Detection of early-universe gravitational-wave signatures and fundamental physics

Detection of a gravitational-wave signal of non-astrophysical origin would be a landmark discovery, potentially providing a significant clue to some of our most basic, big-picture scientific questions about the Universe. In this white paper, we survey the leading early-Universe mechanisms that may produce a detectable signal-including inflation, phase transitions, topological defects, as well as primordial black holes-and highlight the connections to fundamental physics. We review the complementarity with collider searches for new physics, and multimessenger probes of the large-scale structure of the Universe.

Viable Requirements of Curvature Coupling Helical Magnetogenesis Scenario

In the present work, we examine the following points in the context of curvature coupling helical magnetogenesis scenario where the electromagnetic field couples with the background Ricci scalar as well as with the background Gauss-Bonnet cuvature term: (1) whether the model is consistent with the predictions of perturbative quantum field theory (QFT) and (2) whether the curvature perturbation induced by the generated electromagnetic (EM) field during inflation is consistent with the Planck data. Such requirements are well motivated in order to argue for the viability of the magnetogenesis model under consideration. In fact, our recently proposed helical magnetogenesis scenario seems to predict sufficient magnetic strength over large scales and also leads to the correct baryon asymmetry of the universe for a suitable range of the model parameter. However in the realm of inflationary magnetogenesis, these requirements are not enough to argue for the viability of the model; in particular, one needs to examine some more important requirements in this regard. We may recall that the calculations generally used to determine the magnetic field’s power spectrum are based on the perturbative QFT; therefore, it is important to examine whether the predictions of such perturbative QFT are consistent with the observational bounds of the model parameter. On other hand, the generated gauge field acts as a source of the curvature perturbation which needs to be suppressed compared to that contributed from the inflaton field in order to be consistent with the Planck observation. For the perturbative requirement, we examine whether the condition SCBScan<1 is satisfied, where SCB and Scan are the non-minimal and the canonical action of the EM field, respectively. Moreover, we determine the power spectrum of the curvature perturbation sourced by the EM field during inflation and evaluate necessary constraints in order to be consistent with the Planck data. Interestingly, both the aforementioned requirements in the context of the curvature coupling helical magnetogenesis scenario are found to be simultaneously satisfied by that range of the model parameter which leads to the correct magnetic strength over the large scale modes.

Topics in Cosmology—Clearly Explained by Means of Simple Examples

This is a very comprehensible review of some key issues in modern cosmology. Simple mathematical examples and analogies are used, whenever available. The starting point is the well-known Big Bang cosmology (BBC). We deal with the mathematical singularities appearing in this theory and discuss some ways to remove them. Next, and before introducing the inflationary paradigm by means of clear examples, we review the horizon and flatness problems of the old BBC model. We then consider the current cosmic acceleration and, as a procedure to deal with both periods of cosmic acceleration in a unified way, we study quintessential inflation. Finally, the reheating stage of the universe via gravitational particle production, which took place after inflation ended, is discussed in clear mathematical terms, by involving the so-called α-attractors in the context of quintessential inflation.