Standard Thermal History Research Articles

Modified cosmology from quantum deformed entropy

Jalalzadeh (2022), established that the thermodynamical entropy of a quantum-deformed black hole with horizon area A can be written as Sq=πsinA8GN/sinπ2N, where N=Lq2/LP2, LP being the Planck length and Lq denoting, generically, the q-deformed cosmic event horizon distance Lq. Motivated by this, we now extend the framework constructed in Jalalzadeh (2022) towards the Friedmann and Raychaudhuri equations describing spatially homogeneous and isotropic universe dynamics. Our procedure in this paper involves a twofold assumption. On the one hand, we take the entropy associated with the apparent horizon of the Robertson–Walker universe in the form of the aforementioned expression. On the other hand, we assume that the unified first law of thermodynamics, dE=TdS+WdV, holds on the apparent horizon. Subsequently, we find a novel modified cosmological scenario characterized by quantum-deformed (q-deformed) Friedmann and Raychaudhuri equations containing additional components that generate an effective dark energy sector. Our results indicate an effective dark energy component, which can explain the Universe’s late-time acceleration. Moreover, the Universe follows the standard thermal history, with a transition redshift from deceleration to acceleration at ztran=0.5. More precisely, according to our model, at a redshift of z=0.377, the effective dark energy dominates with a de Sitter universe in the long run. We include the evolution of luminosity distance, μ, the Hubble parameter, H(z), and the deceleration parameter, q(z), versus redshift. Finally, we have conducted a comparative analysis of our proposed model with others involving non-extensive entropies.

Non-minimally coupled Natural Inflation: Palatini and Metric formalism with the recent BICEP/Keck

In this work, we show the effect of the non-minimal coupling ξϕ 2 R on the inflationary parameters by considering the single-field inflation and present the inflationary predictions of the appealing potential for the particle physics viewpoint: Natural Inflation, an axion-like inflaton which has a cosine-type periodic potential and the inflaton naturally emerges as a pseudo-Nambu-Goldstone boson with a spontaneously broken global symmetry. We present the inflationary predictions for this potential, ns , r, and α = dns /d ln k. In addition, we assume standard thermal history after inflation, and using this, for considered potential, we show compatible regions for the ns , r within the recent BICEP/Keck results.

Kaniadakis holographic dark energy and cosmology

We construct a holographic dark energy scenario based on Kaniadakis entropy, which is a generalization of Boltzmann-Gibbs entropy that arises from relativistic statistical theory and is characterized by a single parameter K which quantifies the deviations from standard expressions, and we use the future event horizon as the Infrared cutoff. We extract the differential equation that determines the evolution of the effective dark energy density parameter, and we provide analytical expressions for the corresponding equation-of-state and deceleration parameters. We show that the universe exhibits the standard thermal history, with the sequence of matter and dark-energy eras, while the transition to acceleration takes place at zapprox 0.6. Concerning the dark-energy equation-of-state parameter we show that it can have a rich behavior, being quintessence-like, phantom-like, or experience the phantom-divide crossing in the past or in the future. Finally, in the far future dark energy dominates completely, and the asymptotic value of its equation of state depends on the values of the two model parameters.

Dark gravitational sectors on a generalized scalar-tensor vector bundle model and cosmological applications

In this work we present the foundations of generalized scalar-tensor theories arising from vector bundle constructions, and we study the kinematic, dynamical, and cosmological consequences. In particular, over a pseudo-Riemannian space-time base manifold, we define a fiber structure with two scalar fields. The resulting space is a 6-dimensional vector bundle endowed with a nonlinear connection. We provide the form of the geodesics and the Raychaudhuri and general field equations, both in the Palatini and metrical methods. When applied at a cosmological framework, this novel geometrical structure induces extra terms in the modified Friedmann equations, leading to the appearance of an effective dark energy sector, as well as of an interaction of the dark mater sector with the metric. We show that we can obtain the standard thermal history of the universe, with the sequence of matter and dark-energy epochs, and furthermore the effective dark-energy equation-of-state parameter can lie in the quintessence or phantom regimes, or exhibit the phantom-divide crossing.

