Looping in the Primordial Universe

Contribution List

62. Opening

28/10/2024, 09:00

57. On loops in inflation

Leonardo Senatore

28/10/2024, 09:15

I will discuss several aspects of loop effects in single and multifield inflation.

56. Loops in the separate universe framework

David Seery

28/10/2024, 10:00

In this talk I will review the separate universe framework as a tool to perform loop calculations during and after inflation. I will describe recent work (with L. Iacconi and D. Mulryne) in which we use this framework to calculate loops representing a cascade of power from short scales to much longer, infrared scales. The backreaction associated with this cascade can destroy our ability to...

20. The Cosmological CPT Theorem (online)

Ayngaran Thavanesan (University of Cambridge)

28/10/2024, 11:30

In the original CPT theorem, one is restricted to flat space and is unable to make converse statements. In this talk, I will show how we can reformulate the CPT theorem using a symmetry argument to make converse statements and generalise it to beyond flat space. This in turn allows us to make a non-perturbative statement of unitarity in cosmology. I will show that this applies to the...

26. Simplicity of In-In correlators (online)

Chandramouli Chowdhury (University of Southampton)

28/10/2024, 11:50

We compute loop integrals of in-in correlators in dS for scalar theories and comment on the nature of the functions encountered and the simplicity observed compared to loops of wave functions (which can be equivalently thought of as AdS correlators).

This is based on upcoming work and 2312.13803, 2408.00074

23. Cosmological Correlators From Flat Space Feynman Integrals

Sadra Jazayeri (Imperial College London)

28/10/2024, 12:10

In this talk, I present a novel connection between cosmological correlators and flat-space Feynman diagrams in momentum space. Focusing on Witten diagrams with heavy internal lines and light external legs, I establish a Massive Flat Space (MFS) limit. In this limit, such heavy diagrams simplify to contact graphs with a vertex factor equal to the amputated n-point diagram in flat space. As...

58. Looping with combinatorics

Paolo Benincasa

28/10/2024, 14:00

Understanding the loop corrections to cosmological observables can have both phenomenological and theoretical implication: on the one hand, the coupling between the inflaton and fermions first appears at one-loop, and on the other hand they allow to have control on the quantum consistency of a theory in an expanding universe as well as to get a better handle on aspects of the framework...

52. Perturbative unitarity bounds from entanglement

Carlos Duaso Pueyo

28/10/2024, 14:45

When is it necessary to compute loop corrections in cosmology, or to introduce new physics in a theory? For which values of the parameters does perturbation theory break down? In particle physics, sharp bounds for the validity of the perturbative expansion are given by partial wave unitarity. Unfortunately these bounds don't extend to curved spacetime where scattering experiments are difficult...

30. Cosmological correlators in slow-roll violating inflation

Jason Kristiano

29/10/2024, 09:15

We present correlation functions of the curvature perturbation in single-field inflation model with violation of SR approximation up to second-order expansion of the in-in perturbation theory. We show that the soft limit of trispectrum is proportional to running of the bispectrum, which is a generalization of Maldacena's theorem. With the same cubic and quartic couplings that yields consistent...

53. The one-loop power spectrum of curvature fluctuations in ultra slow-roll inflation

Guillermo Ballesteros

29/10/2024, 10:00

I will discuss the ratio of the one-loop to the tree-level power spectrum of curvature fluctuations in a toy model of USR inflation, with the aim of discerning if perturbation theory breaks in related scenarios of PBH dark matter.

24. Cancellation of quantum corrections on the soft curvature perturbations

Yuichiro TADA (Nagoya University)

29/10/2024, 11:30

We study the cancellation of quantum corrections on the superhorizon curvature perturbations from subhorizon physics beyond the single-clock inflation from the viewpoint of the cosmological soft theorem. As an example, we focus on the transient ultra-slow-roll inflation scenario and compute the one-loop quantum corrections to the power spectrum of curvature perturbations taking into account...

25. Curvature Perturbations Protected Against One Loop

Keisuke Inomata (Jonhs Hopkins University)

29/10/2024, 11:50

We examine one-loop corrections from small-scale curvature perturbations to the superhorizon-limit ones in single-field inflation models, which have recently caused controversy. We consider the case where the Universe experiences transitions of slow-roll (SR) → intermediate period → SR. The intermediate period can be an ultra-slow-roll period or a resonant amplification period, either of which...

48. Absence of one-loop effects on large scales from small scales

Jacopo Fumagalli

29/10/2024, 12:10

I will discuss loop corrections to the large-scale primordial power spectrum induced by short-wavelength modes. In transient non-slow-roll dynamics, the relevance of these corrections has been recently the subject of intense debate. This underscores that in models with enhanced scalar fluctuations, many of the standard procedures employed in single-field slow-roll inflation may require...

49. Weyl Fermion Creation by Cosmic Perturbations at 1-loop

Azadeh Maleknejad

29/10/2024, 14:00

Weyl spin 1/2 fermions, when minimally coupled to Einstein's gravity, cannot be produced purely gravitationally in an expanding universe at tree level. However, this picture changes at the gravitational 1-loop level in the presence of cosmic perturbations, leading to a new and unavoidable mechanism for gravitational particle production. In this talk, I will explore the theory and...

27. Gravitational waves in ultra-slow-roll and their anisotropy at two loops

Julian Leonardo Rey Idler

29/10/2024, 14:45

We use the in-in formalism to compute the non-Gaussian corrections to the energy density and anisotropies of gravitational waves induced after an ultra-slow-roll phase of inflation by using a diagrammatic approach and present the corresponding Feynman rules. Our two-loop calculation includes both the intrinsic non-Gaussianity of the inflaton perturbation $\delta\phi$ and the non-Gaussianity...

55. Finite parts of inflationary loops

Flavio Riccardi

29/10/2024, 15:05

The objective of this talk is to present a systematic approach for calculating loop corrections, including finite contributions, to the power spectrum in a cosmological setting. Particular emphasis will be placed on the renormalization procedure, comparing the results obtained using different regularization methods.

34. Thematic discussion 1

29/10/2024, 16:15

46. Renormalizing UV Divergences in the Early Universe -- What can go wrong?

Anna Negro

30/10/2024, 09:15

In this talk, we examine some of the challenges that can arise when renormalizing UV divergences in cosmological settings. One fundamental step of renormalization is regularization. