Cosmic Microwave Background Measurements Research Articles

Characterization of extragalactic point-sources on E- and B-mode maps of the CMB polarization

Although interesting in themselves, extragalactic sources emitting in the microwave range (mainly radio-loud active galactic nuclei and dusty galaxies) are also considered a contaminant from the point of view of Cosmic Microwave Background (CMB) experiments. These sources appear as unresolved point-like objects in CMB measurements because of the limited resolution of CMB experiments. Amongst other issues, point-like sources are known to obstruct the reconstruction of the lensing potential, and can hinder the detection of the Primordial Gravitational Wave Background for low values of r. Therefore, extragalactic point-source detection and subtraction is a fundamental part of the component separation process necessary to achieve some of the science goals set for the next generation of CMB experiments. As a previous step to their removal, in this work we present a new filter based on steerable wavelets that allows the characterization of the emission of these extragalactic sources. Instead of the usual approach of working in polarization maps of the Stokes' Q and U parameters, the proposed filter operates on E- and B-mode polarization maps. In this way, it benefits from the lower intensity that, both, the CMB, and the galactic foreground emission, present in B-modes to improve its performance. To demonstrate its potential, we have applied the filter to simulations of the future PICO satellite, and we predict that, for the regions of fainter galactic foreground emission in the 30 GHz and 155 GHz bands of PICO, our filter will be able to characterize sources down to a minimum polarization intensity of, respectively, 125 pK and 14 pK. Adopting a Π=0.02 polarization degree, these values correspond to 169 mJy and 288 mJy intensities.

The impact of new d(p,γ)3 rates on Big Bang Nucleosynthesis

We consider the effect on Big Bang Nucleosynthesis (BBN) of new measurements of the d(p,γ)3 cross section by the LUNA Collaboration. These have an important effect on the primordial abundance of D/H which is also sensitive to the baryon density at the time of BBN. We have re-evaluated the thermal rate for this reaction, using a world average of cross section data, which we describe with model-independent polynomials; our results are in good agreement with a similar analysis by LUNA.We then perform a full likelihood analysis combining BBN and Planck cosmic microwave background (CMB) likelihood chains using the new rate combined with previous measurements and compare with the results using previous rates. Concordance between BBN and CMB measurements of the anisotropy spectrum using the old rates was excellent. The predicted deuterium abundance at the Planck value of the baryon density was (D/H)BBN+CMB old = (2.57 ± 0.13) × 10−5 which can be compared with the value determined from quasar absorption systems (D/H)obs = (2.55 ± 0.03) × 10−5. Using the new rates we find (D/H)BBN+CMB = (2.51 ± 0.11) × 10−5.We thus find consistency among BBN theory, deuterium and 4 observations, and the CMB, when using reaction rates fit in our data-driven approach. We also find that the new reaction data tightens the constraints on the number of relativistic degrees of freedom during BBN, giving the effective number of light neutrino species Nν = 2.880 ± 0.144 in good agreement with the Standard Model of particle physics.Finally, we note that the observed deuterium abundance continues to be more precise than the BBN+CMB prediction, whose error budget is now dominated by d(d,n)3 and d(d,p)3 H. More broadly, it is clear that the details of the treatment of nuclear reactions and their uncertainty have become critical for BBN.

