CDM limit is approachable in this case and its results found to be stable region.

Cosmological implications of Born–Infeld-f(R) gravity

In this paper, a modified Born–Infeld gravitation theory with an [Formula: see text] function being added to the determinant action is analyzed from a cosmological viewpoint. The corresponding accelerating dynamics are studied in a simplified conformal approach without matter. Three different structures for the auxiliary metric function are analyzed, with the aim to establish a deeper understanding of the role of this function in cosmology. After performing the analysis, it is seen that by modifying the auxiliary metric function, a Big Rip singularity or either a Little Rip dark energy model may arise.

The Concept of Zhonghua in Modern Chinese Philosophy and its Cosmological Implications

The Concept of Zhonghua in Modern Chinese Philosophy and its Cosmological Implications

Gravity of Negative Mass: Some Subtle Aspects and Implications

The gravitational interaction has mass of only one sign as the source that is conventionally taken to be positive. The existence of negative mass is not precluded in either Newtonian gravity or general relativity. Negative masses have been invoked in many recent papers to understand the dominance of repulsive dark energy that is accelerating the universe. Here we discuss the various gravitating properties of negative mass particles and their implications for black holes, cosmology, and fundamental physics. Inconsistencies in the earlier works are also discussed. We study the possibility of such negative mass particles accounting for the accelerated expansion of the universe. We set constraints on the density of these negative mass particles based on astrophysical observations.

Meridian Circle Astrometry at the U. S. Naval Observatory

For 150 years meridian circles have played an essential part in the mission of the U. S. Naval Observatory (USNO) in its dual role as a naval observatory, in support of celestial navigation, and as a national observatory, improving the celestial reference frame of fundamental astronomy. Examining two 20th century USNO instruments, we depict meridian circles as multiple ensembles: of sets of supporting devices, of calibrations and reductions for precision, of collected observations forming catalogues of stars, and of multiple meridian circles cooperating to solve astronomical goals and to map the heavens from pole to pole. We end briefly summarizing the contributions of the USNO meridian circles in the satellite era, with some implications for astrophysics and cosmology.

Miracle as a Message: Cosmological, Anthropological and Educational Implications

The purpose of this article is to explain in religious, secular, and post-secular contexts the functional potential of conceptualizing the miracle as a text or message with a motivational effect. Theoretical basis. Max Weber, Ernst Tugendhat, Alexander Geppert and Till Kössler analysed the processes of enchantment and disenchantment of the world on a philosophical basis. The representatives of the Frankfurt school (Theodor Adorno, Max Horkheimer, Walter Benjamin) and their followers describe the cultural processes of post-secularism (Jürgen Habermas, Peter Sloterdijk) in detail. The logic of cultural and social representation of amazing events and their descriptions can be realized by combining hermeneutic analysis with a functionalist approach based on the model of Niklas Luhmann and the discursive ethics of Karl-Otto Apel. Originality. Desired cultural, social and political situations in society often arise unexpectedly and suddenly, which provokes to characterize them as a miracle. However, at the basis of the emergence of such situations are the rules of social communication, in particular those that provide for asymmetric communication with questions that await answers. A miracle appears at the moment of transformation of asymmetric communication into a symmetrical one: each specific miracle-phenomenon needs its own metaphorical understanding and interpretation as a message. Conclusions. The article proposes an analysis of miracle phenomenon in its cosmological, anthropological and educational implications. Some tendencies fixed by communicative turn of the contemporary philosophy are also contributed to considering the miracle in its objective and subjective representations. The semantics of the miracle is analysed according to the relevant problem fields. The functionality of miracle is examined on its ability to show orientation for the contemporary societies with their tendency to post-secularity. The fusion of Pre-modernity and Late Modernity is taking into account when the semantics of miracle is described accordingly to their communication functionality. The enchanting and disenchanting dialectic is explained on semantics of miracle as a world and cosmic events.

Glueball Dark Matter Revisited.

We revisit the possibility that dark matter is composed of stable scalar glueballs of a confining dark SU(3) gauge theory coupled only to gravity. The relic abundance of dark glueballs is studied for the first time in a thermal effective theory accounting for strong-coupling dynamics. An important ingredient of our analysis is the use of an effective potential for glueballs that is fitted by lattice simulations. We predict the relic abundance to be in the range 0.12ζ_{T}^{-3}Λ/(137.9 eV)≲Ωh^{2}≲0.12ζ_{T}^{-3}Λ/(82.7 eV), with Λ being the confinement scale, ζ_{T} the visible-to-dark sector temperature ratio, and the uncertainty is coming from the fit to lattice data. This prediction is an order of magnitude smaller than the existing glueball abundance results in the literature. Our framework can be easily generalized to different gauge groups and modified cosmological histories paving the way toward consistent exploration of strongly coupled dark sectors and their cosmological implications.

