Minihalos as probes of the inflationary spectrum: accurate boost factor calculation and new CMB constraints

Although the spectrum of primordial fluctuations has been accurately measured on scales above $\sim 0.1~\rm{Mpc}$, only upper limits exist on smaller scales. In this study, we investigate generic monochromatic enhancements to the $\Lambda$CDM spectrum that trigger the collapse of ultracompact minihalos (UCMHs) well before standard structure formation. We refine previous treatments by considering a mixed population of halos with different density profiles, that should realistically arise as a consequence of late-time accretion and mergers. Assuming that dark matter (DM) can self-annihilate, we find, as expected, that UCMHs can greatly enhance the annihilation rate around recombination, significantly imprinting the cosmic microwave background (CMB) anisotropies. However, we provide additional insight on the theoretical uncertainties that currently impact that boost and which may affect late-time probes such as the 21 cm line or $\gamma$-ray signals. We derive constraints on the primordial power spectrum on small scales using the ExoCLASS/HYREC codes and the Planck legacy data. We account for the velocity dependence of the DM annihilation cross-section ($s$- or $p$-wave), annihilation channel, the DM particle mass and the inclusion of late-time halo mergers. Our $s$-wave constraints are competitive with previous literature, excluding primordial amplitudes $A_{\star} \gtrsim 10^{-6.5}$ at wavenumbers $k \sim 10^4-10^7 \ \rm{Mpc}^{-1}$. For the first time, we highlight that even$p$-wave processes have constraining power on the primordial spectrum for cross-sections still allowed by currently the strongest astrophysical constraints. Finally, we provide an up-to-date compilation of the most stringent limits on the primordial power spectrum across a wide range of scales.Comment: 26+18 pages, 12 figures. Added citations and reshaped the appendices. v2 matches the published JCAP version. Comments welcome

Probing Early Modification of Gravity with Planck, ACT and SPT

We consider a model of early modified gravity (EMG) that was recently proposed as a candidate to resolve the Hubble tension. The model consists in a scalar field $\sigma$ with a non-minimal coupling (NMC) to the Ricci curvature of the form $F(\sigma) = M_{\mathrm{pl}}^2+\xi\sigma^2$ and an effective mass induced by a quartic potential $V(\sigma) = \lambda \sigma^4/4$. We present the first analyses of the EMG model in light of the latest ACT DR4 and SPT-3G data in combination with full Planck data, and find a $\gtrsim 2\sigma$ preference for a non-zero EMG contribution from a combination of primary CMB data alone, mostly driven by ACT DR4 data. This is different from popular 'Early Dark Energy' models, which are detected only when the high-$\ell$ information from Planck temperature is removed. We find that the NMC plays a key role in controlling the evolution of density perturbations that is favored by the data over the minimally coupled case. Including measurements of supernovae luminosity distance from Pantheon+, baryonic acoustic oscillations and growth factor from BOSS, and CMB lensing of Planck leaves the preference unaffected. In the EMG model, the tension with S$H_0$ES is alleviated from $\sim 6\sigma$ to $\sim 3\sigma$. Further adding S$H_0$ES data rise the detection of the EMG model above $5\sigma$.Comment: 25 pages, 9 figures, 5 tables. Comments welcome

The weak, the strong and the ugly -- A comparative analysis of interacting stepped dark radiation

Models which address both the Hubble and $S_8$ tensions with the same mechanism generically cause a pre-recombination suppression of the small scale matter power spectrum. Here we focus on two such models. Both models introduce a self-interacting dark radiation fluid scattering with dark matter, which has a step in its abundance around some transition redshift. In one model, the interaction is weak and with all of the dark matter whereas in the other it is strong but with only a fraction of the dark matter. The weakly interacting case is able to address both tensions simultaneously and provide a good fit to a the Planck measurements of the cosmic microwave background (CMB), the Pantheon Type Ia supernovae, and a combination of low and high redshift baryon acoustic oscillation data, whereas the strongly interacting model cannot significantly ease both tensions simultaneously. The addition of high-resolution cosmic microwave background (CMB) measurements (ACT DR4 and SPT-3G) slightly limits both model's ability to address the Hubble tension. The use of the effective field theory of large-scale structures analysis of BOSS DR12 LRG and eBOSS DR16 QSO data additionally limits their ability to address the $S_8$ tension. We explore how these models respond to these data sets in detail in order to draw general conclusions about what is required for a mechanism to address both tensions. We find that in order to fit the CMB data the time dependence of the suppression of the matter power spectrum plays a central role.Comment: 22 pages, 17 figures, 5 tables. Any comment is welcome