Hubble constant and sound horizon from the late-time Universe

We measure the expansion rate of the recent Universe and the calibration scale of the baryon acoustic oscillation (BAO) from low-redshift data. BAO relies on the calibration scale, i.e., the sound horizon at the end of drag epoch $r_d$, which often imposes a prior of the cosmic microwave background (CMB) measurement from the Planck satellite. In order to make really independent measurements of $H_0$, we leave $r_d$ completely free and use the BAO data sets combined with the 31 observational $H(z)$ data, GW170817 and Pantheon sample of Type Ia supernovae. In $\Lambda$CDM model, we get $H_0=68.63^{+1.75}_{-1.77}$ km s$^{-1}$ Mpc$^{-1}$, $r_d=146.85^{+3.29}_{-3.77}$ Mpc. For the two model-independent reconstructions of $H(z)$, we obtain $H_0=68.02\pm1.82$ km s$^{-1}$ Mpc$^{-1}$, $r_d=148.18^{+3.36}_{-3.78}$ Mpc in the cubic expansion, and $H_0=68.58\pm1.76$ km s$^{-1}$ Mpc$^{-1}$, $r_d=148.02^{+3.63}_{-3.60}$ Mpc in the polynomial expansion. The values of Hubble constant $H_0$ and sound horizon $r_d$ are consistent with the estimate derived from the Planck CMB data assuming a flat $\Lambda$CDM model, but $H_0$ is in $2.4\sim2.6$ $\sigma$ tension with SH0ES 2019, respectively.

A demonstration of improved constraints on primordial gravitational waves with delensing

We present a constraint on the tensor-to-scalar ratio, $r$, derived from measurements of cosmic microwave background (CMB) polarization $B$-modes with "delensing," whereby the uncertainty on $r$ contributed by the sample variance of the gravitational lensing $B$-modes is reduced by cross-correlating against a lensing $B$-mode template. This template is constructed by combining an estimate of the polarized CMB with a tracer of the projected large-scale structure. The large-scale-structure tracer used is a map of the cosmic infrared background derived from Planck satellite data, while the polarized CMB map comes from a combination of South Pole Telescope, BICEP/Keck, and Planck data. We expand the BICEP/Keck likelihood analysis framework to accept a lensing template and apply it to the BICEP/Keck data set collected through 2014 using the same parametric foreground modelling as in the previous analysis. From simulations, we find that the uncertainty on $r$ is reduced by $\sim10\%$, from $\sigma(r)$= 0.024 to 0.022, which can be compared with a $\sim26\%$ reduction obtained when using a perfect lensing template. Applying the technique to the real data, the constraint on $r$ is improved from $r_{0.05} < 0.090$ to $r_{0.05} < 0.082$ (95\% C.L.). This is the first demonstration of improvement in an $r$ constraint through delensing.

Multimessenger cosmology: Correlating cosmic microwave background and stochastic gravitational wave background measurements

Characterizing the physical properties of the stochastic gravitational waves background (SGWB) is a key step towards identifying the nature of its possible origin. We focus our analysis on SGWB anisotropies. The existence of a non-trivial primordial scalar-tensor-tensor (STT) correlation in the squeezed configuration may be inferred from the effect that a long wavelength scalar mode has on the gravitational wave power spectrum: an anisotropic contribution. Crucially, such contribution is correlated with temperature anisotropies in the cosmic microwave background (CMB). We show that, for inflationary models that generate suitably large STT non-Gaussianities, cross-correlating the CMB with the stochastic background of gravitational waves is a very effective probe of early universe physics. The resulting signal can be a smoking-gun for primordial SGWB anisotropies.

Primordial black holes as dark matter and gravitational waves from bumpy axion inflation

We consider a mechanism for producing a significant population of primordial black holes (PBHs) and an observable stochastic gravitational wave background (SGWB) within string theory inspired models of inflation. In this framework where inflaton is identified as a non-compact axion-like field, sub-leading non-perturbative effects can superimpose steep cliffs connected by smooth plateaus onto the underlying axion potential. In the presence of coupling to Abelian gauge fields, the motion of axion on the cliff-like region(s) of its potential triggers a localized production of one helicity state of gauge fields due to the temporary fast-roll of axion around such a feature. In this setup, primordial fluctuations sourced by vector fields exhibit a localized peak in momentum space corresponding to modes that exit the horizon when the axion velocity is maximal. As an application of this general mechanism, we present an example of axion inflation which both matches Planck observations at CMB scales and generates a population of light PBHs (MPBH ≃ 10−13 M⊙) that can account for all dark matter. In this scenario, the enhanced scalar fluctuations that leads to PBHs also generate an observable SGWB of induced origin at LISA scales. The amplitude and shape of the resulting GW signal inherits specific properties (such as non-Gaussianity and its shape) of its scalar sources that may allow us to distinguish this mechanism from other inflationary scenarios and astrophysical backgrounds. This GW signal together with an observation of PBH distribution at the corresponding scales can thus provide a window to the inflationary dynamics on scales much smaller than those probed by Cosmic Microwave Background (CMB) and Large Scale Structure (LSS) Measurements.

