The History And Prehistory Of Human Disease

A new paper in Nature concludes from ancient DNA that while infectious diseases were common in humans since the hunter-gatherer era, that there was a real surge, not at the time of the Neolithic Revolution, but when steppe herders started to invade and conquerer farmers, and hunter-gatherers, possibly because they lived more closely with their animals and because the diseases that they carried helped facilitate their conquests. The New York Times also discusses the paper.

Infectious diseases have had devastating effects on human populations throughout history, but important questions about their origins and past dynamics remain. To create an archaeogenetic-based spatiotemporal map of human pathogens, we screened shotgun-sequencing data from 1,313 ancient humans covering 37,000 years of Eurasian history. We demonstrate the widespread presence of ancient bacterial, viral and parasite DNA, identifying 5,486 individual hits against 492 species from 136 genera. Among those hits, 3,384 involve known human pathogens, many of which had not previously been identified in ancient human remains. Grouping the ancient microbial species according to their likely reservoir and type of transmission, we find that most groups are identified throughout the entire sampling period. Zoonotic pathogens are only detected from around 6,500 years ago, peaking roughly 5,000 years ago, coinciding with the widespread domestication of livestock. Our findings provide direct evidence that this lifestyle change resulted in an increased infectious disease burden. They also indicate that the spread of these pathogens increased substantially during subsequent millennia, coinciding with the pastoralist migrations from the Eurasian Steppe

Martin Sikora, et al., "The spatiotemporal distribution of human pathogens in ancient Eurasia" Nature (July 9, 2025).

All the GUTs Worth Considering

A fairly short new paper (five pages plus seven pages of footnotes and an appendix) tries to list most or all of the possible Grand Unified Theories a.k.a. GUTs (i.e. theories the unify the three Lie groups of the Standard Model, but not gravity, into a single unified mathematical structure; unified theories that also include gravity are called Theories of Everything a.k.a. TOEs) that could include the Standard Model of Particle Physics, or an extension of it. 

There aren't all that many possibilities that are promising, and several decades of attempts to fit the Standard Model into one in a way that provides useful theoretical insight has not been very fruitful. While this line of inquiry isn't as troubled as supersymmetry (which is a dead man walking) or string theory (which is almost as troubled), it isn't very "hot" either.

Many potential GUTs, including the most minimal SU(5) GUT, would (1) imply violations of baryon number and/or lepton number conservation that aren't observed (e.g. proton decay, flavor changing neutral currents, and neutrinoless double beta decay), (2) lack some fundamental particles that are observed in the Standard Model, or (3) imply the existence of new fundamental particles beyond the Standard Model that haven't been observed (and in some cases, these particles have been ruled out to quite high energies). 

As a general rule, the bigger the Lie group of the unifying GUT, the more likely it is that it will imply far more new fundamental particles than there is any good reason to think that even a many particle dark sector should contain. Theoretical physicists prefer GUTs that imply as minimal an extension of the Standard Model as possible. Moreover, GUTs with certain kinds of new fundamental particles, such as those that imply more than three generations of fundamental Standard Model fermions, are strongly disfavored.

The experimental constraints on baryon number violating and lepton number violating processes (outside sphaleron interactions which are predicted in the Standard Model at extremely high energies but have not been observed) like proton decay, flavor changing neutral currents, and neutrinoless double beta decay are both very strict and very robust (i.e. they have been tested in multiple, independent ways). The exclusions of new fundamental particles are generally up to masses of several hundred to many thousands of GeVs, which is less strict, and the possibility of beyond the Standard Model fundamental particles is also strongly motivated (although not compelled) by the existence of dark matter phenomena. 

In the early days of GUT theories, a much sought after GUT property was that the three Standard Model forces unify at high enough energies in a manner that echos electroweak unification theory (which was one of the very attractive features of supersymmetry theory). But this has also been elusive. 

