Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userCosmological Constraints on Light (but Massive) Relics
74
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
Many scenarios of physics beyond the standard model predict new light, weakly coupled degrees of freedom, populated in the early universe and remaining as cosmic relics today. Due to their high abundances, these relics can significantly affect the evolution of the universe. For instance, massless relics produce a shift $Delta N_{rm eff}$ to the cosmic expectation of the effective number of active neutrinos. Massive relics, on the other hand, additionally become part of the cosmological dark matter in the later universe, though their light nature allows them to freely stream out of potential wells. This produces novel signatures in the large-scale structure (LSS) of the universe, suppressing matter fluctuations at small scales. We present the first general search for such light (but massive) relics (LiMRs) with cosmic microwave background (CMB) and LSS data, scanning the 2D parameter space of their masses $m_X$ and temperatures $T_X^{(0)}$ today. In the conservative minimum-temperature ($T_X^{(0)}=0.91$ K) scenario, we rule out Weyl (and higher-spin) fermions -- such as the gravitino -- with $m_Xgeq 2.26$ eV at 95% C.L., and set analogous limits of $m_Xleq 11.2, 1.06, 1.56$ eV for scalar, vector, and Dirac-fermion relics. This is the first search for LiMRs with joint CMB, weak-lensing, and full-shape galaxy data; we demonstrate that weak-lensing data is critical for breaking parameter degeneracies, while full-shape information presents a significant boost in constraining power relative to analyses with only baryon acoustic oscillation parameters. Under the combined strength of these datasets, our constraints are the tightest and most comprehensive to date.
rate research
Read More
Cosmological data provide a powerful tool in the search for physics beyond the Standard Model (SM). An interesting target are light relics, new degrees of freedom which decoupled from the SM while relativistic. Nearly massless relics contribute to the radiation energy budget, and are commonly parametrized as variations in the effective number $N_{rm eff}$ of neutrino species. Additionally, relics with masses greater than $10^{-4}$ eV become non-relativistic before today, and thus behave as matter instead of radiation. This leaves an imprint in the clustering of the large-scale structure of the universe, as light relics have important streaming motions, mirroring the case of massive neutrinos. Here we forecast how well current and upcoming cosmological surveys can probe light massive relics (LiMRs). We consider minimal extensions to the SM by both fermionic and bosonic relic degrees of freedom. By combining current and upcoming cosmic-microwave-background and large-scale-structure surveys, we forecast the significance at which each LiMR, with different masses and temperatures, can be detected. We find that a very large coverage of parameter space will be attainable by upcoming experiments, opening the possibility of exploring uncharted territory for new physics beyond the SM.
Axions, if realized in nature, can be copiously produced in the early universe via thermal processes, contributing to the mass-energy density of thermal hot relics. In light of the most recent cosmological observations, we analyze two different thermal processes within a realistic mixed hot-dark-matter scenario which includes also massive neutrinos. Considering the axion-gluon thermalization channel we derive our most constraining bounds on the hot relic masses $m_a < 7.46$ eV and $sum m_ u< 0.114$ eV both at 95 per cent CL; while studying the axion-pion scattering, without assuming any specific model for the axion-pion interactions and remaining in the range of validity of the chiral perturbation theory, our most constraining bounds are improved to $m_a<0.91$ eV and $sum m_ u< 0.105$ eV, both at 95 per cent CL. Interestingly, in both cases, the total neutrino mass lies very close to the inverted neutrino mass ordering prediction. If future terrestrial double beta decay and/or long baseline neutrino experiments find that the nature mass ordering is the inverted one, this could rule out a wide region in the currently allowed thermal axion window. Our results therefore strongly support multi-messenger searches of axions and neutrino properties, together with joint analyses of their expected sensitivities.