Dynamical dark energy after Planck CMB final release and H0 tension

ABSTRACT In this article we compare a variety of well-known dynamical dark energy models using the cosmic microwave background measurements from the 2018 Planck legacy and 2015 Planck data releases, the baryon acoustic oscillations measurements and the local measurements of H0 obtained by the SH0ES (Supernovae, H0, for the Equation of State of Dark energy) collaboration analysing the Hubble Space Telescope data. We discuss the alleviation of H0 tension, that is obtained at the price of a phantom-like dark energy equation of state. We perform a Bayesian evidence analysis to quantify the improvement of the fit, finding that all the dark energy models considered in this work are preferred against the ΛCDM scenario. Finally, among all the possibilities analysed, the CPL model is the best one in fitting the data and solving the H0 tension at the same time. However, unfortunately, this dynamical dark energy solution is not supported by the baryon acoustic oscillations (BAO) data, and the tension is restored when BAO data are included for all the models.

Reconciling Hubble constant discrepancy from holographic dark energy

Holographic dark energy (HDE) describes the vacuum energy in a cosmic IR region whose total energy saturates the limit of avoiding the collapse into a black hole. HDE predicts that the dark energy equation of the state transiting from greater than the $-1$ regime to less than $-1$, accelerating the Universe slower at the early stage and faster at the late stage. We propose the HDE as a new {\it physical} resolution to the Hubble constant discrepancy between the cosmic microwave background (CMB) and local measurements. With Planck CMB and galaxy baryon acoustic oscillation (BAO) data, we fit the HDE prediction of the Hubble constant as $H_0^{}\!=\, 71.54\pm1.78\,\mathrm{km\,s^{-1} Mpc^{-1}}$, consistent with local $H_0^{}$ measurements by LMC Cepheid Standards (R19) at $1.4\sigma$ level. Combining Planck+BAO+R19, we find the HDE parameter $c=0.51\pm0.02$ and $H_0^{}\! = 73.12\pm 1.14\,\mathrm{km \,s^{-1} Mpc^{-1}}$, which fits cosmological data at all redshifts. Future CMB and large-scale structure surveys will further test the holographic scenario.

Constraints on neutrino mass in the scenario of vacuum energy interacting with cold dark matter after Planck 2018

In this work, we investigate the constraints on the total neutrino mass in the scenario of vacuum energy interacting with cold dark matter (abbreviated as IΛCDM) by using the latest cosmological observations. We consider four typical interaction forms, i.e. , , , and , in the IΛCDM scenario. To avoid the large-scale instability problem in interacting dark energy models, we employ the extended parameterized post-Friedmann method for interacting dark energy to calculate the perturbation evolution of dark energy in these models. The observational data used in this work include the cosmic microwave background (CMB) measurements from the Planck 2018 data release, the baryon acoustic oscillation (BAO) data, the type Ia supernovae (SN) observation (Pantheon compilation), and the 2019 local distance ladder measurement of the Hubble constant H 0 from the Hubble Space Telescope. We find that, compared with those in the ΛCDM+ model, the constrains on are looser in the four IΛCDM+ models. When considering the three mass hierarchies of neutrinos, the constraints on are tightest in the degenerate hierarchy case and loosest in the inverted hierarchy case. In addition, in the four IΛCDM+ models, the values of coupling parameter β are larger using the CMB+BAO+SN+H 0 data combination than that using the CMB+BAO+SN data combination, and β > 0 is favored at more than 1σ level when using CMB+BAO+SN+H 0 data combination. The issue of the H 0 tension is also discussed in this paper. We find that, compared with the ΛCDM+ model, the H 0 tension can be alleviated in the IΛCDM+ model to some extent.

