Search

Cosmic microwave background (CMB) experiments have deployed focal planes with O(104) transition edge sensor (TES) bolometers cooled to sub-Kelvin temperatures by multiplexing the readout of many TES channels onto a single pair of wires. Digital Frequency-domain Multiplexing (DfMux) is a multiplexing technique used in many CMB polarization experiments, such as the Simons Array, SPT-3 G, and EBEX. The DfMux system studied here uses LC filters with resonant frequencies ranging from 1.5 to 4.5 MHz connected to an array of TESs. Each detector has an amplitude-modulated carrier tone at the resonant frequency of its accompanying LC resonator. The signal is recovered via quadrature demodulation where the in-phase (I) component of the demodulated current is in phase with the complex admittance of the circuit and the quadrature (Q) component is orthogonal to I. Observed excess current noise in the Q component is consistent with fluctuations in the resonant frequency. This noise has been shown to be non-orthogonal to the phase of the detector's responsivity. We present a detailed analysis of the phase of responsivity of the TES and noise sources in our DfMux readout system. Further, we investigate how modifications to the TES operating resistance and bias frequency can affect the phase of noise relative to the phase of the detector responsivity, using data from Simons Array to evaluate our predictions. We find that both the phase of responsivity and phase of noise are functions of the two tuning parameters, which can be purposefully selected to maximize signal-to-noise (SNR) ratio.

There are many arguments against the possibility of experimenting on the whole universe. This system seems to be too big to be manipulated, it exists in only one exemplar and its evolution is a non-repeatable process. In this paper, I claim that we can nonetheless talk about experimentation in cosmology if we use Woodward's non-anthropocentric notion of intervention. However, Woodward and other interventionists argued that an intervention was necessarily an exogenous causal process and thus that no intervention on a closed system such as the universe was possible. I discuss their argument and I determine the conditions under which a consistent notion of endogenous intervention on the universe can be defined. Then, I show that there is at least one cosmic phenomenon satisfying these conditions: the photon decoupling. Finally, I draw some conclusions from this analysis regarding a realist approach of cosmology. [ABSTRACT FROM AUTHOR]

The common opinion that the Lorentz transformation distorts the Minkowski spacetime arises from a mathematically incorrect neglect of its non-diagonal terms. When the non-diagonal Lorentz transformation is properly treated, the time dilation and the space distortion disappear. Consequently, the Lorentz metric produced by the Lorentz transformation is identical to the Minkowski metric. The spacetime distortion in moving inertial frames is properly described by the so-called Doppler metric produced by the Doppler transformation. This transformation assumes the existence of a preferred frame and depicts the Doppler shift of light for a moving light source and/or observer. The Doppler metric is Lorentz invariant and leaves the Maxwell's equations unchanged from their form in the Minkowski spacetime. Moreover, the Doppler metric is experimentally confirmed because it yields the null result in the Michelson–Morley experiment and other interferometric experiments. The suitability of the Doppler metric for describing light properties in Special and General Relativity is supported by recent cosmological observations of the cosmic microwave background. [ABSTRACT FROM AUTHOR]

The 2020 decadal review recognized the measurement of the polarization of the cosmic microwave background (CMB) to be a top priority for the decade. CMB experiments including POLARBEAR2/Simons Array, Atacama Cosmology Telescope/Advanced-ACT, SPT-3G, the Simons Observatory, and CMB-S4 have or will use transition edge sensor (TES) bolometer fabricated with Aluminum doped with Manganese (AlMn). AlMn is a popular material choice as the superconducting transition temperature ( T c ) and normal resistance ( R n ) of the TES can be tuned with Mn concentration, geometric patterning, film thickness, and thermal annealing. In addition the conductivity is appropriate for both time division multiplexing and frequency division multiplexing that require 10 m Ω and 1 Ω sensors respectively. In this paper we present work on the ability to tune the T c of a film based on its time and temperature thermal tuning profile combined with room temperature monitoring of film resistivity. Such control allows for the fabrication of a wide range of TES parameters from a single AlMn concentration. Scanning electron microscope (SEM) imaging shows that the AlMn film's grain boundaries are changed by thermal annealing making the film more conductive and raising its superconducting transition temperatures, and that at high enough temperatures will eventually recover the T c of bulk Al. We find that baking films at ∼ 200 ∘ C for tens of minutes yields a T c that is suitable for 100 mK base temperature experiments and we present on the thermal tune profiles of several different thicknesses of AlMn. [ABSTRACT FROM AUTHOR]