Cosmological aspects of anisotropic chameleonic Brans–Dicke gravity

We study the cosmological implications of non-minimal coupling of a scalar field with matter sector in the Brans–Dicke gravity. In particular, in the context of locally rotationally symmetric Bianchi-I (LRS BI) metric, we derived the field equations and used these equations to find a relation between scale factor and scalar field. We use this relation to find two different solutions, namely an eternally accelerating universe and a transit universe. By the power-law solutions for scalar field and coupling function, we find the allowed range of exponents for an accelerating universe. We further explore the direction and magnitude of energy transfer between scalar field and matter sector. We show by using the second law of thermodynamics that the direction and magnitude of energy transfer are closely related to the behavior of coupling function. In the transit universe, we investigate the dependence of the effective equation of state parameter and the effective energy density on the anisotropy parameter. The model explains the late-time accelerating universe evolution.

Type II Dirac seesaw portal to the mirror sector: Connecting neutrino masses and a solution to the strong CP problem

We present a version of the Type II seesaw mechanism for parametrically small Dirac neutrino masses. Our model starts from an $\mathrm{SU}(2{)}_{\mathrm{L}}\ensuremath{\bigotimes}\mathrm{SU}(2{)}^{\ensuremath{'}}\ensuremath{\bigotimes}\mathrm{U}(1{)}_{\mathrm{X}}$ gauge extension of the Standard Model involving a sector of mirror fermions. A bidoublet scalar with a very small vacuum expectation value connects the SM leptons with their mirror counterparts, and we can identify the mirror neutrino with the right-handed neutrino. Similar to the conventional Type II seesaw, our particle spectrum features singly and doubly charged scalars. The strong $CP$ problem is solved by a discrete exchange symmetry between the two sectors that forces the contributions of quarks and mirror quarks to the strong $CP$ phase to cancel each other. We discuss the low-energy phenomenology, comment on the cosmological implications of this scenario, and indicate how to realize successful Dirac leptogenesis.

Squared Torsion f(T,T)$f(T,\mathcal {T})$ Gravity and Its Cosmological Implications

AbstractWe present the coupling of the torsion scalar T and the trace of energy‐momentum tensor , which produces new modified gravity. Moreover, we consider the functional form where α and β are free parameters. As an alternative to a cosmological constant, the theory may offer a theoretical explanation of the late‐time acceleration. The recent observational data to the considered model especially the bounds on model parameters is applied in detail. Furthermore, we analyze the cosmological behavior of the deceleration, effective equation of state and total equation of state parameters. However, it is seen that the deceleration parameter depicts the transition from deceleration to acceleration and the effective dark sector shows a quintessence‐like evolution.

Perturbative resonance in WIMP paradigm and its cosmological implications on cosmic reheating and primordial gravitational wave detection

We investigate the co-evolution of dark matter (DM) density perturbation and metric perturbation in the WIMP paradigm. Instead of adopting the conventional assumption that DM starts out in thermal equilibrium, we propose a simple phase of DM production for the WIMP paradigm and extend our analysis to this phase. Being free from the envelop of thermal equilibrium, an amplified perturbative resonance between DM density perturbation and scalar modes of metric perturbation takes place during the DM production phase, and consequently results in a suppression of the tensor-to-scalar ratio of metric perturbation. By specifying the cosmic background with a typical realization of cosmic reheating, we establish a relation between DM particle mass m χ and the tensor-to-scalar ratio r in the WIMP paradigm, which also contains two reheating parameters, the reheating temperature T R f and the dissipative constant Γ 0 . Notably, for a sizeable parameter region of WIMP candidate and cosmic reheating, this relation predicts a smaller value of r in comparing with the conventional expectation obtained by assuming DM starts out in thermal equilibrium. Once the suppression of r is measured in future observations of primordial gravitational wave in CMB, this relation can be used to constrain m χ , T R f and Γ 0 in principle.

Cosmology in Rastall theory with non-minimal matter coupling

In this paper we will consider cosmological implications of the Rastall theory with a non-minimal coupling with baryonic matter fields. In Rastall theory, the matter energy-momentum tensor is not conserved and the non-conservation is related to the curvature. We will generalize this relation to become dependent on both curvature and matter fields. Cosmology of the model shows more matter abundance compared to the model. We will show that the dynamical system of the model is the same as with an additional degree of freedom.

Viscous cosmology in f(T) gravity

We propose a new model for the viscosity of cosmic matters, which can be applied to different epochs of the universe. Using this model, we include the bulk viscosities as practical corrections to the perfect fluid models of the baryonic and dark matters since the material fluids in the real world may have viscosities due to thermodynamics. Such inclusion is put to the test within the framework of f(T) gravity that is proved to be successful in describing the cosmic acceleration, where T denotes the torsion scalar. We perform an observational fit to our model and constrain the cosmological and model parameters by using various latest cosmological datasets. Based on the fitting result, we discuss several cosmological implications including the dissipation of matters, the evolutionary history of the universe, f(T) modification as an effective dark energy, and the Hubble tension problem. The corresponding findings are (i) The late time dissipation will make the density parameters of the matters vanish in the finite future. Moreover, the density ratio between the baryonic and dark matters will change over time. (ii) The radiation dominating era, matter dominating era and the accelerating era can be recovered and the model can successfully describe the known history of the universe. (iii) The f(T) modification is the main drive of the acceleration expansion and currently mimics a phantom-like dark energy. But the universe will eventually enter a de Sitter expansion phase. (iv) The Hubble tension between local and global observations can be significantly alleviated in our model.