Probing dark matter with future CMB measurements

Dark Matter (DM) annihilation and decay during the Dark Ages can affect the cosmic ionization history and leave imprints in the Cosmic Microwave Background (CMB) anisotropy spectra. CMB polarization anisotropy can be sensitive to such energy injection at higher redshifts and help reducing degeneracy with primordial spectral parameters in $\Lambda$CDM and astrophysical ionization processes during reionization. In light of a number of upcoming CMB polarization experiments, such as AdvACTPol, AliCPT, CLASS, Simons Observatory, Simons Array, SPT-3G, we estimate their prospective sensitivity in probing dark matter annihilation and decay signals. We find that future missions have 95\% C.L. projected limits on DM decay and annihilation rates to orders of $\Gamma_\chi (\tau_{\chi}^{-1}) \sim 10^{-27}{\rm{s}}^{-1}$ and $\left<\sigma v \right>/m_{\chi} \sim 10^{-29}{\rm{cm^3s^{-1}GeV^{-1}}}$ respectively, significantly improving the sensitivity to DM from current experimental bounds.

Josephson Junctions and Cosmic Microwave Background

The implementation of utilizing superconducting quantum interference device (SQUID) readout for constant voltage biased transition edge sensors (TES) has enabled the detection of the infinitesimal fluctuation in cosmic microwave background (CMB). The properties of the fluctuations will provide us the information of the universe at the time that this light was first emitted. In short, by measuring the CMB today, we learn about the distant, ancient universe—how the universe began, what it is made of, and how it evolved to its current state. Over the past 20 years, we have achieved many successful CMB measurements with Josephson junctions. Brian, I offer my congratulations on your eight decades of life—Happy 80th birthday!

Post-inflationary axion isocurvature perturbations facing CMB and large-scale structure

Dark matter comprised of axion-like particles (ALPs) generated by the realignment mechanism in the post-inflationary scenario leads to primordial isocurvature fluctuations. The power spectrum of these fluctuations is flat for small wave numbers, extending to scales accessible with cosmological surveys. We use the latest measurements of Cosmic Microwave Background (CMB) primary anisotropies (temperature, polarization) together with CMB lensing, Baryonic Acoustic Oscillations (BAO) and Sunyaev Zel'dovich (SZ) cluster counts to measure the amplitude and tilt of the isocurvature component. We find preference for a white-noise isocurvature component in the CMB primary anisotropies; this conclusion is, however, weakened by current large-scale structure (LSS) data. Interpreting the result as a conservative upper limit on the isocurvature component, the combined bound on the ALP mass from all probes is ma ≳ 10−19 eV, with some dependence on how ma evolves with temperature. The expected sensitivity of cosmic shear and galaxy clustering from future LSS experiments and CMB lensing suggests improved bounds of ma ≳ 10−18–10−13 eV, depending on scale cuts used to avoid non-linearities and the ALP mass-temperature dependence.

Relieving the Hubble Tension with Primordial Magnetic Fields.

The standard cosmological model determined from the accurate cosmic microwave background measurements made by the Planck satellite implies a value of the Hubble constant H_{0} that is 4.2 standard deviations lower than the one determined from type Ia supernovae. The Planck best fit model also predicts higher values of the matter density fraction Ω_{m} and clustering amplitude S_{8} compared to those obtained from the Dark Energy Survey Year 1 data. Here we show that accounting for the enhanced recombination rate due to additional small-scale inhomogeneities in the baryon density may solve both the H_{0} and the S_{8}-Ω_{m} tensions. The additional baryon inhomogeneities can be induced by primordial magnetic fields present in the plasma prior to recombination. The required field strength to solve the Hubble tension is just what is needed to explain the existence of galactic, cluster, and extragalactic magnetic fields without relying on dynamo amplification. Our results show clear evidence for this effect and motivate further detailed studies of primordial magnetic fields, setting several well-defined targets for future observations.

