Alternative kind of hydrogen atoms as a possible explanation for the latest puzzling observation of the 21 cm radio line from the early Universe

There is a puzzling astrophysical result concerning the latest observation of the absorption profile of the redshifted radio line 21 cm from the early Universe(as described in Bowman et al.). The amplitude of the profile was more than a factor of two greater than the largest predictions. This could mean that the primordial hydrogen gas was much cooler than expected. Some explanations in the literature suggested a possible cooling of baryons either by unspecified dark matter particles or by some exotic dark matter particles with a charge a million times smaller than the electron charge. Other explanations required an additional radio background. In the present paper, we entertain a possible different explanation for the above puzzling observational result: the explanation is based on the alternative kind of hydrogen atoms(AKHA),whose existence was previously demonstrated theoretically, as well as by the analysis of atomic experiments. Namely, the AKHA are expected to decouple from the cosmic microwave background(CMB) much earlier(in the course of the Universe expansion) than usual hydrogen atoms, so that the AKHA temperature is significantly lower than that of usual hydrogen atoms. This seems to lower the excitation(spin) temperature of the hyperfine doublet(responsible for the 21 cm line) sufficiently enough for explaining the above puzzling observational result. This possible explanation appears to be more specific and natural than the previous possible explanations. Further observational studies of the redshifted 21 cm radio line from the early Universe could help to verify which explanation is the most relevant.

A Theory of Our Universe

Contemporary theories of our Universe, such as the Friedmann-Lemaître-Robertson-Walker (FLRW) model of the cosmos, assume that time marches on at a uniform, constant pace from its very beginning. But what if that is not the case? It is proposed that our Universe is not a “Big Bang”, but rather a “Big Rollout” in space and time, spacetime, from the shortest meaningful length, Planck Length, and the shortest meaningful measure of time, Planck Time. It is speculated that time and dimensions, spacetime, grow in concert very rapidly at first. The fundamental equation, which relates the change in the space dimensions to the change in the speed of time at the beginning of time for the new Theory, is derived. Spacetime rolls out initially at light speed. As time increases, the rate of change of the speed of time could be erratic, that is although in general, it slows (rate of time slows approaching zero at the end of time), its rate of change could decelerate, pause or perhaps accelerate for a while, no need however, for dark matter or dark energy.

A new interpretation of zero Lyapunov exponents in BKL time for Mixmaster cosmology

A global relationship between cosmological time and Belinskii-Khalatnikov -Lifshitz （BKL） time during the entire evolution of the Mixmaster Bianchi IX universe is used to explain why all the Lyapunov exponents are zero at the BKL time. The actual reason is that the domain of the cosmological time is finite as the BKL time runs from minus infinity to infinity.

String cosmological models in the Brans-Dicke theory for five-dimensional space-time

Five-dimensional space-time string cosmological models generated by a cloud of strings with particles attached to them are studied in the Brans-Dicke theory. We obtain two types of interesting models by taking up the cases of geometric strings （or Nambu strings） and p-strings （Takabayasi strings）, and study their different physi- cal and dynamical properties. The roles of the scalar field in getting different phases, such as the inflationary phase and the string-dominated phase, are discussed. An in- teresting feature obtained here is that in one of the models there is a ＂bounce＂ at a particular instant of its evolution.

Predicting Dark Energy Survey Results Using the Flat Space Cosmology Model

The Flat Space Cosmology (FSC) model is utilized to show how this model predicts the value of the Hubble parameter at each epoch of cosmic expansion. Specific attention in this paper is given to correlating the observable galactic redshifts since the beginning of the “cosmic dawn” reionization epoch. A graph of the log of the Hubble parameter as a function of redshift z is presented as the FSC prediction of the pending Dark Energy Survey results. In the process, it is discovered that the obvious tension between the SHOES local Hubble constant value and the 2018 Planck Survey and the 2018 Dark Energy Survey global Hubble constant values may be explained by a time-variable, scalar, Hubble parameter acting in accordance with the FSC model.

C-field cosmological models:revisited

We investigate plane symmetric spacetime filled with perfect fluid in the C-field cosmology of Hoyle and Narlikar. A new class of exact solutions has been obtained by considering the creation field C as a function of time only. To get the deterministic solution, it has been assumed that the rate of creation of matter-energy density is proportional to the strength of the existing C-field energy density. Several physical aspects and geometrical properties of the models are discussed in detail, especially showing that some of our solutions of C-field cosmology are free from singularity in contrast to the Big Bang cosmology. A comparative study has been carried out between two models, one singular and the other nonsingular, by contrasting the behaviour of the physical parameters. We note that the model in a unique way represents both the features of the accelerating as well as decelerating universe depending on the parameters and thus seems to provide glimpses of the oscillating or cyclic model of the universe without invoking any other agent or theory in allowing cyclicity.

