Lucien Heurtier

Unconverged MCMC corner plots are psychedelic. I think I will eventually open an art gallery. #cosmology #art #science

After an intense week of organising two different conferences, now flying to Munich to relax and chat physics... and opening a little gem on the way!! Very comprehensive textbook! Strongly recommend it!

Yesterday, we hosted @kingsnmes.bsky.social King's College London the first edition of the UK-APP conference series, a new platform for discussion in astroparticle physics phenomenology funded by the IoP.

The winter edition of the conference will be hosted by Manchester University, stay tuned!

First day of the #Nehop 2025 conference in Brussels, a lot of fun to come!

After a few weeks off social media I open Bluesky hoping to read lots of new exciting research initiatives, but the most I read about is how visa fees in the UK and the Trump admin in the US are endangering past initiatives. Truly depressing.

One would hope a left wing government would stop letting immigrants pay more and more and dare to invest in publicly funded innovation, and yet...

This plane company deeply cares about what their customers read.

No crappy magazines allowed 😄

Or literally burn it themselves...

Can somebody explain to me what the heck is the usefulness of referencing a "private communication" in a paper?

Really sounds to me like "I used some secret scientific fact that some famous person told me about, so you've got to believe it, and sorry but you can't check it, it's private" 😕

Modest telescope with big plans, SPHEREx will probe cosmic ‘inflation’ after Big Bang Spacecraft with gather and analyze infrared light in new ways to explain why our universe is “boring”

Looking forward to this!

Thanks @danclery.bsky.social for the nice interview!

Modest telescope with big plans, SPHEREx will probe cosmic ‘inflation’ after Big Bang www.science.org/content/arti...
#cosmology #inflation #SPHEREx 🧪⚛️

‘My boss was crying.’ NSF confronts potentially massive layoffs and budget cuts Trump could propose slashing agency’s budget by two-thirds

The NSF budget reduced by two thirds. Incredible.

Public funding of research in the US will die if people don't react quickly.

www.science.org/content/arti...

The University of Pittsburgh pauses its Ph.D. admissions process amid research funding uncertainty A spokesperson for the University told WESA Friday that the school has "temporarily paused additional Ph.D. offers of admission," while Pitt works to understand how proposed federal funding cuts could...

It is starting. The US government idea of limiting to 15% indirect costs of research taken on research grants leads some universities to stop hiring PhD students.

This has to stop very quickly. It won't unless the American people protests or strikes as a whole.

www.wesa.fm/health-scien...

Based outside the UK and interested in a postdoc at King's College London in numerical GR/cosmology?

Contact Eugene @tukohbin.bsky.social!

How cosmic stasis may drastically rewrite the history of the universe

Unexpected epochs of stillness that punctuate the cosmic timeline could offer a natural explanation for dark matter and many other unsolved astronomical mysteries.

Nice! I hope you had great food in Pohang! Given what's written on the blackboard, what pedagogical reference would you recommend to learn about the Schwinger-Keldysh formalism?

In space, no-one can hear you scream – is it on pause?⏸️

In @newscientist.com, @lucienheurtier.bsky.social shares how the history of the cosmos could be defined by stillness, potentially turning the universe's history on it’s head🌌

https://buff.ly/4aVmg7o #Physics #Astronomy

These works were in collaboration with Keith Dienes, Fei Huang, Doojin Kim, Tim Tait, and Brooks Thomas!

In 2020, I discovered with my US collaborators a new paradigm for #cosmology and #particle #physics that we named "Cosmic Stasis".

We then published several works investigating the many implications of such a discovery.

This was featured this week in the New Scientist!

Article by Miriam Frankel.🧪

Note that for this edition UK-APP will be organised jointly with OWAN25, another event dedicated to the phenomenology of atmospheric neutrinos, so participants are invited to attend both events if they wish!

UK-APP and OWAN 25 conferences On June 2nd and 3rd 2025, King's College London will jointly host two conferences back to back: The semi-annual UK-APP conference and the OWAN 25 conference (see descriptions below). The two events ar...

UK-APP is born! 🧪

This new conference series dedicated to astroparticle physics phenomenology will take place for its first edition at King's Collefe London @kingsnmes.bsky.social on June 2nd 2025!

Put it on your calendar and register!

indico.global/event/13955/...

Who's this on the right 😉 @malcfairbairn.bsky.social

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Primordial Black Hole Hot Spots and Nucleosynthesis. Clelia Altomonte et. al. https://arxiv.org/abs/2501.05531

Primordial Black Hole Hot Spots and Nucleosynthesis Upon their evaporation via Hawking radiation, primordial black holes (PBHs) may deposit energy in the ambient plasma on scales smaller than the typical distance between two black holes, leading to the...

If you liked this thread, go and download our paper here: arxiv.org/abs/2501.05531. A big thanks again to my collaborators, @cleliaaltomonte.bsky.social and @malcfairbairn.bsky.social!

In conclusion: inhomogeneities matter! The hot spot size is smaller than the distance between PBHs. Temperature variations can thus severely affect the PBH capacity to radiate particles in the Universe. But also, we need to know more about the exact shape & dynamics of these hotspots! More to come!

See how limits may vary by almost an order of magnitude when accounting for the hot spot! We also noticed that the exact temperature profile of the hot spot affects the results a lot! See eg how the value of the benchmark coupling used in the hot spot derivation in (2210.06238) affects the results:

Once outside the hot spot, photons are quickly reprocessed to lower energy after scattering off electrons and photons in the plasma (purple curve in the plots above). Comparing results with and without hot spots provided us with a transfer function we could apply to existing BBN limits:

We evaluated the evolution of the photon mean-free path across the hot spot throughout the entire evaporation process, as well as the flux of photons that is radiated directly by the hot spot itself, and obtained the following results for PBHs with masses 1e11g, 1e12g, and 1e13g (left to right):

In our paper, we studied how the existence of such a hot spot may impact BBN constraints, focusing on the case of photodissociation, where low-energy photons produced by Hawking radiation dissociate light nuclei formed during BBN. Such constraints are relevant for PBHs with masses within 1e11-1e13g.

In fact, it is known that when Hawking radiation starts depositing energy into the plasma, it quickly creates a hot spot that surrounds PBHs and may screen a sizeable fraction of this radiation, forcing it to thermalising rather than free streaming (see eg arxiv.org/abs/2210.06238)

Well, there are arguments sustaining this hypothesis. After splitting into particles with lower and lower energies, Hawking radiation may indeed propagate on distances larger than the distance that separates PBHs. But that's assuming that this energy loss takes place in an homogeneous universe!