Combining ILC and moment expansion techniques for extracting average-sky signals and CMB anisotropies

Abstract The method of weighted addition of multi-frequency maps, more commonly referred to as Internal Linear Combination (ILC), has been extensively employed in the measurement of cosmic microwave background (CMB) anisotropies and its secondaries along with similar application in 21cm data analysis. Here we argue and demonstrate that ILC methods can also be applied to data from absolutely-calibrated CMB experiments to extract average-sky signals in addition to the conventional CMB anisotropies. The performance of the simple ILC method is, however, limited, but can be significantly improved by adding constraints informed by physics and existing empirical information. In recent work, a moment description has been introduced as a technique of carrying out high precision modeling of foregrounds in the presence of inevitable averaging effects. We combine these two approaches to construct a heavily constrained form of the ILC, dubbed MILC, which can be used to recover tiny monopolar spectral distortion signals in the presence of realistic foregrounds and instrumental noise. This is a first demonstration for measurements of the monopolar and anisotropic spectral distortion signals using ILC and extended moment methods. We also show that CMB anisotropy measurements can be improved, reducing foreground biases and signal uncertainties when using the MILC. While here we focus on CMB spectral distortions, the scope extends to the 21cm monopole signal and B-mode analysis. We briefly discuss augmentations that need further study to reach the full potential of the method.

Impact of polarised extragalactic sources on the measurement of CMBB-mode anisotropies

One of the main goals of cosmology is to search for the imprint of primordial gravitational waves in the polarisation filed of the cosmic microwave background to probe inflation theories. One of the obstacles in detecting the primordial signal is that the cosmic microwave backgroundB-mode polarisation must be extracted from among astrophysical contaminations. Most efforts have focus on limiting Galactic foreground residuals, but extragalactic foregrounds cannot be ignored at the large scale (ℓ ≲ 150), where the primordialB-modes are the brightest. We present a complete analysis of extragalactic foreground contamination that is due to polarised emission of radio and dusty star-forming galaxies. We update or use current models that are validated using the most recent measurements of source number counts, shot noise, and cosmic infrared background power spectra. We predict the flux limit (confusion noise) for future cosmic microwave background (CMB) space-based or balloon-borne experiments (IDS, PIPER, SPIDER, LiteBIRD, and PICO), as well as ground-based experiments (C-BASS, NEXT-BASS, QUIJOTE, AdvACTPOL, BICEP3+Keck, BICEPArray, CLASS, Simons Observatory, SPT3G, and S4). The telescope aperture size (and frequency) is the main characteristic that affects the level of confusion noise. Using the flux limits and assuming mean polarisation fractions independent of flux and frequency for radio and dusty galaxies, we computed theB-mode power spectra of the three extragalactic foregrounds (radio source shot noise, dusty galaxy shot noise, and clustering). We discuss their relative levels and compare their amplitudes to that of the primordial tensor modes parametrised by the tensor-to-scalar ratior. At the reionisation bump (ℓ= 5), contamination by extragalactic foregrounds is negligible. While the contamination is much lower than the targeted sensitivity onrfor large-aperture telescopes at the recombination peak (ℓ= 80), it is at a comparable level for some of the medium- (∼1.5 m) and small-aperture telescope (≤0.6 m) experiments. For example, the contamination is at the level of the 68% confidence level uncertainty on the primordialrfor the LiteBIRD and PICO space-based experiments. These results were obtained in the absence of multi-frequency component separation (i.e. considering each frequency independently). We stress that extragalactic foreground contaminations have to be included in the input sky models of component separation methods dedicated to the recovery of the CMB primordialB-mode power spectrum. Finally, we also provide some useful unit conversion factors and give some predictions for the SPICA B-BOP experiment, which is dedicated to Galactic and extragalactic polarisation studies. We show that SPICA B-BOP will be limited at 200 and 350μm by confusion from extragalactic sources for long integrations in polarisation, but very short integrations in intensity.

