Inflection-point Inflation and Dark Matter Redux

The cosmic microwave background (CMB) radiation, the relic of the early phases of the expanding universe, is bright, full of information, and difficult to measure. Along with the recession of galaxies and the primordial nucleosynthesis, it is one of the strongest signs that the Hot Big Bang Model of the universe is correct. It is brightest around 2 mm wavelength, has a temperature of \(T_{\mathrm{cmb}} = 2.72548 \pm 0.00057\) K, and has a blackbody spectrum within 50 parts per million. Its spatial fluctuations (around 0.01% on 1\({}^{\circ }\) scales) are possibly the relics of quantum mechanical processes in the early universe, modified by processes up to the decoupling at a redshift of about 1,000 (when the primordial plasma became mostly transparent). In the cold dark matter (DM) model with cosmic acceleration (\(\Lambda \)CDM), the fluctuation statistics are consistent with the model of inflation and can be used to determine other parameters within a few percent, including the Hubble constant, the \(\Lambda \) constant, the densities of baryonic and dark matter, and the primordial fluctuation amplitude and power spectrum slope. In addition, the polarization of the fluctuations reveals the epoch of reionization at a redshift approximately twice that determined from the Gunn-Peterson trough due to optically thick Lyman \(\alpha\) absorption in QSO spectra. It is of historic importance, and a testament to the unity of theory and experiment, that we now have a standard model of cosmology that is consistent with all of the observations.Current observational challenges include (1) improvement of the spectrum distortion measurements, especially at long wavelengths, where the measured background is unexpectedly bright; (2) the search for the B-mode polarization (the divergence-free part of the polarization map), arising from propagating gravitational waves; and (3) the extension of fluctuation measurements to smaller angular scales. Much more precise spectrum observations near 2 mm are likely and would test some very interesting theories. Current theoretical challenges include explanation of the dark matter and dark energy; understanding, estimating, and removing the interference of foreground sources that limit the measurements of the CMB; detailed understanding of the influence of nonequilibrium processes on the decoupling and reionization phases; and searches for signs of the second order or exotic processes (e.g., isocurvature fluctuations, cosmic strings, non-Gaussian fluctuations). At this writing, we await the cosmological results of the Planck mission.

We investigate the hypothesis that Coulomb-type interactions between dark matter (DM) and baryons explain the anomalously low 21 cm brightness-temperature minimum at redshift $z\ensuremath{\sim}17$ that was recently measured by the EDGES experiment. In particular, we reassess the validity of the scenario where a small fraction of the total DM is millicharged, focusing on newly derived constraints from Planck 2015 cosmic microwave background (CMB) data. Crucially, the CMB power spectrum is sensitive to DM--baryon scattering if the fraction of interacting DM is larger than (or comparable to) the fractional uncertainty in the baryon energy density. Meanwhile, there is a mass-dependent lower limit on the fraction for which the required interaction to cool the baryons sufficiently is so strong that it drives the interacting-DM temperature to the baryon temperature prior to their decoupling from the CMB. If this occurs as early as recombination, the cooling saturates. We precisely determine the viable parameter space for millicharged DM, and find that only a fraction $({m}_{\ensuremath{\chi}}/\mathrm{MeV})0.0115%\ensuremath{\lesssim}f\ensuremath{\lesssim}0.4%$ of the entire DM content, and only for DM-particle masses between 0.5 MeV--35 MeV, can be charged at the level needed to marginally explain the anomaly, without violating limits from SLAC, CMB, big bang nucleosynthesis (BBN), or stellar and SN1987A cooling. In reality, though, we demonstrate that at least moderate fine tuning is required to both agree with the measured absorption profile and overcome various astrophysical sources of heating. Finally, we point out that a $\ensuremath{\sim}0.4%$ millicharged DM component which is tightly coupled to the baryons at recombination may resolve the current $2\ensuremath{\sigma}$ tension between the BBN and CMB determinations of the baryon energy density. Future CMB-S4 measurements will be able to probe this scenario directly.