Time-division multiplexing is the readout architecture of choice for many ground and space experiments, as it is a very mature technology with proven outstanding low-frequency noise stability, which represents a central challenge in multiplexing. Once fully populated, each of the two BICEP Array high-frequency receivers, observing at 150 GHz and 220/270 GHz, will have 7776 TES detectors tiled on the focal plane. The constraints set by these two receivers required a redesign of the warm readout electronics. The new version of the standard multichannel electronics, developed and built at the University of British Columbia, is presented here for the first time. BICEP Array operates time-division multiplexing readout technology to the limits of its capabilities in terms of multiplexing rate, noise and cross talk, and applies them in rigorously demanding scientific application requiring extreme noise performance and systematic error control. Future experiments like CMB-S4 plan to use TES bolometers with time-division/SQUID-based readout for an even larger number of detectors. [ABSTRACT FROM AUTHOR]

This research unveils a cutting-edge navigation system for deep space missions that utilizes cosmic microwave background (CMB) sensor readings to enhance spacecraft positioning and velocity estimation accuracy significantly. By exploiting the Doppler-shifted CMB spectrum and integrating it with optical measurements for celestial navigation, this approach employs advanced data processing through the Unscented Kalman Filter (UKF), enabling precise navigation amid the complexities of space travel. The simulation results confirm the system's exceptional precision and resilience in deep space missions, marking a significant advancement in astronautics and paving the way for future space exploration endeavors. [ABSTRACT FROM AUTHOR]

The cosmic microwave background (CMB) radiation, the relic afterglow of the Big Bang, has become one of the most useful and precise tools in modern precision cosmology. In this article, we employ Tsallis non-extensive statistical framework to calculate the cosmic microwave background (CMB) temperature and its probability distribution by utilising a recently proposed blackbody radiation inversion (BRI) technique and the cosmic background explorer/ far infrared absolute spectrophotometer (COBE/FIRAS) dataset. Here, we have used the best-fit values of q = 0.99888 ± 0.00016 and q = 1.00012 ± 0.00001, obtained by fitting COBE/FIRAS data with two different versions of non-extensive models. We compare the results with the more conventional extensive statistical analysis i.e. for q = 1. [ABSTRACT FROM AUTHOR]

In a recent paper [Phys. Rev. E 100, 023202 (2019)], Munirov and Fish proposed application of the well‐known approach for the calculation of the fluctuation field radiation spectrum in a transparent fully ionized plasma to the problem of cosmic microwave background. They used the result for spectral energy distribution of the equilibrium radiation, assuming that the spectrum of free photons is changed to the non‐damping spectrum of transverse waves in non‐relativistic plasma. The similar approach has been considered earlier by several authors for non‐relativistic and relativistic plasmas. The results of Munirov and Fish are in fact in perfect agreement with the most of the previously existing expressions. However, we argue that this approach based on such simple approximation is not enough justified and the more elaborated consideration, taking into account not only temporal but also spatial dispersion of dielectric permittivity is necessary for a consistent description of radiation in plasmas. Moreover, interaction between free photons and charged particles in the framework of quantum electrodynamics leads to the result different in comparison with the standard consideration even for the transparent plasma medium. [ABSTRACT FROM AUTHOR]

We present a novel methodology for exploring local features directly in the primordial power spectrum using a genetic algorithm pipeline coupled with a Boltzmann solver and Cosmic Microwave Background data (CMB). After testing the robustness of our pipeline using mock data, we apply it to the latest CMB data, including Planck 2018 and CamSpec PR4. Our model-independent approach provides an analytical reconstruction of the power spectra that best fits the data, with the unsupervised machine learning algorithm exploring a functional space built off simple 'grammar' functions. We find significant improvements upon the simple power-law behaviour, by Δχ2 ≲ −21, consistently with more traditional model-based approaches. These best-fits always address both the low-ℓ anomaly in the TT spectrum and the residual high-ℓ oscillations in the TT, TE, and EE spectra. The proposed pipeline provides an adaptable tool for exploring features in the primordial power spectrum in a model-independent way, providing valuable hints to theorists for constructing viable inflationary models that are consistent with the current and upcoming CMB surveys. [ABSTRACT FROM AUTHOR]

The question of the global topology of the Universe (cosmic topology) is still open. In the Λ CDM concordance model, it is assumed that the space of the Universe possesses the trivial topology of R 3 , and thus that the Universe has an infinite volume. As an alternative, in this paper, we study one of the simplest non-trivial topologies given by a cubic 3-torus describing a universe with a finite volume. To probe cosmic topology, we analyze certain structure properties in the cosmic microwave background (CMB) using Betti functionals and the Euler characteristic evaluated on excursions sets, which possess a simple geometrical interpretation. Since the CMB temperature fluctuations δ T are observed on the sphere S 2 surrounding the observer, there are only three Betti functionals β k (ν) , k = 0 , 1 , 2 . Here, ν = δ T / σ 0 denotes the temperature threshold normalized by the standard deviation σ 0 of δ T . The analytic approximations of the Gaussian expectations for the Betti functionals and an exact formula for the Euler characteristic are given. It is shown that the amplitudes of β 0 (ν) and β 1 (ν) decrease with an increasing volume V = L 3 of the cubic 3-torus universe. Since the computation of the β k 's from observational sky maps is hindered due to the presence of masks, we suggest a method that yields lower and upper bounds for them and apply it to four Planck 2018 sky maps. It is found that the β k 's of the Planck maps lie between those of the torus universes with side-lengths L = 2.0 and L = 3.0 in units of the Hubble length and above the infinite Λ CDM case. These results give a further hint that the Universe has a non-trivial topology. [ABSTRACT FROM AUTHOR]

