In this talk, we revisit motivation from String Theory for new phases of cosmology – prior to inflation. Cosmic inflation offers a causal way to predict initial conditions for the growth of structure and density fluctuations in the cosmic microwave background and large scale structure formation. However, asymptotic deSitter space possesses a past cosmological (physical) singularity implying...
We discuss possible consequences of a manifestly non-commutative and T-duality covariant formulation of string theory on dark energy, when the correspondence between short distance (UV) and long distance (IR) physics is taken into account. We demonstrate that the dark energy is dynamical, time-dependent, and we compute the allowed values of w_{0} and w_{a} given by w(a)=w_{0}+(1-a)w_{a}, which...
We propose a simple, well-motivated, and robust model of slow-roll thawing quintessence, which is consistent with current observations of dark energy and naturally satisfies the conjectured swampland constraints.
The Lyman-alpha forest enables the study of cosmic structure on scales much smaller than those probed by baryon acoustic oscillations (BAO). While the BAO feature appears at 150 Mpc, the Lyman-alpha forest can resolve structure down to 1 Mpc, limited primarily by spectrograph resolution. This sensitivity makes it a powerful probe of small-scale clustering, which is influenced by the mass of...
The origin of large scale magnetic fields in the Universe is widely thought to be from early Universe processes, like inflation or phase transitions. These magnetic fields evolve via magnetohydrodynamic processes till the epoch of recombination. When structures begin to form in the later Universe, the conservation of magnetic flux amplifies the magnetic fields via the adiabatic collapse of...
Recently, the James Webb Space Telescope (JWST) has found early galaxies producing photons from more efficient ionization than previously assumed. This may suggest a reionization process with a larger reionization optical depth, $\tau_{reio}$, in some mild disagreement with that inferred from measurements of cosmic microwave background (CMB). Intriguingly, the CMB would prefer larger values of...
The long-standing discrepancy between late and early-time measurements of the Hubble parameter has given rise to a tension that has been resistant to a satisfactory theoretical explanation, even as the statistical tension has grown to about 4-6$\sigma$. In this work, we present a novel idea designed to alleviate this tension. Taking dark matter to consist of a population of primordial black...
We study the one-loop model of a pair of charged scalars with chemical potential mechanism in cosmological collider physics. We evaluate the one-loop amplitude analytically using spectral decomposition in de Sitter. Compared to previous analysis, our result predicts the correct power dependence on scalar masses and the chemical potential for both the signal and the background. Using these...
Stasis is a cosmological phenomena in which the abundances of the different energy components in the universe (such as matter, radiation, etc.) remain fixed for an extended period even though they are affected differently by expansion. Many of the mechanisms that lead to stasis revolve around a tower of states, which emerge in many BSM theories. In this talk, I will describe a realization of...
We analyse the formation criteria for PBH formation via the Israel-Junction conditions. We find that the usual overdensity condition is a weaker condition when compared to the more fundamental junction conditions. In addition, we look into the PBH formed in fermi-ball scenarios and compare it with known results in the literature.
Cosmological stasis is a phenomenon wherein the abundances of multiple cosmological energy components with different equations of state remain constant for an extended period despite the expansion of the universe. This stasis phenomenon can give rise to cosmological epochs in which the effective equation-of-state parameter $\langle w \rangle$ for the universe is constant, but differs from the...
The symmetry breaking of a scalar particle (axion-like particle) in the early Universe produces a rich cosmology. In this cosmology, different patches of the Universe with different energies are separated by a network of domain walls. When the Universe cools, the domain walls annihilate as the lowest-energy patches become dominant. The annihilation process ("catastrogenesis") produces...
Cosmological first order phase transitions proceed via the random nucleation and expansion of bubbles throughout space. This inherently stochastic process leads to statistical fluctuations across causally disconnected patches from which super-horizon curvature perturbations emerge. I will discuss how such phase transitions generate scalar perturbations that follow a universal power-law scaling...
Supercooled first-order phase transition (FOPT) can lead to the formation of primordial black holes (PBHs). This scenario imposes stringent requirements on the profile of the effective potential. In this work, we use the singlet extended Standard Model (xSM) as a benchmark model to investigate this possibility at the electroweak scale. The PBHs formed during a supercooled FOPT have a narrow...
Dark photons are dark massive vector gauge bosons that are one of the simplest extensions of the Standard Model. Through a kinetic mixing term, visible photons resonantly convert into dark photons when the plasma mass of an ionized gas is equal to the dark photon mass $m_{A'}$. This disappearance of Standard Model photons leaves a striking signature in a map of the 21-cm signal and enhances...
Future observations of the sky-averaged 21-cm signal during the cosmic dawn promise unprecedented measurements of the gas temperature in this epoch. Such measurements can place extremely strong constraints on the lifetime of dark matter. We revisit the projected bounds on minimal decaying dark matter scenarios and present new constraints for theoretically motivated non-minimal dark sectors,...
I will review the importance of Big-Bang Nucleosynthesis to cosmology and the search for new physics, and explain how to perform parameter inference with LINX, a fast and differentiable BBN code package.
We explore the big-bang nucleosynthesis (BBN) constraint on heavy neutrino that is a mixture of gauge singlet fermion and active neutrinos in the Standard Model. We work in the minimal model with only two parameters, the heavy neutrino mass $m_4$ and the mixing parameter $|U_{a4}|^2$, where $a=e$, $\mu$, or $\tau$ stands for the active neutrino flavor. We show that both the early universe...
In this talk, we look at some cosmological constraints on majoron dark matter in the singlet Majoron model. We consider two scenarios: pre-inflationary and post inflationary spontaneous lepton number symmetry breaking, while simultaneously demanding thermal leptogenesis to happen, and neutrino masses being generated by the type I seesaw mechanism. We derive the constraints and future prospects...
We discuss the Domain-Wall Standard Model formulated in five-dimensional spacetime. In this framework, all Standard Model (SM) particles are localized within a finite region (domain) along a non-compact extra spatial dimension. This scenario predicts the existence of a Nambu-Goldstone (NG) boson associated with the spontaneous violation of translational invariance in the extra dimension. The...
In models of warm dark matter, there is an appreciable population of high momentum particles in the early universe, which free stream out of primordial over/under densities, thereby prohibiting the growth of structure on small length scales. The distance that a dark matter particle travels without obstruction, known as the free streaming length, depends on the particle's mass and momentum, but...
I will discuss the possible imprints of high-scale non-thermal leptogenesis on cosmic microwave background (CMB) from the measurements of inflationary observables such as spectral index ($n_s$) and tensor-to-scalar (r) ratio, which otherwise is inaccessible to the conventional laboratory experiments. I will argue that non-thermal production of baryon (lepton) asymmetry from subsequent decays...
In this talk, I will present bounds on the variation of fundamental constants from the cosmic microwave background (CMB). In our theoretically motivated model, the variation is modulated by a scalar field that behaves as an ultralight dark matter (ULDM). We self-consistently compute the effects of the variation of constants on big bang nucleosynthesis (BBN) and propagate those effects to the...
Type-I seesaw scenario is arguably the simplest scenario to generate the observed neutrino oscillation data and the observed baryon asymmetry in the universe via leptogenesis. Based on the Casas–Ibarra general parametrization, we derive analytic expressions for the CP asymmetry parameter in the leptogenesis with two and three generations of right-handed Majorana neutrinos, reproducing the...