F(T) cosmology: from Pseudo-Bang to Pseudo-Rip

We investigate the complete universe evolution in the framework off(T) cosmology. We first study the requirements at thekinematic level and we introduce a simple scale factor with the necessaryfeatures. Performing a detailed analysis of the phaseportrait we show that the universe begins in the infinite past from aphase where thescale factor goes to zero but the Hubble parameter goes to a constant, and itsderivative to zero. Since these features resemble those of the Pseudo-Ripfate but in a revered way, we call this initial phaseas Pseudo-Bang. Then the universe evolves in a first inflationary phase, acosmological turnaround and a bounce, after which we have asecond inflationary regime with a successful exit. Subsequently we obtainthe standard thermal history and the sequence of radiation, matter andlate-time acceleration epochs, showing that the universe will result inan everlasting Pseudo-Rip phase. Finally, taking advantage of the fact thatthe field equations of f(T) gravity are of second order, and therefore thecorresponding autonomous dynamical system is one dimensional, we incorporate the aforementioned kinematicfeatures and we reconstruct the specific f(T)form that can dynamically generate the Pseudo-Bang cosmological scenario. Lastly, we examine the evolution of the primordial fluctuationsshowing that they are initially sub-horizon, and we show thatthe total fluid does not exhibit any singular behaviour at thephantom crossing points, while the torsional fluid experiencesthem as Type II singular phases.

Multimessenger probes of inflationary fluctuations and primordial black holes

Next generation cosmic microwave background spectral distortion and pulsar timing array experiments have the potential to probe primordial fluctuations at small scales with remarkable sensitivity. We demonstrate the potential of these probes to either detect signatures of primordial black holes (PBHs) sourced from primordial overdensities within the standard thermal history of the universe over a 13-decade mass range ${\cal O}(0.1-10^{12})M_\odot$, or constrain their existence to a negligible abundance. Our conclusions are based only on global cosmological signals, and are robust under changes in i) the statistical properties of the primordial density fluctuations (whether Gaussian or non-Gaussian), ii) the merger and accretion history of the PBHs and assumptions about associated astrophysical processes, and iii) clustering statistics. Any positive detection of enhanced primordial fluctuations at small scales would have far-reaching implications from the content of dark matter to origin of BHs in the centers of galaxies, and to the field content of the inflation. On the other hand, their non-detection would also have important corollaries. For example, non-detection up to forecast sensitivities would tell us that PBHs larger than a fraction of a solar mass can constitute no more than a negligible fraction of dark matter. Moreover, non-detection will also rule out the scenario that PBHs generated by primordial overdensities could be the progenitors of super-massive black holes (SMBHs), of topical interest as there are only a few widely accepted proposals for the formation of SMBHs, an even more pressing question after the detection of active galactic nuclei over a billion solar masses at redshifts $z \geq 7$. Finally, non-detection sets the strongest bounds on the amplitude of small scale inflationary fluctuations for over 6 decades.

A dark clue to seesaw and leptogenesis in a pseudo-Dirac singlet doublet scenario with (non)standard cosmology

We propose an appealing alternative scenario of leptogenesis assisted by dark sector which leads to the baryon asymmetry of the Universe satisfying all theoretical and experimental constraints. The dark sector carries a non minimal set up of singlet doublet fermionic dark matter extended with copies of a real singlet scalar field. A small Majorana mass term for the singlet dark fermion, in addition to the typical Dirac term, provides the more favourable dark matter of pseudo-Dirac type, capable of escaping the direct search. Such a construction also offers a formidable scope to radiative generation of active neutrino masses. In the presence of a (non)standard thermal history of the Universe, we perform the detailed dark matter phenomenology adopting the suitable benchmark scenarios, consistent with direct detection and neutrino oscillations data. Besides, we have demonstrated that the singlet scalars can go through CP-violating out of equilibrium decay, producing an ample amount of lepton asymmetry. Such an asymmetry then gets converted into the observed baryon asymmetry of the Universe through the non-perturbative sphaleron processes owing to the presence of the alternative cosmological background considered here. Unconventional thermal history of the Universe can thus aspire to lend a critical role both in the context of dark matter as well as in realizing baryogenesis.