The paper examines stochastic diffusion within an expanding space–time framework motivated by cosmological applications. Contrary to other results in the literature, for the considered general stochastic model, the expansion of space–time leads to a class of stochastic equations with non-constant coefficients that evolve with the expansion factor. The Cauchy problem with random initial conditions is posed and investigated. The exact solution to a stochastic diffusion equation on the expanding sphere is derived. Various probabilistic properties of the solution are studied, including its dependence structure, evolution of the angular power spectrum and local properties of the solution and its approximations by finite truncations. The paper also characterizes the extremal behaviour of the random solution by establishing upper bounds on the probabilities of large deviations. Numerical studies are carried out to illustrate the obtained theoretical results. [ABSTRACT FROM AUTHOR]

The transition-edge sensor (TES) as a type of low-temperature superconducting detector offers superior sensitivity due to its low thermal noise. In this work, we present a prototype TES bolometer designed for cosmic microwave background (CMB) polarization measurements. This TES is made of aluminum doped with a low concentration of manganese (2000 ppm by atomic percentage), and is deposited on the SiNx membrane which connects to the silicon substrate via narrow legs. In order to calculate its electrothermal parameters we have performed dark characterizations, which include measuring voltage-current (IV) curve at different bath temperatures, square-wave time response at various bias voltages, and noise level. This TES bolometer shows a noise equivalent power (NEP) of about 5 × 10 - 17 W/ Hz , which meets the requirement of CMB observation. However, its saturation power is smaller and time constant is larger than what are expected. We have analyzed the reasons and will make corresponding improvements in our future work. [ABSTRACT FROM AUTHOR]

Abstract During recombination, the cosmic background radiation is disturbed, in particular, by Lyman-alpha emissions from neutral hydrogen. It is proposed to account for the subsequent time-dependent partial thermalization of the Ly $$\alpha$$ α energy content in an analytically solvable nonlinear diffusion model. The amplitude of the partially thermalized and redshifted Ly $$\alpha$$ α line is found to be too low to be visible in the cosmic microwave spectrum, in accordance with previous numerical models and Planck observations.

We consider properties of dichroic antenna arrays on a silicon substrate with integrated cold-electron bolometers to detect radiation at frequencies of 210 and 240 GHz. This frequency range is widely used in cosmic microwave background experiments in space, balloon, and ground-based missions such as BICEP Array, LSPE, LiteBIRD, QUBIC, Simons Observatory, and AliCPT. As a direct radiation detector, we use cold-electron bolometers, which have high sensitivity and a wide operating frequency range, as well as immunity to spurious cosmic rays. Their other advantages are the compact size of the order of a few micrometers and the effect of direct electron cooling, which can improve sensitivity in typical closed-loop cycle 3He cryostats for space applications. We study a novel concept of cold-electron bolometers with two SIN tunnel junctions and one SN contact. The amplitude–frequency characteristics measured with YBCO Josephson Junction oscillators show narrow peaks at 205 GHz for the 210 GHz array and at 225 GHz for the 240 GHz array; the separation of these two frequency bands is clearly visible. The noise equivalent power level at an operating point in the current bias mode is 5 × 10−16 W/√Hz.

We report on the successful fabrication of orthomode transducer-coupled transition-edge sensor (TES) bolometer arrays for cosmic microwave background (CMB) polarimetry experiments with the superconductor electronics fabrication facility at SEEQC Inc. Commercial microfabrication foundry could provide increase in detector fabrication throughput for a next-generation CMB experiment, CMB-S4, that would deploy approximately one order of magnitude more detectors than current CMB experiments. We also developed TES bolometers with two TESs in series that have two different superconducting temperatures (Tc) using a superconducting proximity effect between niobium (Nb) and aluminum-manganese (AlMn) alloy. We will discuss the motivation, design considerations, fabrication processes, test results, and how industrial detector fabrication could be a path to fabricate hundreds of detector wafers for future CMB polarimetry experiments and other experiments that require TESs and superconducting RF circuits.