The cosmic stories : beginning, evolution, and present days of the universe

Many experiments exploring weakly interacting massive particles (WIMPs) such as direct, indirect and collider searches have been carried out until now. However, a clear signal of a WIMP has not been found yet and it makes us to suspect that WIMPs are questionable as a dark matter candidate. Taking into account this situation, we propose two models in which dark matter relic density is produced by decay of a metastable particle. In the first model, the metastable particle is a feebly interacting massive particle, which is the so-called FIMP produced by freeze-in mechanism in the early universe. In the second model, the decaying particle is thermally produced the same as the usual WIMP. However decay of the particle into dark matter is led by a higher dimensional operator. As a phenomenologically interesting feature of nonthermal dark matter discussed in this paper, a strong sharp gamma-ray emission as an indirect detection signal occurs due to internal bremsstrahlung, although some parameter space has already been ruled out by this process. Moreover combining other experimental and theoretical constraints such as dark matter relic density, big bang nucleosynthesis, collider, gamma-rays and perturbativity of couplings, we discuss the two nonthermal DM models.

We perform a comprehensive analysis for the light scalar dark matter (DM) in the Inert two Higgs doublet model (i2HDM) with compressed mass spectra, small mass splittings among three ℤ2 odd particles — scalar S, pseudo-scalar A, and charged Higgs H±. In such a case, the co-annihilation processes play a significant role to reduce DM relic density. As long as a co-annihilation governs the total interaction rate in the early universe, a small annihilation rate is expected to reach a correct DM relic density and its coupling λS between DM pair and Higgs boson shall be tiny. Consequently, a negligible DM-nucleon elastic scattering cross section is predicted at the tree-level. In this work, we include the one-loop quantum corrections of the DM-nucleon elastic scattering cross section. We found that the quartic self-coupling λ2 between ℤ2 odd particles indeed contributes the one-loop quantum correction and behaves non-trivially for the co-annihilation scenario. Interestingly, the parameter space, which is allowed by the current constraints considered in this study, can predict the DM mass and annihilation cross section at the present compatible with the AMS-02 antiproton excess. The parameter space can be further probed at the future high luminosity LHC.

Today, astronomers use different methods to study the structure and evolution of the universe. However, they will all be affected by other factors such as light or electromagnetic radiation. It is impossible to accurately observe the structure of the universe in the distant past. To find objects that fit the criteria, the existence of dark matter was assumed. It only has a gravitational effect and will be less affected. The composition and characteristics of dark matter are important research foundations. In this paper, the Cosmic Microwave Background (CMB) and power spectrum are used to study the status of dark matter in the universe. The search found Weakly Interacting Massive Particles (WIMPs) to be a candidate in the dark matter component. The three types of dark matter are cold dark matter, warm dark matter, and hot dark matter. Comparing their respective characteristics, it is concluded that cold dark matter (CDM) is the condition for observing large-scale structures. The result is that dark matter constitutes the second largest component of the universe. WIMPs are more suitable candidates than Neutrinos. CDM is best suited for studying large-scale structures over time. Eventually, it will be discovered that dark matter has strong stability, which will help astronomers find the process of universe evolution. Dark matter is also an important player that is best used to study the structure and evolution of the universe.

We investigate a well known scenario of interaction in the dark sector where the vacuum energy is interacting with cold dark matter throughout the cosmic evolution in light of the cosmic microwave background (CMB) data from final Planck 2018 release. In addition to this minimal scenario, we generalize the model baseline by including the properties of neutrinos, such as the neutrino mass scale (Mν) and the effective number of neutrino species (Neff) as free parameters, in order to verify the possible effects that such parameters might generate on the coupling parameter, and vice versa. As already known, we again confirm that in light of the Planck 2018 data, such dark coupling can successfully solve the H0 tension (with and without the presence of neutrinos). Concerning the properties of neutrinos, we find that Mν may be wider than expected within the ΛCDM model and Neff is fully compatible with three neutrino species (similar to ΛCDM prevision). The parameters characterizing the properties of neutrinos do not correlate with the coupling parameter of the interaction model. When considering the joint analysis of CMB from Planck 2018 and an estimate of H0 from Hubble Space Telescope 2019 data, we find an evidence for a non-null value of the coupling parameter at more than 3σ confidence-level. We also discuss the possible effects on the interacting scenario due to the inclusion of baryon acoustic oscillations data with Planck 2018. Our main results updating the dark sectors' interaction and neutrino properties in the model baseline, represent a new perspective in this direction. Clearly, a possible new physics in light of some dark interaction between dark energy and dark matter can serve as an alternative to ΛCDM scenario to explain the observable Universe, mainly in light of the current tension on H0.