Cosmological perturbations in a noncommutative braneworld inflation

We use the smeared, coherent state picture of noncommutativity to study evolution of perturbations in a noncommutative braneworld scenario. Within the stan- dard procedure of studying braneworld cosmological perturbations, we study the evo- lution of the Bardeen metric potential and curvature perturbations in this model. We show that in this setup, the early stage of the universe＇s evolution has a transient phan- tom evolution with imaginary effective sound speed.

A Cosmological Model without Singularity Based on RW Metric (1)

A new conjecture is proposed that there are two sorts of matter called s-matter and v-matter which are symmetric, whose masses are positive, but whose gravitational masses are opposite to each other. Based on the conjecture and the SUS(5) × SUV(5) gauge group, a cosmological model has been constructed and the following inferences have been derived. There are two sorts of symmetry breaking called V-breaking and S-breaking. In theV-breaking, SUV(5) breaks finally to SUV(3) × UV(1) so that v-particles get their masses and form v-atoms andv-galaxies etc., while SUS(5) still holds so that s-fermions and s-gauge bosons are massless and form SUS(5)color-singlets. There is no interaction among the SUS(5) color-singlets except gravitation so that they distribute loosely in space, cannot be observed, and cause space to expand with an acceleration. Evolution of the universe is explained. There is no space-time singularity. There are the highest temperature and the least scale in the universe. It is impossible that the Plank temperature and length are arrived. A formula is obtained which describes the relation between a luminous distance and its redshift. A huge void is not empty, and is equivalent to a huge concave lens. The densities of hydrogen in the huge voids must be much less than that predicted by the conventional theory. The gravitation between two galaxies whose distance is long enough will be less than that predicted by the conventional theory. A black hole with its big enough mass will transform into a white hole.

Bianchi-V string cosmological model and late time acceleration

We have searched for the existence of the late time acceleration of the universe with string fluid as the source of matter in Bianchi-V space-time. To derive a deterministic solution, we choose the scale factor to be an increasing function of time that yields a time dependent deceleration parameter, representing a model which generates a universe showing a transition from an early decelerating phase to a recent accelerating phase. The study reveals that strings dominate the early universe and eventually disappear from the universe for sufficiently large times, i.e. in the present epoch. This picture is consistent with current astronomical observations. The physical behavior of the universe is discussed in detail.

Anisotropic massive strings in the scalar-tensor theory of gravitation

We present the model of an anisotropic universe with string fluid as the source of matter within the framework of the scalar-tensor theory of gravitation. An exact solution of field equations is obtained by applying Berman＇s law of variation to Hubble＇s parameter which yields a constant value of the deceleration parameter. The nature of classical potential is examined for the model under consideration. It has also been found that the massive strings dominate in the early universe and finally disap-pear from the universe. This is in agreement with current astronomical observations. The physical and dynamical properties of the model are also discussed.

Space-Time Geometry of Quark and Strange Quark Matter

We study quark and strange quark matter in the context of general relativity. For this purpose, we solve Einstein＇s field equations for quark and strange quark matter in spherical symmetric space-times. We analyze strange quark matter for the different equations of state （EOS） in the spherical symmetric space-times, thus we are able to obtain the space-time geometries of quark and strange quark matter. Also, we discuss the features of the obtained solutions. The obtained solutions are consistent with the results of Brookhaven Laboratory, i.e. the quark-gluon plasma has a vanishing shear （i.e. quark-gluon plasma is perfect）.

Primordial black holes

Primordial black holes （PBHs） are a profound signature of primordial cosmological structures and provide a theoretical tool to study nontrivial physics of the early Universe. The mechanisms of PBH formation are discussed and observational constraints on the PBH spectrum, or effects of PBH evaporation, are shown to restrict a wide range of particle physics models, predicting an enhancement of the ultraviolet part of the spectrum of density perturbations, early dust-like stages, first order phase transitions and stages of superheavy metastable particle dominance in the early Universe. The mechanism of closed wall contraction can lead, in the inflationary Universe, to a new approach to galaxy formation, involving primordial clouds of massive BHs created around the intermediate mass or supermassive BH and playing the role of galactic seeds.