Superheavy dark matter from string theory

Explicit string models which can realize inflation and low-energy supersymmetry are notoriously difficult to achieve. Given that sequestering requires very specific configurations, supersymmetric particles are in general expected to be very heavy implying that the neutralino dark matter should be overproduced in a standard thermal history. However, in this paper we point out that this is generically not the case since early matter domination driven by string moduli can dilute the dark matter abundance down to the observed value. We argue that generic features of string compactifications, namely a high supersymmetry breaking scale and late time epochs of modulus domination, might imply superheavy neutralino dark matter with mass around 1010–1011 GeV. Interestingly, this is the right range to explain the recent detection of ultra-high-energy neutrinos by IceCube and ANITA via dark matter decay.

Kinetics of hydrocarbon generation from the marine Ordovician Goldwyer Formation, Canning Basin, Western Australia

Pyrolysis and bulk kinetic studies were used to investigate the hydrocarbon generation potential and source rock organofacies variability of marine organic-rich rocks from the Middle Ordovician (Darriwilian) Goldwyer Formation in the Canning Basin, Western Australia. Rock-Eval pyrolysis results for the analysed immature to mid-mature calcareous mudstones imply that the upper Goldwyer Sequence I contains oil-prone type I kerogen, while the lower Goldwyer Sequence III contains type II/III oil- and gas-prone kerogen. This is supported by pyrolysis gas chromatography (Py-GC) results that show the presence of homogenous organofacies in the Goldwyer Sequence I having aliphatic molecular signatures, possibly due to selective preservation of lipids derived from Gloeocapsomorpha prisca (G. prisca). The heterogeneous organofacies of the Goldwyer Sequence III contain aromatic moieties in similar abundance to the aliphatic compounds. The calcareous claystones of the Goldwyer Sequence I have the capacity to generate low wax paraffinic oil, whereas the Goldwyer Sequence III has potential for paraffinic-naphthenic-aromatic (P-N-A) low wax oils, gas, and condensate.The temperature for hydrocarbon generation for the type I kerogen, assuming a constant geological heating rate of 3 °C/my, is estimated to occur over a narrow interval between 145 °C and 170 °C for the Goldwyer Sequence I samples. Generation from the type II/III kerogen occurs from 100 °C to 160 °C in the Goldwyer Sequence III samples which are significantly less thermally stable than the Goldwyer Sequence I samples. The kinetic results for both sequences were used in standard thermal and burial history plots to evaluate their transformation ratio and hydrocarbon generative potential. This provided basin-specific kinetic inputs for burial history modelling and better constraint on kerogen transformation and hydrocarbon generation on the Broome Platform.

Friedmann-like universes with torsion

We consider spatially homogeneous and isotropic cosmologies with non-vanishing torsion, which assumes a specific form due to the high symmetry of these universes. Using covariant and metric-based techniques, we derive the torsional versions of the continuity, the Friedmann and the Raychaudhuri equations. These show how torsion can drastically change the standard evolution of the Friedmann models, by playing the role of the spatial curvature or that of the cosmological constant. We find, for example, that torsion alone can lead to exponential expansion and thus make the Einstein–de Sitter universe look like the de Sitter cosmos. Also, by modifying the expansion rate of the early universe, torsion could have affected the primordial abundance of helium-4. We show, in particular, that torsion can reduce the production of primordial helium-4, unlike other changes to the standard thermal history of the universe. These theoretical results allow us to impose strong observational bounds on the relative strength of the associated torsion field, confining its ratio to the Hubble rate within the narrow interval (-,0.005813,,+,0.019370) around zero. Finally, turning to static spacetimes, we demonstrate that there exist torsional analogues of the Einstein static universe with all three types of spatial geometry. These models can be stable when the torsion field and the universe’s spatial curvature have the appropriate profiles.

The effect of melting conditions on the iPB-1 structure and the II → I phase transformation rate

The melting conditions, mainly the temperature and time, influence a polymer samples characteristics. Changes in normal or repeated melting procedures can influence the crystallinity, phase, structure, phase transformation rate and type of polymorphous polymers as was demonstrated here on a sample of isotactic polybutene-1. In the treatment temperature range 120–130 °C and 5 min treatment time the phase II → I transformation type after crystallization was neutral (N), which was faster than the type M (slow transformation type), which took place when the treatment temperature was 160 °C or higher. The change from N to M transformation type involved the formation of an induction period. During this period some configuration or crystal changes can take place in the sample, and the newly formed structures block the phase transformation nuclei until all of the newly formed blocking structures have reacted with the transformation nuclei and then the formation of phase I nuclei and their growth can start again. Based on the results here, as an initial standard thermal history for molded iPB-1 samples, avoiding the M transformation type, holding 5 min at 120–130 °C, followed by free cooling to room temperature and pressure is recommended.

