Conveners
Cosmology & Dark Energy: BAO review, Dark Radiation, Millicharge
- Fazlollah Hajkarim (University of Oklahoma)
Cosmology & Dark Energy: Anomalies and Baryogenesis
- Michael Shamma (TRIUMF)
Cosmology & Dark Energy: Eary Universe and Stasis
- Taewook Youn (Cornell University)
Cosmology & Dark Energy: CMB and other observations
- Keisuke Inomata (Jonhs Hopkins University)
Cosmology & Dark Energy: Early Universe
- Subhajit Ghosh (The University of Texas at Austin)
Baryon Acoustic Oscillations are considered one of the most powerful cosmological probes. They are assumed to provide distance measures independent of a specific cosmological model. At the same time the obtained distances are considered agnostic with respect to other cosmological observations. However, in current measurements, the inference is done assuming parameter values of a fiducial LCDM...
Models of cosmology including dark radiation (DR) have garnered recent interest, due in part to their versatility in modifying the $\Lambda$CDM concordance model in hopes of resolving observational tensions. Equally interesting is the capacity for DR models to be constrained or detected with current and near-term cosmological data. Finally, DR models have the potential to be embedded into...
Cosmological first order phase transitions are typically associated with physics beyond the Standard Model, and thus of great theoretical and observational interest. Models of phase transitions where the energy is mostly converted to dark radiation can be constrained through limits on the dark radiation energy density (parameterized by $\Delta N_{\rm eff}$). However, the current constraint...
We demonstrate that the searches for dark sector particles can provide probes of reheating scenarios, focusing on the cosmic millicharge background produced in the early universe. We discuss two types of millicharge particles (mCPs): either with, or without, an accompanying dark photon. These two types of mCPs have distinct theoretical motivations and cosmological signatures. We discuss...
The โHubble tensionโ refers to a disagreement between the present expansion rate of the universe, and that projected by applying our current model (โLambda Cold Dark Matterโ or Lambda-CDM) to early universe measurements; Lambda-CDM yields an expansion rate substantially different from current measurement, by more than five standard deviations. We describe the model, in particular the meaning...
Cosmological observables are particularly sensitive to key ratios of energy densities and rates, both today and at earlier epochs of the Universe. Well-known examples include the photon-to-baryon and the matter-to-radiation ratios. Equally important, though less publicized, are the ratios of pressure-supported to pressureless matter and the Thomson scattering rate to the Hubble rate around...
With the growing precision of cosmological measurements, tensions in the determination of cosmological parameters have arisen that might be the first manifestations of physics going beyond $\Lambda$CDM. We propose a new class of interacting dark sector models, which lead to qualitatively distinct cosmological behavior, dark acoustic oscillation, which can potentially simultaneously address the...
Phase transitions provide a useful mechanism to produce both electroweak baryogenesis (EWBG) and gravitational waves (GW). We propose a left-right symmetric model with two Higgs doublets, a left-handed doublet $H_L$ and a right-handed doublet $H_R$, and a scalar singlet $\sigma$ under a $H_L \leftrightarrow H_R$ and $\sigma \leftrightarrow -\sigma$ symmetry as discussed by Gu. We utilize a...
We propose a novel framework where baryon asymmetry of the universe can arise due to forbidden decay of dark matter (DM) enabled by finite-temperature effects in the vicinity of a first order phase transition (FOPT). In order to implement this novel cogenesis mechanism, we consider the extension of the standard model by one scalar doublet $\eta$, three right handed neutrinos (RHN), all odd...
We calculate the effects of a light, very weakly-coupled boson $X$ arising from a spontaneously broken $U(1)_{B-L}$ symmetry on $\Delta N_{\rm eff}$ as measured by the CMB and $Y_p$ from BBN. Our focus is the mass range $1 \; {\rm eV} \, \lesssim m_X \lesssim 100 \; {\rm MeV}$. We find $U(1)_{B-L}$ is more strongly constrained by $\Delta N_{\rm eff}$ than previously considered. While some of...
It has recently been realized that many extensions of the Standard Model give rise to cosmological histories exhibiting extended epochs of cosmological stasis โ epochs wherein the abundances of multiple energy components (such as matter, radiation, or vacuum energy) remain effectively constant despite cosmological expansion. In this talk, I shall discuss a novel realization of stasis...
Cosmological stasis is a phenomenon in which multiple energy components in the universe (such as matter, radiation, or vacuum energy) maintain constant abundances despite cosmological expansion. Such epochs have recently been shown to arise naturally in cosmologies associated with numerous extensions of the Standard Model, and can persist across many e-folds of expansion. In this talk, I...
Recently, it has been shown that there can exist a type of cosmological epoch in which the abundances of different energy components remain essentially fixed for an extended period. This phenomenon, which is known as cosmic stasis, has been shown to arise in a variety of BSM contexts. In all previous realizations of stasis, however, the sustained transfer of energy density between energy...