Third EuCAPT Annual Symposium

Although the CMB and galaxy surveys provide precise measurements of the primordial power spectrum at large scales, the small-scale power spectrum remains largely unconstrained. An enhancement in the small-scale primordial spectrum can lead to the formation of Ultra-Compact-Mini-Halos (UCMH) much earlier than standard halo can form. As a result, the DM annihilation signal receives a boost than can strongly impact the CMB power spectra. In this talk, I briefly discuss how to model the effect of s- and p-wave annihilations in UCMHs onto the CMB. I quantify the impact of late-time halo mergers using excursion set theory, and argue that the associated uncertainty in the boost of energy injection is limited for the CMB, but can have serious consequences for late time probes (i.e. for the 21-cm signal). Finally, I demonstrate that the derived CMB constraints on the amplitude of the small-scale spectrum are competitive with those coming from gamma-ray observations, even for p-wave processes

A step in the right direction? Analyzing the Wess Zumino Dark Radiation solution to the Hubble tension

The Wess Zumino Dark Radiation (WZDR) model first proposed in arXiv:2111.00014 shows great promise as a well-motivated simple explanation of the Hubble tension between local and CMB-based measurements. In this work we investigate the assumptions made in the original proposal and confront the model with additional independent data sets. We show that the original assumptions can have an impact on the overall results but are usually well motivated. We further demonstrate that the preference for negative $\Omega_k$ remains at a similar level as for the $\Lambda$CDM model, while the $A_L$ tension is slightly increased. Furthermore, the tension between Planck data for $\ell < 800$ and $\ell \geq 800$ is significantly reduced for the WZDR model. The independent data sets show slightly more permissive bounds on the Hubble parameter, allowing the tension to be further reduced to $2.1 \sigma$ (CMB-independent) or $1.9\sigma$ (ACT+WMAP). However, no combination shows a large preference for the presence of WZDR. We also investigate whether additional dark radiation -- dark matter interactions can help in easing the $S_8$ tension as well. Assuming all of the dark matter to be interacting and a temperature-independent scattering rate, we find that the CMB data are too restrictive on this additional component as to allow a significant decrease in the clustering

Early dark energy resolution to the Hubble tension in light of weak lensing surveys and lensing anomalies

International audienceA constant early dark energy (EDE) component contributing a fraction fEDE(zc)∼10% of the energy density of the universe around zc≃3500 and diluting as or faster than radiation afterwards, can provide a simple resolution to the Hubble tension, the ∼5σ discrepancy—in the ΛCDM context—between the H0 value derived from early- and late-universe observations. However, it has been pointed out that including Large-Scale Structure (LSS) data, which are in ∼3σ tension with ΛCDM and EDE cosmologies, might break some parameter degeneracy and alter these conclusions. We reassess the viability of the EDE against a host of high- and low-redshift measurements, by combining LSS observations from recent weak lensing (WL) surveys with CMB, baryon acoustic oscillation (BAO), growth function (FS) and Supernova Ia (SNIa) data. Introducing a model whose only parameter is fEDE(zc), we report in agreement with past work a ∼2σ preference for nonzero fEDE(zc) from Planck CMB data alone, while the tension with the local H0 measurement from sh0es is reduced below 2σ. Adding BAO, FS and SNIa does not affect this conclusion, while the inclusion of a prior on H0 from sh0es increase the preference for EDE over ΛCDM to the ∼3.6σ level. After checking the EDE nonlinear matter power spectrum as predicted by standard semi-analytical algorithms via a dedicated set of N-body simulations, we test the 1-parameter EDE cosmology against WL data. We find that it does not significantly worsen the fit to the S8 measurement as compared to ΛCDM, and that current WL observations do not exclude the EDE resolution to the Hubble tension. We also caution against the interpretation of constraints obtained from combining statistically inconsistent datasets within the ΛCDM cosmology. In light of the CMB lensing anomalies, we show that the lensing-marginalized CMB data also favor nonzero fEDE(zc) at ∼2σ, predicts H0 in 1.4σ agreement with sh0es and S8 in 1.5σ and 0.8σ agreement with kids-viking and des respectively. There still exists however a ∼2.5σ tension with the joint results from kids-viking and des. With an eye on Occam’s razor, we finally discuss promising extensions of the EDE cosmology that could allow us to fully restore cosmological concordance

