No Arabic abstract
The heliocentric redshifts ($z_mathrm{hel}$) reported for 150 Type Ia supernovae in the Pantheon compilation are significantly discrepant from their corresponding values in the JLA compilation. Both catalogues include corrections to the redshifts and magnitudes of the supernovae to account for the motion of the heliocentric frame relative to the `CMB rest frame, as well as corrections for the directionally coherent bulk motion of local galaxies with respect to this frame. The latter is done employing modelling of peculiar velocities which assume the $Lambda$CDM cosmological model but nevertheless provide evidence for residual bulk flows which are discordant with this model (implying that the observed Universe is in fact anisotropic). Until recently such peculiar velocity corrections in the Pantheon catalogue were made at redshifts exceeding 0.2 although there is no data on which to base such corrections. We study the impact of these vexed issues on the 4.4 $sigma$ discrepancy between the Hubble constant of $H_0 = 67.4 pm 0.5$ km/s/Mpc inferred from observations of CMB anisotropies by Planck assuming $Lambda$CDM, and the measurement of $H_0 = 73.5 pm 1.4$ km/s/Mpc by the SH0ES project which extended the local distance ladder using Type Ia supernovae. Using the same methodology as the latter study we find that for supernovae whose redshifts are discrepant between Pantheon and JLA with $Delta z_mathrm{hel} > 0.0025$, the Pantheon redshifts favour $H_0 simeq 72$ km/s/Mpc, while the JLA redshifts favour $H_0 simeq 68$ km/s/Mpc. Thus the discrepancies between SNe Ia datasets are sufficient to undermine the claimed `Hubble tension. We further note the systematic variation of $H_0$ by $sim$ 6-9 km/s/Mpc across the sky seen in multiple datasets, implying that it cannot be measured locally to better than $sim$ 10% in a model-independent manner.
According to the Particle Data Group, the measurements of ${cal B}(W^+ to tau^+ u_tau)$ and ${cal B}(W^+ to ell^+ u_ell)$ ($ell = e,mu$) disagree with one another at the $2.3sigma$ level. In this paper, we search for a new-physics (NP) explanation of this $W to tau u$ puzzle. We consider two NP scenarios: (i) the $W$ mixes with a $W$ boson that couples preferentially to the third generation, (ii) $tau_{L,R}$ and $ u_{tau L}$ mix with isospin-triplet leptons. Unfortunately, once other experimental constraints are taken into account, neither scenario can explain the above experimental result. Our conclusion is that the $W to tau u$ puzzle is almost certainly just a statistical fluctuation.
The presence of a debris disc around the Gyr-old solar-type star $zeta^2,mathrm{Reticuli}$ was suggested by the $mathit{Spitzer}$ infrared excess detection. Follow-up observations with $mathit{Herschel}$/PACS revealed a double-lobed feature, that displayed asymmetries both in brightness and position. Therefore, the disc was thought to be edge-on and significantly eccentric. Here we present ALMA/ACA observations in Band 6 and 7 which unambiguously reveal that these lobes show no common proper motion with $zeta^2,mathrm{Reticuli}$. In these observations, no flux has been detected around $zeta^2,mathrm{Reticuli}$ that exceeds the $3sigma$ levels. We conclude that surface brightness upper limits of a debris disc around $zeta^2,mathrm{Reticuli}$ are $5.7,mathrm{mu Jy/arcsec^2}$ at 1.3 mm, and $26,mathrm{mu Jy/arcsec^2}$ at 870 microns. Our results overall demonstrate the capability of the ALMA/ACA to follow-up $mathit{Herschel}$ observations of debris discs and clarify the effects of background confusion.
The measurement of present-day temperature of the Cosmic Microwave Background (CMB), $T_0 = 2.72548 pm 0.00057$ K (1$sigma$), made by the Far-InfraRed Absolute Spectrophotometer (FIRAS), is one of the most precise measurements ever made in Cosmology. On the other hand, estimates of the Hubble Constant, $H_0$, obtained from measurements of the CMB temperature fluctuations assuming the standard $Lambda$CDM model exhibit a large ($4.1sigma$) tension when compared with low-redshift, model-independent observations. Recently, some authors argued that a slightly change in $T_0$ could alleviate or solve the $H_0$-tension problem. Here, we investigate evidence for a hotter or colder universe by performing an independent analysis from currently available temperature-redshift $T(z)$ measurements. Our analysis (parametric and non-parametric) shows a good agreement with the FIRAS measurement and a discrepancy of $gtrsim 1.9sigma$ from the $T_0$ values required to solve the $H_0$ tension. This result reinforces the idea that a solution of the $H_0$-tension problem in fact requires either a better understanding of the systematic errors on the $H_0$ measurements or new physics.
One of the problem revealed recently in cosmology is a so-called Hubble tension (HT), which is the difference between values of the present Hubble constant, measured by observation of the universe at redshift $z lesssim 1$, and by observations of a distant universe with CMB fluctuations originated at $z sim 1100$. In this paper we suggest, that this discrepancy may be explained by deviation of the cosmological expansion from a standard Lambda-CDM %simple Friedman model of a flat universe, during the period after recombination at $z lesssim 1100$, due to action of additional variable component of a dark energy of different origin.. We suppose, that a dark matter (DM) has a common origin with a variable component of a dark energy (DEV). DE presently may have two components, one of which is the Einstein constant $Lambda$, and another, smaller component DEV ($Lambda_V$) comes from the remnants of a scalar fields responsible for inflation. Due to common origin and interconnections the densities of DEV and DM are supposed to be connected, and remain almost constant during, at least, the time after recombination, when we may approximate $rho_{DM}=alpha rho_{DEV}$. This part of the dark energy in not connected with the cosmological constant $Lambda$, but is defined by existence of scalar fields with a variable density. Taking into account the influence of DEV on the universe expansion we find the value of $alpha$ which could remove the HT problem. In order to maintain the almost constant DEV/DM energy density ratio during the time interval at $z<1100$, we suggest an existence of a wide mass DM particle distribution.
Braneworld models with induced gravity exhibit phantom-like behaviour of the effective equation of state of dark energy. They can, therefore, naturally accommodate higher values of $H_0$, preferred by recent local measurements, while satisfying the CMB constraints. We test the background evolution in such phantom braneworld scenarios with the current observational datasets. We find that the phantom braneworld prefers a higher value of $H_0$ even without the R19 prior, thereby providing a much better fit to the local measurements. Although this braneworld model cannot fully satisfy all combinations of cosmological observables, among existing dark energy candidates the phantom brane provides one of the most compelling explanations of cosmic evolution.