Lucien Heurtier
@lucienheurtier.bsky.social
Theoretical Physicist at King's Coll. London @KCL_Physics #cosmology, #particles, #Universe, #darkmatter, #blackholes. Write fast, the Universe expands...
https://lheurtier.github.io/index.html
https://lheurtier.github.io/index.html
We applied this paradigm to the case of alpha-attractor E-models, which were recently disfavoured by CMB observations, in particular results from the Atacama Cosmology Telescope. What we fine is remarkable: accounting for this effect rescues alpha-attractors!
November 10, 2025 at 12:31 PM
We applied this paradigm to the case of alpha-attractor E-models, which were recently disfavoured by CMB observations, in particular results from the Atacama Cosmology Telescope. What we fine is remarkable: accounting for this effect rescues alpha-attractors!
Starting with initial de Sitter initial conditions, we find that the effect of the running increases with the growing curvature of the potential. In return, the negative curvature also grows, destabilising the slow-roll attractor much earlier than expected!
November 10, 2025 at 12:31 PM
Starting with initial de Sitter initial conditions, we find that the effect of the running increases with the growing curvature of the potential. In return, the negative curvature also grows, destabilising the slow-roll attractor much earlier than expected!
Taken together, the equations of motion for the potential flow, the metric and the inflaton field provide us a master system of equations (primes denote derivative wrt the number of e-folds) that we are to solve numerically:
November 10, 2025 at 12:31 PM
Taken together, the equations of motion for the potential flow, the metric and the inflaton field provide us a master system of equations (primes denote derivative wrt the number of e-folds) that we are to solve numerically:
Well, but if the Lagrangian is a function of H(t) and phi(t), the Friedmann equations also need to be upgraded. It gives this:
November 10, 2025 at 12:31 PM
Well, but if the Lagrangian is a function of H(t) and phi(t), the Friedmann equations also need to be upgraded. It gives this:
We then use a trick: rather than trying to evaluate the inverse of the D_E operator, we multiply both sides of this equation by D_E, providing us with an equation of motion for the potential flow, which looks like that:
November 10, 2025 at 12:31 PM
We then use a trick: rather than trying to evaluate the inverse of the D_E operator, we multiply both sides of this equation by D_E, providing us with an equation of motion for the potential flow, which looks like that:
Using the Local Potential Approximation (LPA), and a top hat regulator form, we obtain the following flow equation for the inflation potential U(phi,H):
November 10, 2025 at 12:31 PM
Using the Local Potential Approximation (LPA), and a top hat regulator form, we obtain the following flow equation for the inflation potential U(phi,H):
In a time-independent system, this cutoff scale can be varied from infinity (the purely classical limit) to zero (the full quantum theory), and the flow equation integrated over the flow, to recover one limit from the other.
November 10, 2025 at 12:31 PM
In a time-independent system, this cutoff scale can be varied from infinity (the purely classical limit) to zero (the full quantum theory), and the flow equation integrated over the flow, to recover one limit from the other.
In this set-up, the path integral leading to the calculation of the effective action is regulated to only incorporate quantum modes with frequencies larger than a cutoff scale k. Then, an exact flow equation of the effective action with respect to k is derived.
November 10, 2025 at 12:31 PM
In this set-up, the path integral leading to the calculation of the effective action is regulated to only incorporate quantum modes with frequencies larger than a cutoff scale k. Then, an exact flow equation of the effective action with respect to k is derived.
But wait, inflation potentials favoured by Planck/BICEP/Keck are all concave, no? Yes, that's fine, because not all quantum modes contribute to the path integral in that case. Only those that are sub-horizon. Super-horizon modes are IR/classical modes.
November 10, 2025 at 12:31 PM
But wait, inflation potentials favoured by Planck/BICEP/Keck are all concave, no? Yes, that's fine, because not all quantum modes contribute to the path integral in that case. Only those that are sub-horizon. Super-horizon modes are IR/classical modes.