Effects of Supernova Redshift Uncertainties on the Determination of Cosmological Parameters

Abstract Redshifts used in current cosmological supernova samples are measured using two primary techniques, one based on well-measured host galaxy spectral lines and the other based on supernova-dominated spectra. Here, we construct an updated Pantheon catalog with revised redshifts, redshift sources, and estimated uncertainties for the entire sample to investigate whether these two techniques yield consistent results. The best-fit cosmological parameters using these two measurement techniques disagree, with a supernova-only sample producing Ω m 3.2σ higher and H 0 2.5σ lower than a hostz-only sample, and we explore several possible sources of bias that could result from using the lower-precision supernova-dominated redshifts. In a pilot study, we show that using a host redshift-only subsample will generically produce lower Ω m and matter density Ω m h 2 and slightly higher H 0 than previous analysis which, for the Pantheon data set, could result in supernova and cosmic microwave background measurements agreeing on Ω m h 2 despite tension in H 0. To obtain rigorous results, though, the Pantheon catalog should be improved by obtaining host spectra for supernovae that have faded, and future surveys should be designed to use host galaxy redshifts rather than lower-precision methods.

H0 Reconstruction with Type Ia Supernovae, Baryon Acoustic Oscillation and Gravitational Lensing Time Delay

Abstract There is a persistent H 0-tension, now at more than ≳4σ level, between the local distance ladder value and the Planck cosmic microwave background measurement, in the context of flat Lambda-cold-dark-matter (ΛCDM) model. We reconstruct H(z) in a cosmological-model-independent way using three low-redshift distance probes including the latest data from baryon acoustic oscillation, supernova Ia (SN Ia) and gravitational lensing time-delay (GLTD) observations. We adopt general parametric models of H(z) and assume a Gaussian sound horizon at drag epoch, , from Planck measurement. The reconstructed Hubble constant H 0,rec using Pantheon SN Ia and Baryon Acoustic Oscillations (BAO) data are consistent with the Planck flat ΛCDM value. When including the GLTD data, H 0,rec increases mildly, yet remains discrepant with the local measurement at ∼2.2σ level. With our reconstructions being blind to the dark sectors at low redshift, we reaffirm the earlier claims that the Hubble tension is not likely to be solved by modifying the energy budget of the low-redshift universe. We further forecast the constraining ability of future realistic mock BAO data from Dark Energy Spectroscopic Instrument and GLTD data from Large Synoptic Survey Telescope, combining which, we anticipate that the uncertainty of H 0,rec would be improved by ∼27%, reaching uncertainty level.

