Big bounce from spin and torsion

Four lectures on Big Bang cosmology, including microwave background radiation, Big Bang nucleosynthesis, dark matter, inflation, and baryogenesis.

The COSMOS survey is investigated for the presence of cosmic strings, indicated by observations of galaxy pairs that are consistent with the gravitational lensing signature of a cosmic string. Employing a new technique combining the simulation of cosmic strings at the catalog level and relying on the correlation and cross-correlation of galaxy pairs to deduce their morphological similarity, no evidence indicating the existence of straight and static cosmic strings is observed at tile position 55 of the COSMOS survey for a string with energy-density/relative-tilt of 5” and redshift of 1. Cosmic strings are hypothetical one-dimensional topological defects thought to have been formed in the early universe during the first fraction of a second after the Big Bang, as a result of phase transitions in different regions of spacetime. The existence of cosmic strings will undoubtedly provide solid evidence towards the understanding of the early universe, especially during the Planck epoch and earlier. Present theories about the early universe propose an intensely hot, dense and violent environment, whereby such a dense primordial soup of matter (the first matter to exist in the universe) underwent a series of phase transitions at high temperatures in different regions of spacetime present after the expansion from the singularity. 1 These phase transitions involve the breaking and restoration of symmetry, as described by quantum field theory. 2 The effects of high temperature should be accounted for, as a result of the early universe being very hot and dense immediately after the Big Bang. In this section, we shall consider the Abelian Higgs model 2 and assume that the cosmic strings formed are non-superconducting and local (i.e. the Lagrangian describing the energy density of the string is invariant under a symmetry transformation which may be different at every point), 1 and in addition take into account that the phase transitions are occurring in a radiationdominated FRW universe. 1 The early universe may be thought of as being in the symmetric phase when it was very hot and dense, with no strings being formed initially. However, when the

If gamma-ray bursts are at cosmological distances, they must be gravitationally lensed occasionally. The detection of lensed images with millisecond-to-second time delays provides evidence for intermediate-mass black holes, a population that has been difficult to observe. Several studies have searched for these delays in gamma-ray burst light curves, which would indicate an intervening gravitational lens. Among the $\sim 10^4$ gamma-ray bursts observed, there have been a handful of claimed lensing detections, but none have been statistically robust. Here we present a Bayesian analysis identifying gravitational lensing in the light curve of GRB950830. The inferred lens mass depends on the unknown lens redshift $z_l$, and is given by $(1+z_l)M_l = 5.5^{+1.7}_{-0.9}\times 10^4 $ M$_\odot$ (90% credibility), which we interpret as evidence for an intermediate-mass black hole. The most probable configuration, with a lens redshift $z_l\sim 1$ and a gamma-ray burst redshift $z_s\sim 2$, yields a present day number density of $n_\text{imbh}\approx 2.3^{+4.9}_{-1.6}\times10^{3} \text{ Mpc}^{-3}$ (90% credibility) with a dimensionless energy density $\Omega_\text{imbh} \approx 4.6^{+9.8}_{-3.3}\times10^{-4}$. The false alarm probability for this detection is $\sim0.6\%$ with trial factors. While it is possible that GRB950830 was lensed by a globular cluster, it is unlikely since we infer a cosmic density inconsistent with predictions for globular clusters $\Omega_\text{gc} \approx 8 \times 10^{-6}$ at 99.8% credibility. If a significant intermediate-mass black hole population exists, it could provide the seeds for the growth of supermassive black holes in the early Universe.

Extrapolating the present motion of expansion of the universe backward in time, we conclude that the early universe must have been very dense. And extrapolating the (adiabatic) expansion of the cosmic background radiation backward in time, we conclude that the early universe must have been very hot. Thus, at an early time, the universe must have been very different from what it is now. There were no stars and no galaxies, but only a uniform hot plasma, consisting of free electrons and free nuclei. The chemical composition of the early universe must also have been different. The heavy elements (that is, elements other than hydrogen, deuterium, helium, and lithium) in our immediate environment were formed by nuclear reactions in the cores of stars, so these elements did not exist in the early universe. At very early times, the violent thermal collisions would have prevented the existence of any kind of nuclei, and the matter in the universe must have been in the form of free electrons, protons, and neutrons. At the earliest times, even the protons and neutrons would have been disrupted, and the universe must have contained a mix of quarks, gluons, and other elementary particles.