Lenslet-coupled antenna arrays have been used in CMB experiments and are the baseline technology for the next-generation satellite missions such as LiteBIRD and PICO. Lenslets are small hemispherical lenses mounted on the focal plane that couple light to the detectors and are typically made of silicon or alumina due to their high focusing power and low absorption loss. To minimize reflection at the vacuum-dielectric interface, lenslets require anti-reflection (AR) coatings. Metamaterials have been used in large microwave optical components because they avoid any mismatch on the thermal expansion between the lens and its coating, but so far they have only been machined on surfaces of comparatively large radius of curvature. As a first step to understand the feasibility of machining metamaterial AR layers in lenslets through laser-etching for the LiteBIRD mission, a model in ANSYS HFSS was developed. The goal of the simulation was to optimize transmission in three frequency bands while meeting assumed laser machinability constraints and optical requirements. Simulation results from flat silicon show that an AR metamaterial coating made under the assumed conditions is feasible, and the baseline parameters for further curved-surface studies are provided.

Digital Frequency-Domain Multiplexing (DfMux) is a technique that uses MHz superconducting resonators and Superconducting Quantum Interference Device (SQUID) arrays to read out sets of transition edge sensors. DfMux has been used by several Cosmic Microwave Background experiments, including most recently POLARBEAR-2 and SPT-3 G with multiplexing factors as high as 68, and is the baseline readout technology for the planned satellite mission LiteBIRD. Here, we present recent work focused on improving DfMux readout noise, reducing parasitic impedance, and improving sensor operation. We have achieved a substantial reduction in stray impedance by integrating the sensors, resonators, and SQUID array onto a single-carrier board operated at 250 mK. This also drastically simplifies the packaging of the cryogenic components and leads to better-controlled crosstalk. We demonstrate a low readout noise level of 8.6 pA / Hz 1 1 / 2, which was made possible by operating the SQUID array at a reduced temperature and with a low dynamic impedance. This is a factor of two improvement compared to the achieved readout noise level in currently operating Cosmic Microwave Background experiments using DfMux and represents a critical step toward maturation of the technology for the next generation of instruments.

This paper describes an experiment designed to observe potential changes in electromagnetic propagation velocity. It has been widely demonstrated that if the frequency of an electromagnetic wave is fixed, then the associated wavelength is causally related to c. Furthermore, the logical conclusion related to this known association (of frequency, wavelength, and light speed) is that, if the generated frequency during an experiment remains the same, and there is a velocity change in c, there would be causally related expansion or reduction in the associated wavelength. With the use of a Lecher line and a standing electromagnetic wave, the experimenter can measure changes in wavelength by measuring electrical output at an assigned position on a Lecher line. Results of this experiment demonstrated an obvious and experimentally repeatable phase change associated with rotation of the Lecher line. This phase change was demonstrated by a change in electrical output measured at the assigned location on the Lecher line. This experiment was repeated using various frequencies and voltage inputs into the Lecher line with obvious results that demonstrated an anisotropic difference. Further experiments were completed attempting to find an alternative hypothesis for the phase change noted in the original experiment, but these experiments were unable to identify an alternative cause of the phase change and consequently support the hypothesis that the phase change was directly related to anisotropy secondary to a change in the measured wavelength of the electromagnetic wave. Based upon the logical conclusions associated with this experiment and the results obtained, this experiment appears to demonstrate variable speed light. Furthermore, this discovery brings into question the theory that electromagnetic propagation though space is at the constant of c. [ABSTRACT FROM AUTHOR]

During recombination, the cosmic background radiation is disturbed, in particular, by Lyman-alpha emissions from neutral hydrogen. It is proposed to account for the subsequent time-dependent partial thermalization of the Ly α energy content in an analytically solvable nonlinear diffusion model. The amplitude of the partially thermalized and redshifted Ly α line is found to be too low to be visible in the cosmic microwave spectrum, in accordance with previous numerical models and Planck observations. [ABSTRACT FROM AUTHOR]

The focal plane of a telescope for cosmic microwave background (CMB) observation typically contains a large-scale array of transition-edge sensor (TES) bolometers. Polarized planar antennas are easy to fabricate and integrate, compared to commonly used horn antennas in receiving modules. In order to enhance the directivity and coupling efficiency, a planar antenna is generally equipped with a hyper-hemispherical silicon lens. However, a Si lens has a large volume, and the fabrication and assembly processes are complex. A flat all-dielectric metasurface lens is proposed to replace Si-lens to converge beam and increase gain of a slot antenna. The all-dielectric structure of silicon holes with sub-wavelength thickness can change the volumetric fill factor to adjust the local effective refractive index, and thus manipulate the shape of wavefront while ensuring high transmission efficiency. The meta-lens was found to exhibit high gain, low cross polarization and good beam symmetry, as verified by simulated electric field amplitude distribution and far-field patterns at 225 GHz using CST microwave studio suite. The detector array and the meta-lens array can both be fabricated using standard planar photolithography technology, and the combination has the potential to achieve larger scale arrays. [ABSTRACT FROM AUTHOR]