The Standard Model beta functions of the three Standard Model forces (electromagnetism, the weak force, and the strong force), which govern how the strength of these forces change with energy scale, extrapolated to arbitrarily high energy scales, based upon data all of the way up to the energy scales that can be reached by the Large Hadron Collider a.k.a. LHC (the highest energy scale high energy physics experiment every conducted), never unify. So, if a GUT the unifies the three Standard Model forces exists is some high energy scale, this must be due to new physics at energy scales above those that can be experimentally probed so far that is outside the domain of applicability of the Standard Model. 

Basically, given the energy scales that have already been reached by the LHC, energies at which the three Standard Model force could possibly unify haven't been present anywhere in the universe since some fraction of a second elapsed after the Big Bang. Of course, it is entirely possible that the three Standard Model forces simply don't unify at any energy scale that has ever existed or ever could exist.

Under a reasonable set of ab-initio assumptions, we define and chart the atlas of simple gauge theories with families of fermions whose masses are forbidden by gauge invariance. We propose a compass to navigate the atlas based on counting degrees of freedom. When searching for Grand-unification Theories with three matter generations, the free energy singles out the SU(5) Georgi-Glashow model as the minimal one, closely followed by SO(10) with spinorial matter. The atlas also defines the dryland of grand-unifiable gauge extensions of the standard model. We further provide examples relevant for gauge dual completions of the standard model as well as extensions by an additional SU(N) gauge symmetry.

Giacomo Cacciapaglia, Aldo Deandrea, Konstantinos Kollias, Francesco Sannino, "Grand-unification Theory Atlas: Standard Model and Beyond" arXiv:2507.06368 July 8, 2025).

The final paragraph of the conclusion of the main paper also enumerates some limitations on this paper serving as a truly comprehensive list of possibilities:

We have not considered yet scalar fields, as their mass cannot be prevented by any symmetry. Including spontaneous symmetry breaking of the gauge symmetry and generation of Yukawa couplings could imprint further constraints on the atlas, providing a phenomenological compass to navigate us towards the optimal high-energy theory. In our analysis, asymptotic freedom plays a crucial role in counting the degrees of freedom of each theory.

Non-Linear Cosmology Dynamics

Assuming the data has a Gaussian distribution (i.e. is distributed in a "normal" probability curve) is often reasonable, since this is what happens when data comes from independent simple percentage probability events. And, it is a convenient assumption when it works, because mathematically it is much easier to work with Gaussian distributions than most other probability distributions. But, sometimes reality is more complicated than that and this assumption isn't reasonable. 

The supernova data used to characterize dark energy phenomena isn't Gaussian. 

Trivially, this means that statistical uncertainty estimates based upon Gaussian distributions overestimate the statistical significance of observations in the fat tailed t-distribution. 

Non-trivially, this means that the underlying physics of dark matter phenomena are more mathematically complex than something like Newtonian gravity (often assumed for astronomy purposes as a reasonable approximation of general relativity) or a simple cosmological constant. Simple cosmology models don't match the data. 

This paper estimates dark energy parameters for more complex dark energy models that can fit the data.

Type Ia supernovae have provided fundamental observational data in the discovery of the late acceleration of the expansion of the Universe in cosmology. However, this analysis has relied on the assumption of a Gaussian distribution for the data, a hypothesis that can be challenged with the increasing volume and precision of available supernova data. 

In this work, we rigorously assess this Gaussianity hypothesis and analyze its impact on parameter estimation for dark energy cosmological models. We utilize the Pantheon+ dataset and perform a comprehensive statistical, analysis including the Lilliefors and Jarque-Bera tests, to assess the normality of both the data and model residuals. 

We find that the Gaussianity assumption is untenable and that the redshift distribution is more accurately described by a t-distribution, as indicated by the Kolmogorov Smirnov test. Parameters are estimated for a model incorporating a nonlinear cosmological interaction for the dark sector. The free parameters are estimated using multiple methods, and bootstrap confidence intervals are constructed for them.

Fabiola Arevalo, Luis Firinguetti, Marcos Peña, "On the Gaussian Assumption in the Estimation of Parameters for Dark Energy Models" arXiv:2507.05468 (July 7, 2025).