In this paper, we show how one can find the Planck length multiplied by the speed of light, lpc, from a Newton force spring with no knowledge of the Newton gravitational constant G, the speed of light c, or the Planck constant h. This is remarkable, as for more than a hundred years, modern physics has assumed that one needs to know G, c, and the Planck constant in order to find any of the Planck units. We also show how to find other Planck units using the same method. To find the Planck time and the Planck length, one also needs to know the speed of light. To find the Planck mass and the Planck energy in their normal units, we need to know the Planck constant, something we will discuss in this paper. For these measurements, we do not need any knowledge of the Newton gravitational constant. It can be shown that the Planck length times the speed of light requires less information than any other Planck unit; in fact, it needs no knowledge of any fundamental constant to be measured. This is a revolutionary concept and strengthens the case for recent discoveries in quantum gravity theory completed by (Haug 2020 Phys. Essays 33 46–78).

Gamma-ray bursts (GRBs) are short and intense flashes at the cosmological distances, which are the most luminous explosions in the Universe. The high luminosities of GRBs make them detectable out to the edge of the visible universe. So, they are unique tools to probe the properties of high-redshift universe: including the cosmic expansion and dark energy, star formation rate, the reionization epoch and the metal evolution of the Universe. First, they can be used to constrain the history of cosmic acceleration and the evolution of dark energy in a redshift range hardly achievable by other cosmological probes. Second, long GRBs are believed to be formed by collapse of massive stars. So they can be used to derive the high-redshift star formation rate, which can not be probed by current observations. Moreover, the use of GRBs as cosmological tools could unveil the reionization history and metal evolution of the Universe, the intergalactic medium (IGM) properties and the nature of first stars in the early universe. But beyond that, the GRB high-energy photons can be applied to constrain Lorentz invariance violation (LIV) and to test Einstein's Equivalence Principle (EEP). In this paper, we review the progress on the GRB cosmology and fundamental physics probed by GRBs.

Long Gamma Ray Bursts (GRBs) constitute an important tool to study the Universe near and beyond the epoch of reionization. We delineate here the characteristics of an 'ideal' instrument for the search of GRBs at z>6-10. We find that the detection of these objects requires soft band detectors with a high sensitivity and moderately large FOV. In the light of these results, we compare available and planned GRB missions, deriving conservative predictions on the number of high-z GRBs detectable by these instruments along with the maximum accessible redshift. We show that the Swift satellite will be able to detect various GRBs at z>6, and likely at z>10 if the trigger threshold is decreased by a factor of ~2. Furthermore, we find that INTEGRAL and GLAST are not the best tool to detect bursts at z>6: the former being limited by the small FOV, and the latter by its hard energy band and relatively low sensitivity. Finally, future missions (SVOM, EDGE, but in particular EXIST) will provide a good sample of GRBs at z>6 in a few years of operation.

We discuss the quantum dynamics of the Dirac fermion particle in a gauge gravitational field. The minimal as well as the Pauli-type nonminimal coupling of a fermion with external fields is studied, bringing into consideration the notions of the translational and the Lorentz gravitational moments. The anomalous gravitomagnetic and gravitoelectric moments are ruled out on the basis of the covariance arguments. We derive the general Foldy-Wouthuysen transformation for an arbitrary configuration of the gauge gravitational field without assuming it weak. Making use of the Foldy-Wouthuysen Hamiltonian for the Dirac particle coupled to magnetic field in a noninertial reference system, we analyze the recent experimental data and obtain bounds on the spacetime torsion.

Fred Hoyle, who passed away on 20 August 2001, was one of the most important figures in 20th century physics and astronomy. He is most famous for coining the term 'Big Bang' in a BBC radio broadcast in 1950, even though the fact that his comment was an insult seems to have been lost in time. He left behind a lasting body of work, foremost of which is his work with Willy Fowler and the Burbidges on the origin of the chemical elements in the 1950s. Sir Martin Rees, Astronomer Royal and Professor at the Institute of Astronomy in Cambridge, speaking to Physics Education said 'Hoyle was a great astrophysicist, who from 1945 to 1970 contributed more good creative ideas than anyone else in the world.'

In chameleon gravity, there exists a light scalar field that couples to the trace of the stress-energy tensor in such a way that its mass depends on the ambient matter density, and the field is screened in local, high-density environments. Recently it was shown that, for the runaway potentials commonly considered in chameleon theories, the field's coupling to matter and the hierarchy of scales between Standard Model particles and the energy scale of such potentials result in catastrophic effects in the early Universe when these particles become nonrelativistic. Perturbations with trans-Planckian energies are excited, and the theory suffers a breakdown in calculability at the relatively low temperatures of Big Bang Nucleosynthesis. We consider a chameleon field in a quartic potential and show that the scale-free nature of this potential allows the chameleon to avoid many of the problems encountered by runaway potentials. Following inflation, the chameleon field oscillates around the minimum of its effective potential, and rapid changes in its effective mass excite perturbations via quantum particle production. The quartic model, however, only generates high-energy perturbations at comparably high temperatures and is able remain a well-behaved effective field theory at nucleosynthesis.