The Simons Observatory (SO) experiment is a cosmic microwave background (CMB) experiment located in the Atacama Desert, Chile. The SO's small aperture telescopes (SATs) consist of three telescopes designed for precise CMB polarimetry at large angular scales. Each SAT uses a cryogenic rotating half-wave plate (HWP) as a polarization modulator to mitigate atmospheric 1/f noise and other systematics. To realize efficient polarization modulation over the observation bands, we fabricated an achromatic HWP (AHWP) consisting of three sapphire plates with anti-reflection coatings. The AHWP is designed to have broadband modulation efficiency and transmittance. This paper reports on the design and the preliminary characterization of the AHWPs for SATs. [ABSTRACT FROM AUTHOR]

According to Einstein's cosmological principle, our universe at any fixed time is homogeneous and isotropic on large scales. It is thus modeled up to scaling by one of the following three three-dimensional maximally symmetric manifolds: the sphere, the Euclidean space, or the hyperbolic pseudosphere, none of which contain any privileged points or directions. We present several arguments which indicate why the last two unbounded manifolds cannot be good models of our physical universe at any fixed time. We shall then concentrate only on the expanding three-dimensional sphere. We prove that if its radius expands linearly, then the total travel time of a shuttle along geodesics around the entire universe is finite. If the shuttle has a constant velocity v > 0, its trajectory on such an expanding sphere is a logarithmic spiral. [ABSTRACT FROM AUTHOR]

The absence of large-angle correlations in the temperature of the cosmic microwave background (CMB), confirmed by three independent satellite missions, creates significant tension with the standard model of cosmology. Previous work has shown, however, that a truncation, kmin, of the primordial power spectrum comprehensively resolves the anomaly and the missing power at ℓ≲5 (the low multipoles). Since this cutoff is consistent with the hypothesized delay of inflation well beyond the Planck time, we are strongly motivated to consider its possible impact on other observational signatures. In this Letter, we analyze and predict its influence on the most revealing probe awaiting measurement by upcoming missions—the B-mode polarization of the CMB, whose accurate determination should greatly impact the inflationary picture. We highlight the quantitative power of this discriminant by specifically considering the LiteBIRD mission, predicting the effect of kmin on both the angular power spectrum and the angular correlation function of the B-mode, for a range of tensor-to-scalar ratios, r. While its impact on the latter appears to be negligible, kmin should have a very pronounced effect on the former. We show that for r=0.036, kmin's impact on CℓBB at low ℓ's should be easily detectable by LiteBIRD, but will be largely hidden by the total uncertainty of the measurement if r≲0.02.

Extending previous results, we explore aspects of the reheating mechanism for non-minimal Higgs inflation in the strong coupling regime. We constrain the radiative corrections for the inflaton's potential by considering the Coleman-Weinberg approximation and use the Renormalization Group Equations for the Higgs field to derive an upper limit on the top quark mass. Using the current Cosmic Microwave Background, Baryon Acoustic Oscillation, and Supernovae data, we obtain mt≤170.44 GeV, confirming the observational compatibility of the model with recent mt estimates reported by the CMS collaboration. We also analyze the breakdown of the well-known correlation involving the Hubble constant H0 and the clustering parameter σ8, which makes the model interesting in light of the cosmological tensions discussed over the last decade.

We point out that a modified temperature–redshift relation (T-z relation) of the cosmic microwave background (CMB) cannot be deduced by any observational method that appeals to an a priori thermalisation to the CMB temperature T of the excited states in a probe environment of independently determined redshift z. For example, this applies to quasar-light absorption by a damped Lyman-alpha system due to atomic as well as ionic fine-splitting transitions or molecular rotational bands. Similarly, the thermal Sunyaev-Zel’dovich (thSZ) effect cannot be used to extract the CMB’s T-z relation. This is because the relative line strengths between ground and excited states in the former and the CMB spectral distortion in the latter case both depend, apart from environment-specific normalisations, solely on the dimensionless spectral variable x=hνkBT. Since the literature on extractions of the CMB’s T-z relation always assumes (i) ν(z)=(1+z)ν(z=0), where ν(z=0) is the observed frequency in the heliocentric rest frame, the finding (ii) T(z)=(1+z)T(z=0) just confirms the expected blackbody nature of the interacting CMB at z>0. In contrast to the emission of isolated, directed radiation, whose frequency–redshift relation (ν-z relation) is subject to (i), a non-conventional ν-z relation ν(z)=f(z)ν(z=0) of pure, isotropic blackbody radiation, subject to adiabatically slow cosmic expansion, necessarily has to follow that of the T-z relation T(z)=f(z)T(z=0) and vice versa. In general, the function f(z) is determined by the energy conservation of the CMB fluid in a Friedmann–Lemaitre–Robertson–Walker universe. If the pure CMB is subject to an SU(2) rather than a U(1) gauge principle, then f(z)=1/41/3(1+z) for z≫1, and f(z) is non-linear for z∼1.