Observational constraints and cosmological implications of NLE model with variable G

Observational constraints and cosmological implications of NLE model with variable G

Palatini formulation of the conformally invariant fleft( R,L_mright) gravity theory

We investigate the field equations of the conformally invariant models of gravity with curvature-matter coupling, constructed in Weyl geometry, using the Palatini formalism. We consider the case in which the Lagrangian is given by the sum of the square of the Weyl scalar, the strength of the field associated to the Weyl vector, and a conformally invariant geometry-matter coupling term, constructed from the matter Lagrangian and the Weyl scalar. After substituting the Weyl scalar in terms of its Riemannian counterpart, the quadratic action is defined in Riemann geometry and involves a nonminimal coupling between the Ricci scalar and the matter Lagrangian. For the sake of generality, a more general Lagrangian, in which the Weyl vector is nonminimally coupled with an arbitrary function of the Ricci scalar, is also considered. By varying the action independently with respect to the metric and the connection, the independent connection can be expressed as the Levi-Civita connection of an auxiliary Ricci scalar- and Weyl vector-dependent metric, which is related to the physical metric by means of a conformal transformation. The field equations are obtained in both the metric and the Palatini formulations. The cosmological implications of the Palatini field equations are investigated for three distinct models corresponding to different forms of the coupling functions. A comparison with the standard Lambda CDM model is also performed, and we find that the Palatini type cosmological models can give an acceptable description of the observations.

Late-time cosmology with phantom dark-energy in f(Q) gravity

Motivated by the exciting features and a recent proposed general form of the function of non-metricity scalar Q, we investigate the cosmological implications in f(Q) gravity, through the resulting effective dark energy sector, extracting analytical expressions for the dark energy density, equation-of-state and the deceleration parameters. We show that even in the absence of a cosmological constant, the universe exhibits the usual thermal history, with the sequence of matter and dark energy eras, and the dark-energy equation-of-state parameter always lie in the phantom regime. Additionally, calculating the age of the universe, through the extracted analytical equations of the scenario at hand, we show that the result coincide with the value corresponding to ΛCDM scenario within 1σ. Moreover, we show the excellent agreement of the scenario at hand with Supernovae type Ia observational data. Lastly, comparing the cosmological behavior in the case of the absence of an explicit cosmological constant, with the one of the presence of a cosmological constant we show that f(Q) gravity can mimic the cosmological constant in a very efficient way, providing very similar behavior, revealing the advantages and capabilitites of the scenario at hand.

Tripling down on the W boson mass

A new precision measurement of the W boson mass has been announced by the CDF collaboration, which strongly deviates from the Standard Model prediction. In this article, we study the implications of this measurement on the parameter space of the SU(2)_L triplet extension (with hypercharge Y=1) of the Standard Model Higgs sector, focusing on a limit where the new triplet is approximate {mathbb {Z}}_2-odd while the SM is {mathbb {Z}}_2-even. We study the compatibility of the triplet spectrum preferred by the W boson mass measured by the CDF-II experiment with other electroweak precision observables and Higgs precision data. We comprehensively consider the signals of new Higgs states at the LHC and highlighted the promising search channels. In addition, we also investigate the cosmological implications of the case in which the lightest new Higgs particle is either late decaying or cosmologically stable.

Shedding Light to the Dark Sides of the Universe: Cosmology from Strong Interactions

The basic aim of this Special Issue was to reflect upon the modern status of research on strong interactions and their implications in Cosmology [...]

Sign Switching Dark Energy from a Running Barrow Entropy

Barrow proposed that the area law of the entropy associated with a horizon might receive a “fractal correction” due to quantum gravitational effects—in place of S∝A, we have instead S∝A1+δ/2, where 0⩽δ⩽1 measures the deviation from the standard area law (δ=0). Based on black hole thermodynamics, we argue that the Barrow entropy should run (i.e., energy scale dependent), which is reasonable given that quantum gravitational corrections are expected to be important only in the high-energy regime. When applied to the Friedmann equation, we demonstrate the possibility that such a running Barrow entropy index could give rise to a dynamical effective dark energy, which is asymptotically positive and vanishing, but negative at the Big Bang. Such a sign switching dark energy could help to alleviate the Hubble tension. Other cosmological implications are discussed.

Axion wormholes with massive dilaton

If Euclidean wormholes contribute meaningfully to the path integral of quantum gravity they can have important implications for particle physics and cosmology. The dominant effects arise from wormholes whose sizes are comparable to the cut-off scale of effective field theory, for which ultraviolet corrections become relevant. We study corrections to classical axion wormhole solutions in string motivated scenarios in which the dilaton partner of the axion becomes massive. We find corrections near the neck region which are consistent with a recent version of the weak gravity conjecture for axions.