If active neutrinos undergo non-standard (`secret) interactions (NS$ u$I) the cosmological evolution of the neutrino fluid might be altered, leaving an imprint in cosmological observables. We use the latest publicly available CMB data from Planck to constrain NS$ u$I inducing $ u- u$ scattering, under the assumption that the mediator $phi$ of the secret interaction is very light. We find that the effective coupling constant of the interaction, $g_mathrm{eff}^4 equiv langle sigma vrangle T_ u^2$, is constrained at $< 2.35times10^{-27}$ (95% credible interval), which stregthens to $g_mathrm{eff}^4 < 1.64times10^{-27}$ when Planck non-baseline small-scale polarization is considered. Our findings imply that after decoupling at $Tsimeq 1$ MeV, cosmic neutrinos are free streaming at redshifts $z>3800$, or $z>2300$ if small-scale polarization is included. These bounds are only marginally improved when data from geometrical expansion probes are included in the analysis to complement Planck. We also find that the tensions between CMB and low-redshift measurements of the expansion rate $H_0$ and the amplitude of matter fluctuations $sigma_8$ are not significantly reduced. Our results are independent on the underlying particle physics model as long as $phi$ is very light. Considering a model with Majorana neutrinos and a pseudoscalar mediator we find that the coupling constant $g$ of the secret interaction is constrained at $lesssim 7times 10^{-7}$. By further assuming that the pseudoscalar interaction comes from a dynamical realization of the see-saw mechanism, as in Majoron models, we can bound the scale of lepton number breaking $v_sigma$ as $gtrsim (1.4times 10^{6})m_ u$.
We revise the cosmological phenomenology of Macroscopic Dark Matter (MDM) candidates, also commonly dubbed as Macros. A possible signature of MDM is the capture of baryons from the cosmological plasma in the pre-recombination epoch, with the consequent injection of high-energy photons in the baryon-photon plasma. By keeping a phenomenological approach, we consider two broad classes of MDM in which Macros are composed either of ordinary matter or antimatter. In both scenarios, we also analyze the impact of a non-vanishing electric charge carried by Macros. We derive constraints on the Macro parameter space from three cosmological processes: the change in the baryon density between the end of the Big Bang Nucleosynthesis (BBN) and the Cosmic Microwave Background (CMB) decoupling, the production of spectral distortions in the CMB and the kinetic coupling between charged MDM and baryons at the time of recombination. In the case of neutral Macros we find that the tightest constraints are set by the baryon density condition in most of the parameter space. For Macros composed of ordinary matter and with binding energy $I$, this leads to the following bound on the reduced cross-section: $sigma_X/M_X lesssim 6.8 cdot 10^{-7} left(I/mathrm{MeV}right)^{-1.56} , text{cm}^2 , text{g}^{-1}$. Charged Macros with surface potential $V_X$, instead, are mainly constrained by the tight coupling with baryons, resulting in $sigma_X/M_X lesssim 2 cdot 10^{-11} left(|V_X|/mathrm{MeV}right)^{-2} text{cm}^2 , text{g}^{-1}$. Finally, we show that future CMB spectral distortions experiments, like PIXIE and SuperPIXIE, would have the sensitivity to probe larger regions of the parameter space: this would allow either for a possible evidence or for an improvement of the current bounds on Macros as dark matter candidates.
The increasingly significant tensions within $Lambda$CDM, combined with the lack of detection of dark matter (DM) in laboratory experiments, have boosted interest in non-minimal dark sectors, which are theoretically well-motivated and inspire new search strategies for DM. Here we consider, for the first time, the possibility of DM having simultaneous interactions with photons, baryons, and dark radiation (DR). We have developed a new and efficient version of the Boltzmann code CLASS that allows for one DM species to have multiple interaction channels. With this framework we reassess existing cosmological bounds on the various interaction coefficients in multi-interacting DM scenarios. We find no clear degeneracies between these different interactions and show that their cosmological effects are largely additive. We further investigate the possibility of these models to alleviate the cosmological tensions, and find that the combination of DM-photon and DM-DR interactions can at the same time reduce the $S_8$ tension (from $2.3sigma$ to $1.2sigma$) and the $H_0$ tension (from $4.3sigma$ to $3.1sigma$). The public release of our code will pave the way for the study of various rich dark sectors.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