Comment on “Kinetic decoupling of WIMPs: Analytic expressions”

Visinelli and Gondolo (2015, hereafter VG15) derived analytic expressions for the evolution of the dark matter temperature in a generic cosmological model. They then calculated the dark matter kinetic decoupling temperature $T_{\mathrm{kd}}$ and compared their results to the Gelmini and Gondolo (2008, hereafter GG08) calculation of $T_{\mathrm{kd}}$ in an early matter-dominated era (EMDE), which occurs when the Universe is dominated by either a decaying oscillating scalar field or a semistable massive particle before Big Bang nucleosynthesis. VG15 found that dark matter decouples at a lower temperature in an EMDE than it would in a radiation-dominated era, while GG08 found that dark matter decouples at a higher temperature in an EMDE than it would in a radiation-dominated era. VG15 attributed this discrepancy to the presence of a matching constant that ensures that the dark matter temperature is continuous during the transition from the EMDE to the subsequent radiation-dominated era and concluded that the GG08 result is incorrect. We show that the disparity is due to the fact that VG15 compared $T_\mathrm{kd}$ in an EMDE to the decoupling temperature in a radiation-dominated universe that would result in the same dark matter temperature at late times. Since decoupling during an EMDE leaves the dark matter colder than it would be if it decoupled during radiation domination, this temperature is much higher than $T_\mathrm{kd}$ in a standard thermal history, which is indeed lower than $T_{\mathrm{kd}}$ in an EMDE, as stated by GG08.

Neutrino Physics from the Cosmic Microwave Background and Large-Scale Structure

Cosmology and neutrino physics have converged into a recent discovery era. The success of the standard model of cosmology in explaining the cosmic microwave background and cosmological large-scale structure data allows for the possibility of measuring the absolute neutrino mass and providing exquisite constraints on the number of light degrees of freedom, including neutrinos. This sensitivity to neutrino physics requires the validity of some of the assumptions, including general relativity, inflationary cosmology, and standard thermal history, many of which can be tested with cosmological data. This sensitivity is also predicated on the robust handling of systematic uncertainties associated with different cosmological observables. We review several past, current, and future measurements of the cosmic microwave background and cosmological large-scale structure that allow us to do fundamental neutrino physics with cosmology.

Breaking Be: a sterile neutrino solution to the cosmological lithium problem

The possibility that the so-called ``lithium problem'', i.e., the disagreement between the theoretical abundance predicted for primordial 7Li assuming standard nucleosynthesis and the value inferred from astrophysical measurements, can be solved through a non-thermal Big Bang Nucleosynthesis (BBN) mechanism has been investigated by several authors. In particular, it has been shown that the decay of a MeV-mass particle, like, e.g., a sterile neutrino, decaying after BBN not only solves the lithium problem, but also satisfies cosmological and laboratory bounds, making such a scenario worth to be investigated in further detail. In this paper, we constrain the parameters of the model with the combination of current data, including Planck 2015 measurements of temperature and polarization anisotropies of the Cosmic Microwave Background (CMB), FIRAS limits on CMB spectral distortions, astrophysical measurements of primordial abundances and laboratory constraints. We find that a sterile neutrino with mass MS = 4.35−0.17+0.13 MeV (at 95% c.l.), a decay time τS = 1.8−1.3+2.5 · 105 s (at 95% c.l.) and an initial density n̄S/n̄cmb = 1.7−0.6+3.5 · 10−4 (at 95% c.l.) in units of the number density of CMB photons, perfectly accounts for the difference between predicted and observed 7Li primordial abundance. This model also predicts an increase of the effective number of relativistic degrees of freedom at the time of CMB decoupling ΔNeffcmb ≡ Neffcmb −3.046 = 0.34−0.14+0.16 at 95% c.l.. The required abundance of sterile neutrinos is incompatible with the standard thermal history of the Universe, but could be realized in a low reheating temperature scenario. We also provide forecasts for future experiments finding that the combination of measurements from the COrE+ and PIXIE missions will allow to significantly reduce the permitted region for the sterile lifetime and density.