In this paper, we estimate the Cosmic Microwave Background (CMB) temperature using the data of the monopole spectrum from the Cosmic Background Explorer/ Far-Infrared Absolute Spectrophotometer (COBE/FIRAS). Utilising the idea of straight-line fitting, we obtain the temperature and chemical potential. The temperature of the CMB is found to be (2.725007 ± 0.000024) K (only statistical error) by using the monopole spectrum. Handling the data of the monopole spectrum the chemical potential is obtained as (-1.1 ± 3.4) × 10–5 with an upper bound |µ| < 5.7 × 10–5 (95% confidence level). The amplitude of the CMB dipole is found to be, Tamp = (3.47 ± 0.11) mK. We estimate an upper limit for the rms value of the fluctuation in chemical potential as Δµ < 1.2 × 10–4 (95% confidence level). The upper limit of y- distortion is calculated as y < 1.0 × 10–4 (95% confidence level). [ABSTRACT FROM AUTHOR]

The Background Imaging of Cosmic Extragalactic Polarization (BICEP)/Keck (BK) collaboration is currently leading the quest for the highest-sensitivity measurements of the polarized cosmic microwave background (CMB) anisotropies on a degree scale with a series of cryogenic telescopes, of which BICEP Array (BA) is the latest Stage-3 upgrade with a total of ∼ 32,000 detectors. The instrument comprises 4 receivers spanning 30–270 GHz, with the low-frequency 30/40 GHz deployed to the South Pole Station in late 2019. The full complement of receivers is forecast to set the most stringent constraints on the tensor-to-scalar ratio r. Building on these advances, the overarching small-aperture telescope concept is already being used as the reference for further Stage-4 experiment design. This paper describes the development of the BICEP Array 150 GHz detector module and its fabrication requirements, with highlights on the high-density time division multiplexing (TDM) design of the cryogenic circuit boards. The low-impedance wiring required between the detectors and the first stage of superconducting quantum interference device amplifiers is crucial to maintaining a stable bias current on the detectors. A novel multi-layer FR4 Printed Circuit Board with superconducting traces, capable of reading out up to 648 detectors, is detailed along with its validation tests. An ultra-high-density TDM detector module concept we developed for a CMB-S4-like experiment that allows up to 1920 detectors to be read out is also presented. TDM has been chosen as the detector readout technology for the Cosmic Microwave Background Stage-4 (CMB-S4) experiment based on its proven low-noise performance, predictable costs, and overall maturity of the architecture. The heritage for TDM is rooted in mm- and sub-mm-wave experiments dating back 20 years and has since evolved to support a multiplexing factor of 64x in Stage-3 experiments. [ABSTRACT FROM AUTHOR]

One of the main objectives of cosmology is the measurement of the Cosmic Microwave Background (CMB) polarization and, in particular, the so-called B-modes, which could demonstrate the existence of the primordial gravitational waves generated at the early stages of the Universe. For this reason, a new integrated version of the heterodyne polarimeter photonic part shown on a previously proposed scheme that can be used in both direct imaging and interferometric instruments is presented. We have tested its properties using specific commercial software, obtaining promising results. Working as a direct imaging instrument, it is shown that the proposed polarimeter can provide sufficiently low polarization angle and polarization efficiency systematic errors, which are considered acceptable for current ground-based CMB polarization experiments dedicated to the characterization of the foreground signals affecting the lowest part of the frequency spectrum. [ABSTRACT FROM AUTHOR]

We point out that a modified temperature–redshift relation (T-z relation) of the cosmic microwave background (CMB) cannot be deduced by any observational method that appeals to an a priori thermalisation to the CMB temperature T of the excited states in a probe environment of independently determined redshift z. For example, this applies to quasar-light absorption by a damped Lyman-alpha system due to atomic as well as ionic fine-splitting transitions or molecular rotational bands. Similarly, the thermal Sunyaev-Zel'dovich (thSZ) effect cannot be used to extract the CMB's T-z relation. This is because the relative line strengths between ground and excited states in the former and the CMB spectral distortion in the latter case both depend, apart from environment-specific normalisations, solely on the dimensionless spectral variable x = h ν k B T . Since the literature on extractions of the CMB's T-z relation always assumes (i) ν (z) = (1 + z) ν (z = 0) , where ν (z = 0) is the observed frequency in the heliocentric rest frame, the finding (ii) T (z) = (1 + z) T (z = 0) just confirms the expected blackbody nature of the interacting CMB at z > 0 . In contrast to the emission of isolated, directed radiation, whose frequency–redshift relation (ν -z relation) is subject to (i), a non-conventional ν -z relation ν (z) = f (z) ν (z = 0) of pure, isotropic blackbody radiation, subject to adiabatically slow cosmic expansion, necessarily has to follow that of the T-z relation T (z) = f (z) T (z = 0) and vice versa. In general, the function f (z) is determined by the energy conservation of the CMB fluid in a Friedmann–Lemaitre–Robertson–Walker universe. If the pure CMB is subject to an SU(2) rather than a U(1) gauge principle, then f (z) = 1 / 4 1 / 3 (1 + z) for z ≫ 1 , and f (z) is non-linear for z ∼ 1 . [ABSTRACT FROM AUTHOR]