Linear cosmological constraints on two-body decaying dark matter scenarios and the S8 tension

International audienceThe “S8 tension” is a long-standing discrepancy between the cosmic microwave background (CMB) and weak gravitational lensing determination of the amplitude of matter fluctuations, parametrized as S8≡σ8(Ωm/0.3)0.5, where σ8 is the root-mean-square of matter fluctuations on an 8  h-1 Mpc scale, and Ωm is the total matter abundance. It was recently shown that dark matter (DM) decaying into a massless (dark radiation) and a massive (warm DM) species, with a lifetime Γ-1≃55(ϵ/0.007)1.4  Gyr—where ϵ represent the mass-energy fraction transferred to the massless component—can ease the tension. Thanks to a fast and accurate fluid approximation scheme for the warm species, we perform a comprehensive study of this two-body decaying DM scenario, discussing in detail its dynamics and its impact on the CMB and linear matter power spectra. We then investigate the implications for the S8 tension against a number of changes in the analysis: different S8 priors, marginalization over the lensing information in Planck data, trading Planck high-ℓ polarization data for those from the SPTpol and ACTPol surveys, and the inclusion of the recent results from the Xenon1T Collaboration. We conclude that the preference for decaying DM, apparent only when the S8 value determined from weak lensing data is added to the analysis, does not sensibly degrade the fit to any of the cosmological datasets considered, and that the model could potentially explain the anomalous electron recoil excess reported by the Xenon1T Collaboration. Furthermore, we explictly show that while current CMB data alone are not sensitive enough to distinguish between standard cold DM and decaying DM, next-generation CMB observations (CMB-S4) can unambiguously detect its signature

Ruling out QCD phase transition as a PBH origin of LIGO/Virgo events

The best-motivated scenario for a sizable primordial black hole (PBH) contribution to the LIGO/Virgo binary black hole mergers invokes the QCD phase transition, which naturally enhances the probability to form PBH with masses of stellar scale. We reconsider the expected mass function associated not only to the QCD phase transition proper, but also the following particle antiparticle annihilation processes, and analyse the constraints on this scenario from a number of observations: The specific pattern in cosmic microwave background (CMB) anisotropies induced by accretion onto PBHs, CMB spectral distortions, gravitational wave searches, and direct counts of supermassive black holes at high redshift. We find that the scenario is not viable, unless an ad hoc mass evolution for the PBH mass function and a cutoff in power-spectrum very close to the QCD scale are introduced by hand

Ruling out QCD phase transition as a PBH origin of LIGO/Virgo events

The best-motivated scenario for a sizable primordial black hole (PBH) contribution to the LIGO/Virgo binary black hole mergers invokes the QCD phase transition, which naturally enhances the probability to form PBH with masses of stellar scale. We reconsider the expected mass function associated not only to the QCD phase transition proper, but also the following particle antiparticle annihilation processes, and analyse the constraints on this scenario from a number of observations: The specific pattern in cosmic microwave background (CMB) anisotropies induced by accretion onto PBHs, CMB spectral distortions, gravitational wave searches, and direct counts of supermassive black holes at high redshift. We find that the scenario is not viable, unless an ad hoc mass evolution for the PBH mass function and a cutoff in power-spectrum very close to the QCD scale are introduced by hand