Cosmological collider physics, a mechanism in which heavy particles produced during inflation leave an observable footprint in primordial non Guassianities, carries the prospect of probing physics at scales far higher than any terrestrial collider. Supersymmetric grand unified theories (SUSY GUTs) are a highly motivated target, but the high unification scale is orders of magnitude above the...
The string theory axions can naturally form stable string-domain wall network. The later collapse of the domain walls produce more than one type of axion mass eigenstates apart from gravitational waves.
We propose a solution to the strong CP problem that specifically relies on massless quarks and has no light axion. The QCD color group $SU(3)_c$ is embedded into a larger, simple gauge group (grand-color) where one of the massless, colored fermions enjoys an anomalous chiral symmetry, rendering the strong CP phase unphysical. The grand-color gauge group $G_{\rm GC}$ is Higgsed down to...
In this talk I will present forecasts on cosmological parameters for a CMB-HD survey. These forecasts include residual foregrounds, delensing of the acoustic peaks, and DESI BAO. We find that CMB-HD can improve constraints on the scalar spectral index, n_s, by a factor of two compared to precursor surveys. We also find that the CMB-HD constraint on N_eff can rule out light thermal particles...
The primary two methods for measuring the Hubble constant โ forward modeling of CMB fluctuations and distance ladder measurements โ disagree at a level that is statistically significant. A third method, known as the bright standard siren method, could add another competitive measurement to the fray, potentially pointing to a resolution of the aforementioned tension. This direct method...
The peaks of the CMB spectra provide a direct cosmological probe for studying dark sector physics. Specifically, a shift in the peak positions corresponds to a phase shift in the acoustic oscillations of the photon-baryon plasma before recombination, which is sensitive to the propagation behavior of non-photon radiation. It has been established that CMB spectra shift to higher l-modes if the...
Gravitational lensing of the cosmic microwave background (CMB) encodes information from the low-redshift universe. Therefore, its measurement is useful for constraining cosmological parameters that describe structure formation, e.g. matter density ($\Omega_m$), the amplitude of clustering ($\sigma_8$), and the sum of neutrino masses. In this talk, I will first present cosmological results from...
Even if they do not comprise the dark matter, light axion-like particles may be sourced by bulk Standard Model matter through a coupling that violates CP. When considered in combination with the usual axion-photon coupling, the resulting 'monopole-dipole' scenario possesses a rich phenomenology, as has previously been studied in the context of terrestrial detection. In this talk, I discuss the...
We study the impact of an early dark energy component (EDE) present during big bang nucleosynthesis (BBN) on the elemental abundances of deuterium (D/H), and helium ($Y_p$), as well as the effective relativistic degrees of freedom $N_{\rm eff}$. We consider a simple model of EDE that is constant up to a critical temperature. After the critical temperature, the EDE decays as either standard...
The scalar and tensor fluctuations produced during inflation can be correlated, if arising from the same underlying mechanism. We investigate such correlation in the model of axion inflation, where the rolling inflaton produces quanta of a $U(1)$ gauge field which, in turn, source scalar and tensor fluctuations. We compute the primordial correlator of the curvature perturbation, $\zeta$, with...
A thermal interpretation of the stochastic formalism of a slow-rolling scalar field in a de Sitter (dS) universe is given. We construct a correspondence between causal patches in the 3-dimensional space of a dS universe and particles living in an abstract space. By assuming a dual description of scalar fields and classical mechanics in the abstract space, we show that the stochastic evolution...
The interplay between cosmology and strongly coupled dynamics can yield transient features that vanish at late times of cosmic evolution, but which may leave behind phenomenological signatures in the spectrum of primordial fluctuations and cosmological observables. Of particular interest are strongly coupled extensions of the standard model featuring approximate conformal invariance. In flat...
If enough primordial black holes (PBH) are produced in the early Universe, they can come to dominate its energy density. This is usually considered viable as long as the PBHs evaporate and reheat the universe above the temperature needed for Big Bang nucleosynthesis, which requires $m_\mathrm{BH} \lesssim 10^9$ g. However, during this period of early matter domination, perturbations can grow...
I examine one-loop corrections from small-scale curvature perturbations to the superhorizon-limit ones in single-field inflation models, which have recently caused controversy. I consider the case where the Universe experiences transitions of slow-roll (SR) โ intermediate period โ SR. The intermediate period can be an ultra-slow-roll period or a resonant amplification period, either of which...
Cosmic microwave background anisotropies have proven to be the most powerful probe of non-trivial topology of the Universe. Within ฮCDM, these anisotropies have well-characterized statistical properties, the signal is principally from a thin spherical shell centered on the observer (the last scattering surface). The most generic signature of cosmic topology in the microwave background is pairs...
We demonstrate that the searches for dark sector particles can provide probes of reheating scenarios, focusing on the cosmic millicharge background produced in the early universe. We discuss two types of millicharge particles (mCPs): either with, or without, an accompanying dark photon. These two types of mCPs have distinct theoretical motivations and cosmological signatures. We discuss...