In this paper, we report on the design, fabrication, and characterization of a 220 GHz superconducting transition edge sensor (TES) array developed for ground-based cosmic microwave background (CMB) experiments. Unlike conventional TES arrays adopting thermometers made of bilayer superconducting films, the TES array has thermometers made of simpler single-layer titanium (Ti) film deposited on a suspended silicon nitride (SiN x) membrane. The thermal weak link is realized by releasing the TES's thermal island including the Ti thermometer by dry etching with xenon difluoride (XeF2), giving a typical thermal conductance of 25 pW K−1. Its thermal-conductance mechanism is further studied by fitting the measured TES's complex impedance with a three-block thermal model. The dark and optical noise equivalent power (NEP) of a superconducting TES are both measured. Despite existing lens reflection and dielectric loss in the superconducting microstrip line, its typical optical NEP reaches 100 aW Hz−0.5, which meets the sensitivity requirement for ground-based CMB experiments. [ABSTRACT FROM AUTHOR]

This research unveils a cutting-edge navigation system for deep space missions that utilizes cosmic microwave background (CMB) sensor readings to enhance spacecraft positioning and velocity estimation accuracy significantly. By exploiting the Doppler-shifted CMB spectrum and integrating it with optical measurements for celestial navigation, this approach employs advanced data processing through the Unscented Kalman Filter (UKF), enabling precise navigation amid the complexities of space travel. The simulation results confirm the system’s exceptional precision and resilience in deep space missions, marking a significant advancement in astronautics and paving the way for future space exploration endeavors.

The question of the global topology of the Universe (cosmic topology) is still open. In the ΛCDM concordance model, it is assumed that the space of the Universe possesses the trivial topology of R3, and thus that the Universe has an infinite volume. As an alternative, in this paper, we study one of the simplest non-trivial topologies given by a cubic 3-torus describing a universe with a finite volume. To probe cosmic topology, we analyze certain structure properties in the cosmic microwave background (CMB) using Betti functionals and the Euler characteristic evaluated on excursions sets, which possess a simple geometrical interpretation. Since the CMB temperature fluctuations δT are observed on the sphere S2 surrounding the observer, there are only three Betti functionals βk(ν), k=0,1,2. Here, ν=δT/σ0 denotes the temperature threshold normalized by the standard deviation σ0 of δT. The analytic approximations of the Gaussian expectations for the Betti functionals and an exact formula for the Euler characteristic are given. It is shown that the amplitudes of β0(ν) and β1(ν) decrease with an increasing volume V=L3 of the cubic 3-torus universe. Since the computation of the βk’s from observational sky maps is hindered due to the presence of masks, we suggest a method that yields lower and upper bounds for them and apply it to four Planck 2018 sky maps. It is found that the βk’s of the Planck maps lie between those of the torus universes with side-lengths L=2.0 and L=3.0 in units of the Hubble length and above the infinite ΛCDM case. These results give a further hint that the Universe has a non-trivial topology.

Quantum cosmology aims to develop a quantum theory of the universe, attempting to answer open questions of physical cosmology, mainly related to the early epochs of the universe. Such a theory aims to unite relativity theory and quantum theory. Here, the whole universe is treated as a quantum mechanical system and is described by a wave function rather than by a classical spacetime. In this review, I shall describe the mathematical structure and primary formulations that form the backbone of quantum cosmology. We know that over a period of time, several approaches were developed to form a quantum theory of gravity. However, in order to decide which approach is the best, we need testable predictions, effects that can be observed in cosmic microwave background radiation (CMBR). I shall discuss the methodologies for generating quantum gravitational corrections to inflationary background leading to testable predictions. Another aspect of finding quantum imprints on CMBR results through the application of resolution of the 'quantum measurement problem' to early universe physics. In this article, I shall also discuss two such promising models explaining the classicalization of inflationary perturbation and are capable of leaving distinct observational imprints on the observables. [ABSTRACT FROM AUTHOR]

