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LiteBIRD is a candidate satellite for a strategic large mission of JAXA. With its expected launch in the middle of the 2020s with a H3 rocket, LiteBIRD plans to map the polarization of the cosmic microwave background radiation over the full sky with unprecedented precision. The full success of LiteBIRD is to achieve δ r < 0.001 , where δ r is the total error on the tensor-to-scalar ratio r . The required angular coverage corresponds to 2 ≤ ℓ ≤ 200 , where ℓ is the multipole moment. This allows us to test well-motivated cosmic inflation models. Full-sky surveys for 3 years at a Lagrangian point L2 will be carried out for 15 frequency bands between 34 and 448 GHz with two telescopes to achieve the total sensitivity of 2.5 μ K arcmin with a typical angular resolution of 0.5 ∘ at 150 GHz. Each telescope is equipped with a half-wave plate system for polarization signal modulation and a focal plane filled with polarization-sensitive TES bolometers. A cryogenic system provides a 100 mK base temperature for the focal planes and 2 K and 5 K stages for optical components.

We explore the possibility of detecting the excess of the cosmic radio background toward galaxy clusters due to its Compton scattering by electrons of the hot intergalactic gas. When mapping the background fluctuations at frequencies below MHz, this effect gives rise to a radio source at the location of the cluster. At higher frequencies, where the microwave (relic) radiation dominates in the cosmic background, a ‘‘negative’’ source (a ‘‘shadow’’ on the map of background fluctuations) is observed at the location of the cluster due to the transfer of some of the relic photons upward along the frequency axis upon their scattering (into the range GHz; Sunyaev and Zeldovich 1970, 1972). We have computed the spectra of the expected radio background distortions for various parameters of clusters and show that in many cases in the wide frequency range the measurement of the distortions will be hindered by the intrinsic thermal (bremsstrahlung) radiation from the intergalactic gas and the scattered radio emission from cluster galaxies associated with their past activity, including the synchrotron radiation from ejected relativistic electrons. Below MHz the scattering effect always dominates over the thermal gas radiation due to the general increase in the intensity of the cosmic radio background, but highly accurate measurements at such frequencies become difficult. Below MHz the effect is suppressed by the induced scattering. We have found the frequency ranges that are optimal for searching for and measuring the Compton radio background excess. We show that hot ( ) clusters at high ( ) redshifts are most promising for its observation. Because of the strong concentration of the bremsstrahlung to the cluster center, the peripheral observations of the Compton excess must be more preferable than the central ones. Moreover, owing to the thermal radiation of the gas and its concentration to the center, the above-noted transition from the ‘‘negative’’ source on the map of background fluctuations to the ‘‘positive’’ one when moving downward along the frequency axis must occur not gradually but through the stage of a ‘‘hybrid source’’—the appearance of a bright spot surrounded by a dark ring. This form of the source in projection is explained by its unusual three-dimensional shape in the form of a narrow radio bremsstrahlung peak rising from the center of a wide deep hole associated with the Compton scattering of the cosmic microwave background. The scattered radiation from an active central cluster galaxy in the past can amplify the effect. An analogous ‘‘hybrid source’’ also appears on the map of background fluctuations near a frequency of GHz—when passing from the deficit of the cosmic microwave background to its excess (due to the scattered photons). The unusual shape of the source is again associated with the thermal gas radiation. Simultaneous measurements of the radio bremsstrahlung flux from the gas and the amplitude of the distortions due to the radio and cosmic microwave background scattering will allow the most important cluster parameters to be determined.

Quantum fluctuations of the gravitational field in the early Universe, amplified by inflation, produce a primordial gravitational-wave background across a broad frequency band. We derive constraints on the spectrum of this gravitational radiation, and hence on theories of the early Universe, by combining experiments that cover 29 orders of magnitude in frequency. These include Planck observations of cosmic microwave background temperature and polarization power spectra and lensing, together with baryon acoustic oscillations and big bang nucleosynthesis measurements, as well as new pulsar timing array and ground-based interferometer limits. While individual experiments constrain the gravitational-wave energy density in specific frequency bands, the combination of experiments allows us to constrain cosmological parameters, including the inflationary spectral index nt and the tensor-to-scalar ratio r . Results from individual experiments include the most stringent nanohertz limit of the primordial background to date from the Parkes Pulsar Timing Array, ΩGW(f)<2.3×10−10 . Observations of the cosmic microwave background alone limit the gravitational-wave spectral index at 95% confidence to nt≲5 for a tensor-to-scalar ratio of r=0.11 . However, the combination of all the above experiments limits nt<0.36 . Future Advanced LIGO observations are expected to further constrain nt<0.34 by 2020. When cosmic microwave background experiments detect a nonzero r , our results will imply even more stringent constraints on nt and, hence, theories of the early Universe.

LiteBIRD is a next-generation satellite mission to measure the polarization of the cosmic microwave background (CMB) radiation. On large angular scales the B-mode polarization of the CMB carries the imprint of primordial gravitational waves, and its precise measurement would provide a powerful probe of the epoch of inflation. The goal of LiteBIRD is to achieve a measurement of the characterizing tensor to scalar ratio r to an uncertainty of δ r = 0.001 . In order to achieve this goal we will employ a kilo-pixel superconducting detector array on a cryogenically cooled sub-Kelvin focal plane with an optical system at a temperature of 4 K. We are currently considering two detector array options; transition edge sensor (TES) bolometers and microwave kinetic inductance detectors. In this paper we give an overview of LiteBIRD and describe a TES-based polarimeter designed to achieve the target sensitivity of 2  μ K arcmin over the frequency range 50–320 GHz.