Improving naturalness in gauge mediation with nonunified messenger sectors

We study models of gauge-mediated supersymmetry breaking with messengers that do not belong to complete representations of grand-unified gauge groups. We show that certain setups characterized by heavy Wino can greatly improve the fine tuning with respect to models with unified messengers, such as minimal gauge mediation. The typical models with low tuning feature multi-TeV superparticles, with the exception of the Higgsinos and possibly Bino and right-handed sleptons. As a consequence, the absence of signals for supersymmetry at the LHC is trivially accommodated in our framework. On the other hand, testing these models will be challenging at the LHC. We finally show that the gravitino can be a consistent candidate for cold dark matter, provided a rather low reheating temperature, if a standard thermal history of the universe is assumed.

Gravitational baryogenesis after anisotropic inflation

The gravitational baryogensis may not generate a sufficient baryon asymmetry in the standard thermal history of the Universe when we take into account the gravitino problem. Hence it has been suggested that anisotropy of the Universe can enhance the generation of the baryon asymmetry through the increase of the time change of the Ricci scalar curvature. We study the gravitational baryogenesis in the presence of anisotropy, which is produced at the end of an anisotropic inflation. Although we confirm that the generated baryon asymmetry is enhanced compared with the original isotropic cosmological model, taking into account the constraint on the anisotropy by the recent CMB observations, we find that it is still difficult to obtain the observed baryon asymmetry only through the gravitational baryogenesis without suffering from the gravitino problem.

(O)Mega split

We study two realisations of the Fake Split Supersymmetry Model (FSSM), the simplest model that can easily reproduce the experimental value of the Higgs mass for an arbitrarily high supersymmetry scale, as a consequence of swapping higgsinos for equivalent states, fake higgsinos, with suppressed Yukawa couplings. If the LSP is identified as the main Dark matter component, then a standard thermal history of the Universe implies upper bounds on the supersymmetry scale, which we derive. On the other hand, we show that renormalisation group running of soft masses above the supersymmetry scale barely constrains the model - in stark contrast to Split Supersymmetry - and hence we can have a "Mega Split" spectrum even with all of these assumptions and constraints, which include the requirements of a correct relic abundance, a gluino life-time compatible with Big Bang Nucleosynthesis and absence of signals in present direct detection experiments of inelastic dark matter. In an appendix we describe a related scenario, Fake Split Extended Supersymmetry, which enjoys similar properties.

Quintessential inflation with canonical and noncanonical scalar fields and Planck 2015 results

We investigate two classes of models of quintessential inflation, based upon canonical as well as noncanonical scalar fields. In particular, introducing potentials steeper than the standard exponential, we construct models that can give rise to a successful inflationary phase, with signatures consistent with Planck 2015 results. Additionally, using nonminimal coupling of the scalar field with massive neutrino matter, we obtain the standard thermal history of the Universe, with late-time cosmic acceleration as the last stage of evolution. In both cases, inflation and late-time acceleration are connected by a tracker solution.

Scalar modes of the relic gravitons

In conformally flat background geometries the long wavelength gravitons can be described in the fluid approximation and they induce scalar fluctuations both during inflation and in the subsequent radiation-dominated epoch. While this effect is minute and suppressed for a de Sitter stage of expansion, the fluctuations of the energy-momentum pseudo-tensor of the graviton fluid lead to curvature perturbations that increase with time all along the post-inflationary evolution. An explicit calculation of these effects is presented for a standard thermal history and it is shown that the growth of the curvature perturbations caused by the long wavelength modes is approximately compensated by the slope of the power spectra of the energy density, pressure and anisotropic stress of the relic gravitons.

ϕ2inflation at its endpoint

In the simplest inflationary model $V=\frac12 m^2\phi^2$, we provide a prediction accurate up to $1\%$ for the spectral index $n_s$ and the tensor-to-scalar ratio $r$ assuming instantaneous reheating and a standard thermal history: $n_s = 0.9668\pm0.0003$ and $r=0.131\pm 0.001$. This represents the simplest and most informative point in the $(n_s,r)$ plane. The result is independent of the details of reheating (or preheating) provided the conversion to radiation is sufficiently fast. A slower reheating or a modified post-inflationary evolution push towards smaller $n_s$ (and larger $r$), so that our prediction corresponds to the maximum $n_s$ (and minimum $r$) for the quadratic potential. We also derive similar results for a general $V \propto \phi^p$ potential.