We investigate the phenomenological effects of the nonholomorphic (NH) higgsino mass term, μ′, within the minimal supersymmetric standard model (MSSM) extended by a non-abelian flavor symmetry, referred to as the sNHSSM. This flavor symmetry enables a substantial reduction in the number of free parameters inherent to the MSSM, streamlining them from a large set to just eight. Our study explores the interplay between cold dark matter (CDM) relic density (ΩCDMh2) and the anomalous magnetic moment of the muon, (g−2)μ. We study correlations among the theoretical parameters that emerge from this interplay and are further constrained by experimental data such as the Higgs boson mass, B-physics observables, and the charge and color breaking minima constraints. Moreover, our findings reveal that incorporating the NH higgsino mass term opens up new regions of parameter space that were previously inaccessible.

Dark matter production in the early Universe: Beyond the thermal WIMP paradigm

The presence of light thermally coupled dark matter affects early expansion history and production of light elements during the Big Bang Nucleosynthesis. Specifically, dark matter that annihilates into Standard Model particles can modify the effective number of light species in the universe N eff, as well as the abundance of light elements created buring BBN. These quantities in turn affect the cosmic microwave background (CMB) anisotropy. We present the first joint analysis of small-scale temperature and polarization CMB anisotropy from Atacama Cosmology Telescope (ACT) and South Pole Telescope (SPT), together with Planck data and the recent primordial abundance measurements of helium and deuterium to place comprehensive bounds on the mass of light thermal-relic dark matter. We consider a range of models, including dark matter that couples to photons and Standard-Model neutrinos. We discuss the sensitivity of the inferred mass bounds on measurements of N eff, primordial element abundances and the baryon density, and quantify the sensitivity of our results to a possible existence of additional relativistic species. We find that the combination of ACT, SPT, and Planck generally leads to the most stringent mass constraint for dark matter that couples to neutrinos, improving the lower limit by 40%–80%, with respect to previous Planck analyses. On the other hand, the addition of ACT and SPT leads to a slightly weaker bound on electromagnetically coupled particles, due to a shift in the preferred values of Y p and N eff driven by the ground based experiments. In most scenarios, the combination of CMB data has a higher constraining power than the primordial abundance measurements alone, with the best results achieved when all data are combined. Combining all CMB measurements with primordial abundance measurements, we rule out masses below ∼4 MeV at 95% confidence, for all models.We show that allowing for new relativistic species can weaken the mass bounds for dark matter that couples to photons by up to an order of magnitude or more.Finally, we discuss the reach of the next generation of the CMB experiments in terms of probing the mass of the thermal relic dark matter.

Thermal relic dark matter below ∼10 GeV is excluded by cosmic microwave background data if its annihilation to visible particles is unsuppressed near the epoch of recombination. Usual model-building measures to avoid this bound involve kinematically suppressing the annihilation rate in the low-velocity limit, thereby yielding dim prospects for indirect detection signatures at late times. In this work, we investigate a class of cosmologically viable sub-GeV thermal relics with late-time annihilation rates that are detectable with existing and proposed telescopes across a wide range of parameter space. We study a representative model of inelastic dark matter featuring a stable state χ1 and a slightly heavier excited state χ2 whose abundance is thermally depleted before recombination. Since the kinetic energy of dark matter in the Milky Way is much larger than it is during recombination, χ1χ1→χ2χ2 upscattering can efficiently regenerate a cosmologically long-lived Galactic population of χ2, whose subsequent coannihilations with χ1 give rise to observable gamma-rays in the ∼1 MeV−100 MeV energy range. We find that proposed MeV gamma-ray telescopes, such as e-ASTROGAM, AMEGO, and MAST, would be sensitive to much of the thermal relic parameter space in this class of models and thereby enable both discovery and model discrimination in the event of a signal at accelerator or direct detection experiments. Published by the American Physical Society 2024