In QFT, obtaining the effective potential for a classical background field requires performing a path integral over all quantum perturbations. Starting from an arbitrary potential, this typically leads to an effective potential that is convex.
November 10, 2025 at 12:31 PM
In QFT, obtaining the effective potential for a classical background field requires performing a path integral over all quantum perturbations. Starting from an arbitrary potential, this typically leads to an effective potential that is convex.
Such localised features included a gaussian dip or bump along the potential, or even monodromy potentials. The best fit we found (relatively to the power-law baseline V_alpha) are depicted here:
November 4, 2025 at 9:36 AM
Such localised features included a gaussian dip or bump along the potential, or even monodromy potentials. The best fit we found (relatively to the power-law baseline V_alpha) are depicted here:
We then asked the question: if that's what the data wants, what inflation potentials are able to produce such observables? The answer is: Not the vanilla ones. One needs some kind of local modulation of the potential that lead to variations of the power spectrum.
November 4, 2025 at 9:36 AM
We then asked the question: if that's what the data wants, what inflation potentials are able to produce such observables? The answer is: Not the vanilla ones. One needs some kind of local modulation of the potential that lead to variations of the power spectrum.
We found that adding the running and running of the running allows us to decrease this tension down to 2.8 sigmas. Results are presented here, where one can see that eBOSS demands for a negative running and running of the running.
November 4, 2025 at 9:36 AM
We found that adding the running and running of the running allows us to decrease this tension down to 2.8 sigmas. Results are presented here, where one can see that eBOSS demands for a negative running and running of the running.
We then allowed for the spectral index to run with energy scales, but also for its running to run as well! In other words, we allowed the amount of primordial perturbations to vary in a non-trivial manner over different scales.
November 4, 2025 at 9:36 AM
We then allowed for the spectral index to run with energy scales, but also for its running to run as well! In other words, we allowed the amount of primordial perturbations to vary in a non-trivial manner over different scales.
Unconverged MCMC corner plots are psychedelic. I think I will eventually open an art gallery. #cosmology #art #science
July 10, 2025 at 11:09 AM
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!
June 9, 2025 at 7:18 AM
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!
The winter edition of the conference will be hosted by Manchester University, stay tuned!
June 3, 2025 at 9:44 AM
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!
The winter edition of the conference will be hosted by Manchester University, stay tuned!
This plane company deeply cares about what their customers read.
No crappy magazines allowed 😄
No crappy magazines allowed 😄
April 1, 2025 at 2:57 PM
This plane company deeply cares about what their customers read.
No crappy magazines allowed 😄
No crappy magazines allowed 😄
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:
January 13, 2025 at 11:06 AM
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:
January 13, 2025 at 11:06 AM
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):
January 13, 2025 at 11:06 AM
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 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)
January 13, 2025 at 11:06 AM
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)
Big-Bang Nucleosynthesis (BBN) sets some of the most stringent constraints on PBHs, as their Hawking radiation may mess up with the formation of light nuclei (such as Deuterium, Helium 3, ...) in the early universe, whose abundance is measured with relatively good accuracy today (See plot below).
January 13, 2025 at 11:06 AM
Big-Bang Nucleosynthesis (BBN) sets some of the most stringent constraints on PBHs, as their Hawking radiation may mess up with the formation of light nuclei (such as Deuterium, Helium 3, ...) in the early universe, whose abundance is measured with relatively good accuracy today (See plot below).
Black Holes are unstable. They emit particles via Hawking radiation, and the lighter they are, the faster they evaporate, such that Primordial Black Holes (PBHs) lighter than about 1e15 grams would have evaporated by now.
January 13, 2025 at 11:06 AM
Black Holes are unstable. They emit particles via Hawking radiation, and the lighter they are, the faster they evaporate, such that Primordial Black Holes (PBHs) lighter than about 1e15 grams would have evaporated by now.