Predicting the dynamics of many-body systems far from equilibrium is a challenging theoretical problem. A long-predicted phenomenon in hydrodynamic nonequilibrium systems is the occurrence of Sakharov oscillations, which manifest in the anisotropy of the cosmic microwave background and the large-scale correlations of galaxies. Here, we report the observation of Sakharov oscillations in the density fluctuations of a quenched atomic superfluid through a systematic study in both space and time domains and with tunable interaction strengths. Our work suggests a different approach to the study of nonequilibrium dynamics of quantum many-body systems and the exploration of their analogs in cosmology and astrophysics.

The standard model of cosmology is based on the existence of homogeneous surfaces as the background arena for structure formation. Homogeneity underpins both general relativistic and modified gravity models and is central to the way in which we interpret observations of the cosmic microwave background (CMB) and the galaxy distribution. However, homogeneity cannot be directly observed in the galaxy distribution or CMB, even with perfect observations, since we observe on the past light cone and not on spatial surfaces. We can directly observe and test for isotropy, but to link this to homogeneity we need to assume the Copernican principle (CP). First, we discuss the link between isotropic observations on the past light cone and isotropic space—time geometry: what observations do we need to be isotropic in order to deduce space—time isotropy? Second, we discuss what we can say with the Copernican assumption. The most powerful result is based on the CMB: the vanishing of the dipole, quadrupole and octupole of the CMB is sufficient to impose homogeneity. Real observations lead to near-isotropy on large scales—does this lead to near-homogeneity? There are important partial results, and we discuss why this remains a difficult open question. Thus, we are currently unable to prove homogeneity of the Universe on large scales, even with the CP. However, we can use observations of the cosmic microwave background, galaxies and clusters to test homogeneity itself.

We investigate how the dark energy properties impact the constraints on the total neutrino mass in interacting dark energy (IDE) models. In this study, we focus on two typical interacting dynamical dark energy models, i.e., the interacting w cold dark matter (I w CDM) model and the interacting holographic dark energy (IHDE) model. To avoid the large-scale instability problem in IDE models, we apply the parameterized post-Friedmann approach to calculate the perturbation of dark energy. We employ the Planck 2015 cosmic microwave background temperature and polarization data, combined with low-redshift measurements on baryon acoustic oscillation distance scales, type Ia supernovae, and the Hubble constant, to constrain the cosmological parameters. We find that the dark energy properties could influence the constraint limits on the total neutrino mass. Once dynamical dark energy is considered in the IDE models, the upper bounds of ∑ m v will be changed. By considering the values of χ 2 min , we find that in these IDE models the normal hierarchy case is slightly preferred over the inverted hierarchy case; for example, Δ χ 2 = 2.720 is given in the IHDE+∑ m v model. In addition, we also find that in the I w CDM+∑ m v model β = 0 is consistent with current observational data inside the 1 σ range, and in the IHDE+∑ m v model β > 0 is favored at more than 2 σ level.

The Cold Dark Matter (CDM) hypothesis accurately predicts large-scale structure formation and fits the Cosmic Microwave Background temperature fluctuations (CMB). However, observations of the inner regions of dark matter halos and dwarf galaxy satellites have consistently posed challenges to CDM. On the other hand, the Modified Newtonian Dynamics (MOND) hypothesis can explain galactic phenomena but fails to account for the complex shape of the CMB and matter power spectra. CDM and MOND are effective in nearly mutually exclusive regimes, prompting the question: is there a physical mechanism where CDM and MOND share a common origin? Q-balls, which are localized, non-topological solitons, can be a bridge between the two hypotheses. Q-balls formed in the early Universe can mimic CDM at cosmological scales. Interestingly, Q-balls can exhibit MOND-like behavior in the late Universe at galactic scales, providing a unified framework. Specifically, we demonstrate that millicharged composite Q-balls formed from complex scalar fields, decoupled from the background radiation, can naturally arise during the radiation-dominated epoch. From the matter-radiation equality, we also obtain the mass of Q-balls to be 1 eV, which are much smaller than the electron mass. Using the constraints from the invisible decay mode of ortho-positronium, we obtain Q < 3.4 × 10 - 5 . We also establish an upper bound on the number density of Q-balls, which depends on the charge of the Q-ball and the small initial charge asymmetry. Furthermore, we demonstrate that the MOND naturally emerges at the galactic scale within the framework of our Q-ball model.

We explore the possibility that both the suppression of the \\[\\ell = 2\\] multipole moment of the power spectrum of cosmic microwave background temperature fluctuations and the possible dip for \\[\\ell = 10\\]–30 can be explained as well as a possible new dip for \\[\\ell \\approx 60\\] as the result of the resonant creation of sequential excitations of a fermionic (or bosonic) closed superstring that couples to the inflaton field. We consider a D\\[\\,=\\,\\]26 closed bosonic string with one toroidal compact dimension as an illustration of how string excitations might imprint themselves on the CMB. We analyze the existence of successive momentum states, winding states or oscillations on the string as the source of the three possible dips in the power spectrum. Although the evidence of these dips are of marginal statistical significance, this might constitute the first observational evidence of successive superstring excitations in Nature.

The Fermi Gamma-ray Space Telescope has detected the γ-ray glow emanating from the giant radio lobes of the radio galaxy Centaurus A. The resolved γ-ray image shows the lobes clearly separated from the central active source. In contrast to all other active galaxies detected so far in high-energy γ-rays, the lobe flux constitutes a considerable portion (greater than one-half) of the total source emission. The γ-ray emission from the lobes is interpreted as inverse Compton-scattered relic radiation from the cosmic microwave background, with additional contribution at higher energies from the infrared-to-optical extragalactic background light.These measurements provide ã-ray constraints on the magnetic field and particle energy content in radio galaxy lobes, as well as a promising method to probe the cosmic relic photon fields.