Dark matter constraints on low mass and weakly coupled B−L gauge boson

We investigate constraints on the new $B-L$ gauge boson ($Z_{BL}$) mass and coupling ($g_{BL}$) in a $U(1)_{B-L}$ extension of the standard model (SM) with an SM singlet Dirac fermion ($\zeta$) as dark matter (DM). The DM particle $\zeta$ has an arbitrary $B-L$ charge $Q$ chosen to guarantee its stability. We focus on the small $Z_{BL}$ mass and small $g_{BL}$ regions of the model, and find new constraints for the cases where the DM relic abundance arises from thermal freeze-out as well as freeze-in mechanisms. In the thermal freeze-out case, the DM coupling is given by $g_{\zeta}\equiv g_{BL}Q\simeq0.016\sqrt{m_\zeta[{\rm GeV}]}$ to reproduce the observed DM relic density and $g_{BL}\geq 2.7 \times 10^{-8} \sqrt{m_\zeta[{\rm GeV}]}$ for the DM particle to be in thermal equilibrium prior to freeze-out. Combined with the direct and indirect DM detection constraints, we find that the allowed mass regions are limited to be $m_\zeta \gtrsim 200$ GeV and $M_{Z_{BL}} \gtrsim 10$ GeV. We then discuss the lower $g_{BL}$ values where the freeze-in scenario operates and find the following relic density constraints on parameters depending on the $g_{BL}$ range and dark matter mass: Case (A): for $g_{BL}\geq 2.7\times10^{-8}\sqrt{m_\zeta[{\rm GeV}]}$, one has $g^2_\zeta\,g^2_{BL}+\frac{0.82}{1.2}\,g^4_\zeta\simeq 8.2\times10^{-24}$ and Case (B): for $g_{BL} < 2.7 \times 10^{-8} \sqrt{m_\zeta[{\rm GeV}]}$, there are two separate constraints depending on $m_\zeta$. Case (B1): for $m_\zeta\lesssim 2.5{\rm TeV}$, we find $g_\zeta^2\,g_{BL}^2\simeq 8.2\times10^{-24}\,\left( \frac{m_\zeta}{2.5\,{\rm TeV}} \right)$ and case (B2): for $m_\zeta \gtrsim 2.5$ TeV, we have $g_\zeta^2 \, g_{BL}^2 \simeq 8.2 \times 10^{-24}$. For this case, we display the various parameter regions of the model that can be probed by a variety of ``Lifetime Frontier" experiments such as FASER, FASER2, Belle II, SHiP and LDMX.

Interacting dark energy in the early 2020s: A promising solution to the H0 and cosmic shear tensions

We examine interactions between dark matter and dark energy in light of the latest cosmological observations, focusing on a specific model with coupling proportional to the dark energy density. Our data includes Cosmic Microwave Background (CMB) measurements from the Planck 2018 legacy data release, late-time measurements of the expansion history from Baryon Acoustic Oscillations (BAO) and Supernovae Type Ia (SNeIa), galaxy clustering and cosmic shear measurements from the Dark Energy Survey Year 1 results, and the 2019 local distance ladder measurement of the Hubble constant $H_0$ from the Hubble Space Telescope. Considering Planck data both in combination with BAO or SNeIa data reduces the $H_0$ tension to a level which could possibly be compatible with a statistical fluctuation. The very same model also significantly reduces the $\Omega_{\rm m}-\sigma_8$ tension between CMB and cosmic shear measurements. Interactions between the dark sectors of our Universe remain therefore a promising joint solution to these persisting cosmological tensions.

A potentially detectable gamma-ray line in the Fermi Galactic center excess \u2014 in light of one-step cascade annihilations of secluded (vector) dark matter via the Higgs portal

We show the presence of a potentially detectable gamma-ray line in the Fermi Galactic center excess in light of the secluded (vector) dark matter (DM) model in which the hidden scalar, nearly degenerate with DM in mass, mediates the interaction of the secluded DM with the Standard Model (SM) due to its mixing with the SM Higgs. We find that the parameter region mX ∈ [60, 132] GeV can provide a good fit to the Fermi Galactic center gamma-ray excess spectrum, appearing a prominent gamma-ray line with the energy ∈ [30, 66] GeV. The best fit gives mX ≃ mS≃ 86 GeV with a p-value = 0.42, so that the resultant gamma-ray line, arising from the decay of the scalar mediator into γγ, peaks at 43 GeV. We derive constraints on the annihilation cross section from the Fermi- LAT gamma-ray line search, gamma-ray observations of the Fermi-LAT dwarf spheroidal galaxies, and Planck cosmic microwave background measurement. For the secluded vector DM model, the parameter space constrained by the current XENON1T and future LUX- ZEPLIN is shown. Finally, for the mixing angle between the Higgs sectors, we discuss its lower bound, which is required by the big bang nucleosynthesis constraint and relevant to the hidden sector decoupling temperature.