Cosmic microwave background constraints on the tensor-to-scalar ratio

One of the main goals of modern cosmic microwave background （CMB） missions is to measure the tensor-to-scalar ratio r accurately to constrain inflation models. Due to ignorance about the reionization history Xe （z）, this analysis is usu- ally done by assuming an instantaneous reionization Xe （z） which, however, can bias the best-fit value of r. Moreover, due to the strong mixing of B-mode and E-mode polarizations in cut-sky measurements, multiplying the sky coverage fraction fsky by the full-sky likelihood would not give satisfactory results. In this work, we forecast constraints on r for the Planck mission taking into account the general reionization scenario and cut-sky effects. Our results show that by applying an N-point interpo- lation analysis to the reionization history, the bias induced by the assumption of in- stantaneous reionization is removed and the value of r is constrained within 5% error level, if the true value of r is greater than about 0.1.

Galaxy formation in the reionization epoch as hinted by WideField Camera 3 observations of the Hubble Ultra Deep Field

We present a large sample of candidate galaxies at z ≈ 7 - 10, selected in the Hubble Ultra Deep Field using the new observations of the Wide Field Camera 3 that was recently installed on the Hubble Space Telescope. Our sample is composed of 20 z850-dropouts （four new discoveries）, 15 Y105-dropouts （nine new discoveries） and 20 J125-dropouts （all new discoveries）. The surface densities of the Z850-dropouts are close to what was predicted by earlier studies, however, those of the Y105- and J125-dropouts are quite unexpected. While no Y105- or J125-dropouts have been found at AB ≤ 28.0 mag, their surface densities seem to increase sharply at fainter levels. While some of these candidates seem to be close to foreground galaxies and thus could possibly be gravitationally lensed, the overall surface densities after excluding such cases are still much higher than what would be expected if the luminosity function does not evolve from z ～ 7 to 10. Motivated by such steep increases, we tentatively propose a set of Schechter function parameters to describe the luminosity functions at z ≈8 and 10. As compared to their counterpart at z ≈ 7, here L^＊ decreases by a factor of ～ 6.5 and Ф^＊ increases by a factor of 17-90. Although such parameters are not yet demanded by the existing observations, they are allowed and seem to agree with the data better than other alternatives. If these luminosity functions are still valid beyond our current detection limit, this would imply a sudden emergence of a large number of low-luminosity galaxies when looking back in time to z ≈ 10, which, while seemingly exotic, would naturally fit in the picture of the cosmic hydrogen reionization. These early galaxies could easily account for the ionizing photon budget required by the reionization, and they would imply that the global star formation rate density might start from a very high value at z ≈ 10, rapidly reach the minimum at z≈ 7, and start to rise again towards z ≈ 6. In this scenario, the majority of the stellar mass that the universe assembled through the reionization epoch seems still undetected by current observations at z ≈ 6.

Cross-correlation of 21 cm and soft X-ray backgrounds during the epoch of reionization

The cross-correlation between the high-redshift 21 cm background and the Soft X-ray Background （SXB） of the Universe may provide an additional probe of the Epoch of Reionization. Here we use semi-numerical simulations to create 21 cm and soft X-ray intensity maps and construct their cross power spectra. Our results indicate that the cross power spectra are sensitive to the thermal and ionizing states of the intergalactic medium （IGM）. The 21 cm background correlates positively to the SXB on large scales during the early stages of the reionization. However as the reionization develops, these two back- grounds turn out to be anti-correlated with each other when more than - 15% of the IGM is ionized in a warm reionization scenario. The anti-correlated power reaches its maximum when the neutral fraction declines to 0.2-0.5. Hence, the trough in the cross power spectrum might be a useful tool for tracing the growth of HII regions during the middle and late stages of the reionization. We estimate the detectability of the cross power spectrum based on the abilities of the Square Kilometre Array and the Wide Field X-ray Telescope （WFXT）, and find that to detect the cross power spectrum, the pixel noise of X-ray images has to be at least 4 orders of magnitude lower than that of the WFXT deep survey.

Note on gauge invariance of second order cosmological perturbations

We study the gauge invariant cosmological perturbations up to the second order.We demonstrate that there are infinite families of gauge inv ariant variables at both the first and seco nd orders.The conversion formulae among different families are verified to be described by a finite number of bases that are gauge invariant.For the second order cosmological perturbations induced by the first order scalar perturbations,we explicitly represent their equations of motion in terms of the gauge invariant Newtonian,synchronous and hybrid variables,respectively.