Over the past decade, the disparity between the value of the cosmic expansion rate determined directly from measurements of distance and redshift and that determined instead from the standard Lambda cold dark matter (ΛCDM) cosmological model, calibrated by measurements from the early Universe, has grown to a level of significance requiring a solution. Proposed systematic errors are not supported by the breadth of available data (and unknown errors are untestable by lack of definition). Simple theoretical explanations for this Hubble tension that are consistent with the majority of the data have been surprisingly hard to come by, but in recent years, attention has focused increasingly on models that alter the early or pre-recombination physics of ΛCDM as the most feasible. Here, we describe the nature of this tension and emphasize recent developments on the observational side. We then explain why early-Universe solutions are currently favored and the constraints that any such model must satisfy. We discuss one workable example, early dark energy, and describe how it can be tested with future measurements. Given an assortment of more extended recent reviews on specific aspects of the problem, the discussion is intended to be fairly general and understandable to a broad audience. [ABSTRACT FROM AUTHOR]

This paper presents a study of the performances of different Mach–Zehnder modulation technologies with applications in microwave polarimeters based on a near-infrared (NIR) frequency up-conversion stage, allowing for optical correlation and signal detection at a wavelength of 1550 nm. Commercial Mach–Zehnder modulators (MZMs) are traditionally implemented using LiNbO3 technology, which does not enable integration for the fabrication of MZMs. In this work, we propose the use of an alternative technology based on InP, which allows for integration in the fabrication process. In this way, it is possible to obtain advantages in terms of bandwidth, cost, and size reductions, which yield results that are very interesting for wide-band applications such as microwave instrumentation for the study of the cosmic microwave background (CMB). Here, we describe and compare the modulation performances of different MZMs, with one commercial unit presenting a higher bandwidth than those in previous works, and another three InP integrated units provided by the Fraunhofer Institute for Telecommunications, Heinrich-Hertz-Institute (HHI). Then, these modulators were coupled to a microwave polarimeter demonstrator, which has also been presented previously, to compare the polarization measurement performances of each of the MZMs. [ABSTRACT FROM AUTHOR]

About 70% of the Universe is Dark Energy, but the physics community still does not know what it is. Delta gravity (DG) is an alternative theory of gravitation that could solve this cosmological problem. Previously, we studied the Universe's accelerated expansion, where DG was able to explain the SNe-Ia data successfully. In this work, we computed the cosmological fluctuations in DG that give rise to the CMB through a hydrodynamic approximation. We calculated the gauge transformations for the metric and the perfect fluid to present the equations of the evolution of cosmological fluctuations. This provided the necessary equations to solve the scalar TT power spectrum in a semi-analytical way. These equations are useful for comparing the DG theory with astronomical observations and thus being able to constrain the DG cosmology. [ABSTRACT FROM AUTHOR]

AbstractThis Science White Paper, prepared in response to the ESA Voyage 2050 call for long-term mission planning, aims to describe the various science possibilities that can be realized with an L-class space observatory that is dedicated to the study of the interactions of cosmic microwave background (CMB) photons with the cosmic web. Our aim is specifically to use the CMB as a backlight – and survey the gas, total mass, and stellar content of the entire observable Universe by means of analyzing the spatial and spectral distortions imprinted on it. These distortions result from two major processes that impact on CMB photons: scattering by free electrons and atoms (Sunyaev-Zeldovich effect in diverse forms, Rayleigh scattering, resonant scattering) and deflection by gravitational potential (lensing effect). Even though the list of topics collected in this White Paper is not exhaustive, it helps to illustrate the exceptional diversity of major scientific questions that can be addressed by a space mission that will reach an angular resolution of 1.5 arcmin (goal 1 arcmin), have an average sensitivity better than 1 μK-arcmin, and span the microwave frequency range from roughly 50 GHz to 1 THz. The current paper also highlights the synergy of our Backlight mission concept with several upcoming and proposed ground-based CMB experiments.

The BICEP/Keck series of experiments target the cosmic microwave background at degree-scale resolution from the South Pole. Over the next few years, the "Stage-3" BICEP Array (BA) telescope will improve the program's frequency coverage and sensitivity to primordial B-mode polarization by an order of magnitude. The first receiver in the array, BA1, began observing at 30/40 GHz in early 2020. The next two receivers, BA2 and BA3, are currently being assembled and will map the southern sky at frequencies ranging from 95 to 150 GHz. Common to all BA receivers is a refractive, on-axis, cryogenic optical design that focuses microwave radiation onto a focal plane populated with antenna-coupled bolometers. High-performance antireflective coatings up to 760 mm in aperture are needed for each element in the optical chain, and must withstand repeated thermal cycles down to 4 K. Here, we present the design and fabrication of the 30/40 GHz anti-reflection coatings for the recently deployed BA1 receiver, with indices matched to its various polyethylene, nylon and alumina optical components. We describe an epoxy coating technique designed for alumina optics, which achieves better than 80% transmission at room temperature. For polyethylene optical elements, we present a new heat-compression approach that allows low-density polytetrafluoroethylene AR layers to reach sub-percent reflected power. We describe the planned use of these methods for the next BA cryostats, which may inform technological choices for future small-aperture telescopes of the CMB-S4 experiment. [ABSTRACT FROM AUTHOR]