Another Challenge To ΛCDM That Dispenses With Cosmological Inflation

I have no idea why it took almost two weeks from submission for this preprint to be released by arXiv.

Recent discoveries, e.g., by JWST and DESI, have elevated the level of tension with inflationary ΛCDM. For example, the empirical evidence now suggests that the standard model violates at least one of the energy conditions from general relativity, which were designed to ensure that systems have positive energy, attractive gravity and non-superluminal energy flows.  

In this Letter, we use a recently compiled Type Ia supernova sample to examine whether ΛCDM violates the energy conditions in the local Universe, and carry out model selection with its principal competitor, the Rh=ct universe. We derive model-independent constraints on the distance modulus based on the energy conditions and compare these with the Hubble diagram predicted by both ΛCDM and Rh=ct, using the Pantheon+ Type Ia supernova catalog. 

We find that ΛCDM violates the strong energy condition over the redshift range z⊂(0,2), whereas Rh=ct satisfies all four energy constraints. At the same time, Rh=ct is favored by these data over ΛCDM with a likelihood of ∼89.5% versus ∼10.5%. The Rh=ct model without inflation is strongly favored by the Type Ia supernova data over the currrent standard model, while simultaneously adhering to the general relativistic energy conditions at both high and low redshifts.

Namit Chandak, Fulvio Melia, Junjie Wei, "Model selection with the Pantheon+ Type Ia SN sample" arXiv:2602.15047 (February 5, 2026) (4 pages, accepted for publication in A&A Letters).

Grab Bag Physics Articles

It may be possible to increase the precision with which the top quark mass is measured by a factor of ten to an uncertainty of plus or minus 30 MeV at a next generation positron-electron collider.

Constraints from Big Bang Nucleosynthesis significantly constrain the possibility of heavy neutral leptons (i.e. basically heavy, sterile neutrinos), allowing for the possible parameter space to be constrained from both above and below, potentially making it possible to rule out these hypothetical particles entirely, and in the meantime, focusing the search for them.

The Big Picture In Astrophysics Research

It is more statistical than an analytic description of the most important scientific advances, but it is still a notable overview. Certainly, there is no room to dispute that there has been a surge in astrophysics papers.

Over the past few years, Astrophysics has experienced an unprecedented increase in research output, as is evident from the year-over-year increase in the number of research papers put onto the arXiv. As a result, keeping up with progress happening outside our respective sub-fields can be exhausting. While it is impossible to be informed on every single aspect of every sub-field, this paper aims to be the next best thing. 

We present a summary of statistics for every paper uploaded onto the Astrophysics arXiv over the past year - 2025. We analyse a host of metadata ranging from simple metrics like the number of pages and the most used keywords, as well as deeper, more interesting statistics like the distribution of journals to which papers are submitted, the most used telescopes, the most studied astrophysical objects including GW, GRB, FRB events, exoplanets and much more. We also indexed the authors' affiliations to put into context the global distribution of research and collaboration. 

Combining this data with the citation information of each paper allows us to understand how influential different papers have been on the progress of the field this year. Overall, these statistics highlight the general current state of the field, the hot topics people are working on and the different research communities across the globe and how they function. 

We also delve into the costs involved in publications and what it means for the community. We hope that this is helpful for both students and professionals alike to adapt their current trajectories to better benefit the field.

Rommulus Francis Lewis, Hetansh Shah, Amruth Alfred, "Astrophysics Wrapped 2025: Year-in-Review of Every Astrophysics arXiv Paper from 2025" arXiv:2602.12303 (February 11, 2026).