The principle of the constant light speed was proposed by Einstein as a hypothesis in 1905. It is one of the cornerstones of the theory of special relativity. In the next 120 years, physicists have continuously discussed the reasons for the constant light speed, but their understanding of the causes of the constant light speed remains in Einstein’s initial hypothesis stage. From 2017 to 2022, Chinese scholar Song Guanyi, according to the analysis of the cosmic microwave background radiation data found by American radio astronomers Arnold Penzias and Robert Wilson in 1964, realized that the cosmic microwave background radiation is that the early strong radiation light quantum during the long distance traveling constantly loses energy (redshift), and evolves into a microwave (wavelength from 0.3 ~ 75cm). The observations prove that the light quantum is not previously understood as an independent, indivisible particle entity, and it should be composed of two parts: matter and energy. Based on the change of the structure of light quantum, this paper interprets the following concepts of physics related to light quantum a. The light quantum is composed of two parts: ground state matter (ground state photon) and energy (dynamic energy). When the ground state photon is excited by the dynamic energy, it turns into a light quantum. The light quantum is propagated in a continuous collision (elastic collision) manner between the light quantum and the ground state photon. The ground state photon is the medium particle of the light quantum propagation. A light quantum from any light source in the universe is new-born, and its propagation velocity (in a vacuum) has the same value C (whether it is emitted from a stationary or moving object). b. Interpretation of wave-particle duality. c. The existence state of ether (essentially the ground state photon) and its action. d. The difference between light wave and electromagnetic wave. e. The reason for the deviation when the starlight passes near the sun. f. The cause of the redshift of the galaxy spectral lines observed from the earth. g. The existence form and characteristics of dark matter (essentially ether). h. The existence morphology and characteristics of dark energy (essentially it is the energy carried by the light quantum and formed after the ground state photon (dark matter) is excited by the limited (one share by one share) dynamic energy).

The coannihilation mechanism is a well-motivated alternative to the simple thermal freeze-out mechanism, where the dark matter relic density can be obtained through the coannihilation with a partner particle of similar mass with dark matter. When the partner particle is neutral, the inelastic nature of dark matter can help it to escape the direct detection limits. In this work, we focus on the coannihilation scenario in which the annihilation cross section is dominated by the partner-partner pair annihilation. We pay special interest on the parameter space where the coannihilation partner is long-lived, which leads to displaced signatures at the collider. In such case, it opens the heavy mass parameter space for the coannihilation dark matter, comparing with those dominated by the partner-dark matter annihilation. Specifically, we study an inelastic scalar dark matter model with a specific parameter space, which realizes the domination of partner-partner pair annihilation. Then, we study two different realizations of the coannihilation partner decay and the existing constraints from the relic abundance, direct and indirect dark matter detection and the collider searches. We focus on the channel that the long-lived coannihilation partner decays to dark matter plus leptons. The high-luminosity LHC can reach good sensitivities for such heavy dark matter and coannihilation partner around 100–700 GeV.

A pressureless dark matter component fits well with several cosmological observations. However, there are indications that cold dark matter may encounter challenges in explaining observations at small scales, particularly at galactic scales. Observational data suggest that dark matter models incorporating a pressure component could provide solutions to these small-scale problems. In this work, we investigate the possibility that present-day dark matter may result from a decaying noncold dark matter sector transitioning into the dark energy sector. As the sensitivity of astronomical surveys rapidly increases, we explore an interacting scenario between dark energy and noncold dark matter, where dark energy has a constant equation of state (${w}_{\mathrm{de}}$), and dark matter, being noncold, also has a constant (non-zero) equation of state (${w}_{\mathrm{dm}}$). Considering the phantom and quintessence nature of dark energy, characterized by its equation of state, we separately analyze interacting phantom and interacting quintessence scenarios. We constrain these scenarios using cosmic microwave background (CMB) measurements and their combination with external probes, such as DESI-BAO and PantheonPlus. From our analyses, we find that a very mild preference for noncold dark matter cannot be excluded based on the employed datasets. Additionally, for some datasets, there is a pronounced preference for the presence of an interaction at more than 95% confidence level (CL). Moreover, when the dark energy equation of state lies in the phantom regime, the ${S}_{8}$ tension can be alleviated. This study suggests that cosmological models incorporating a noncold dark matter component should be considered as viable scenarios with novel phenomenological implications, as reflected in the present work.

micrOMEGAs5.0 : Freeze-in