Hints of FLRW Breakdown from Supernovae

Abstract

A 10% difference in the scale for the Hubble parameter constitutes a clear problem for cosmology. As recently observed [1], only a modification to early Universe physics remains as a resolution within Einstein gravity plus the Friedmann-Lemaître-Robertson-Walker (FLRW) paradigm, but the current approaches are unconvincing, since they inflate other tensions. Here, working safely within FLRW and the flat ΛCDM cosmology, we observe that a correlation between higher H0 and the CMB dipole at high redshift, as observed in [1], can be extended from strongly lensed quasars to Pantheon Type Ia supernovae (SN) at > 2σ significance. Taken in tandem with mismatches between the CMB dipole and the dipole inferred from distant radio galaxies and quasars (QSOs), a resolution to Hubble tension outside of FLRW may be currently most compelling.

On Larger $H_0$ Values in the CMB Dipole Direction

“…From our end, FIG. 3 is reminiscent of similar features in strong lensing time delay [10] and Type Ia SN [34]. It remains to address caveats.…”

“…In particular, Hubble tension [1][2][3][4][5] casts a spotlight on H 0 = H(z = 0). Here, we build on earlier observations for strongly lensed QSOs [10] and Type Ia SN [34] that H 0 values in the direction of the CMB dipole, loosely defined, are larger. Similar variations of H 0 across the sky have been reported for scaling relations in galaxy clusters [35,36].…”

“…Concretely, we break the sky up into a 31 × 15 grid. Each point on this grid corresponds to two angles, which can be traded for a vector [34], v = [cos(DEC) cos(RA), cos(DEC) sin(RA), sin(DEC)]. (5) Observe that one gets the antipodal point on the sky by flipping the sign of DEC and shifting RA by 180 • , so by opting for an odd number of points in our grid, we include antipodal points.…”

A null test of the Cosmological Principle with BAO measurements

“…If we find strong inconsistencies between these measurements, they will hint at a violation of the CP -and thus require a profound reformulation of the standard model. In light of recent works that pointed out a potential FLRW breakdown [9][10][11][12][13][14][15], our goal is to verify the feasibility of these results using different data and methods. This paper is organised as follows: Section 2 is dedicated to describe the data and methodology herein deployed, section 3 presents the results, while section 4 contains the concluding remarks.…”

The Ellipsoidal Universe and the Hubble tension

“…In this respect, it is interesting to note that recent studies (see Refs. [17,18,19,20] and references therein) based on observations of quasars, supernovae and gamma ray bursts provided some evidences for an anisotropic departure from the Friedmann-Robertson-Walker metric. However, it is difficult to image physical processes able to generate sizeable anisotropies in early times.…”