We present an expanding, spatially flat ($k=0$) FLRW quantum spacetime with a Big Bang, considered as a background in Yang-Mills matrix models. The FLRW geometry emerges in the semi-classical limit as a projection from the fuzzy hyperboloid. We analyze the propagation of scalar fields, and demonstrate that their Feynman propagator resembles the Minkowski space Feynman propagator in the semi-classical regime. Moreover, the higher spin modes predicted by the matrix model are described explicitly. These results are compared to recent results on $k=-1$ FLRW quantum spacetimes with a Big Bounce.

Heavy long-lived particles are abundant in BSM physics and will, under generic circumstances, get to dominate the energy density of the universe. The resulting matter dominated era has to end through the decay of the heavy matter component particles of mass M, and before the universe cools down to a temperature of a few MeV, in order not to upset the successful predictions of Big Bang Nucleosynthesis. The process of thermalization of their decay products, of initial energy ∼ M/2, into a thermal bath of temperature T primarily involves near-collinear splittings of energetic particles into two particles with lower energy. The correct treatment of these processes requires the inclusion of coherence effects which suppress the splitting rate. We write down and numerically solve the resulting coupled Boltzmann equations including all gauge bosons and fermions of the unbroken phase of the Standard Model (SM). We then comment on the dependence of the nonthermal spectra on the ratio M/T, as well as on the matter decay rate and branching ratios into various SM particles.

One of the greatest problems of primordial inflation is that the inflationary space-time is past-incomplete. This is mainly because Einstein's GR suffers from a space-like Big Bang singularity. It has recently been shown that ghost-free, non-local higher-derivative ultra-violet modifications of Einstein's gravity may be able to resolve the cosmological Big Bang singularity via a non-singular bounce. Within the framework of such non-local cosmological models, we are going to study both sub- and super-Hubble perturbations around an inflationary trajectory which is preceded by the Big Bounce in the past, and demonstrate that the inflationary trajectory has an ultra-violet completion and that perturbations do not suffer from any pathologies.

The imprint of acoustic waves in the temperature fluctuations of the cosmic background radiation had its origin in the distribution of matter just prior to recombination. Could the same pattern be seen directly in the distribution of galaxies in the present-day universe? Further galaxy redshift surveys revealed more astonishing structures—great walls of galaxies and empty voids that came to be known as the ‘cosmic web’. Correlations in the separation distances of these galaxies revealed the pattern expected from what was now ‘standard’ Big Bang cosmology. They placed the sound horizon at about 470 million light-years. The WMAP mission was extended to 2008, bringing the Hubble constant to 70.5 km/s/Mpc with an error of less than 2%. Adam Riess, who had been part of the High-Z Supernova Search Team and was awarded a share of the 2011 Nobel physics prize, judged that it was necessary to refine further the distance ladder to provide similarly precise direct measurements of the Hubble constant. He proposed studying Cepheid variables in galaxies that are also host to Type Ia supernovae. But from about 2009 the determinations began to part company. ‘Early-universe’ predictions for the Hubble constant based on big bang cosmology have yielded estimates between 67 and 68 km/s/Mpc, with errors less than 2%. However, ‘late-universe’ measurements yield values more like 73 km/s/Mpc, with similar error. The universe appears to be expanding faster than predicted by analyses of acoustic oscillations from the early universe. This is the Hubble tension.

A field theory is proposed where the regular fermionic matter and the dark fermionic matter can be different states of the same "primordial" fermion fields. In regime of the fermion densities typical for normal particle physics, the primordial fermions split into three families identified with regular fermions. When fermion energy density becomes comparable with dark energy density, the theory allows transition to new type of states. The possibility of such Cosmo-Low Energy Physics (CLEP) states is demonstrated by means of solutions of the field theory equations describing FRW universe filled with homogeneous scalar field and uniformly distributed nonrelativistic neutrinos. Neutrinos in CLEP state are drawn into cosmological expansion by means of dynamically changing their own parameters. One of the features of the fermions in CLEP state is that in the late time universe their masses increase as a3/2 (a=a(t) is the scale factor). The energy density of the cold dark matter consisting of neutrinos in CLEP state scales as a sort of dark energy; this cold dark matter possesses negative pressure and for the late time universe its equation of state approaches that of the cosmological constant. The total energy density of such universe is less than it would be in the universe free of fermionic matter at all.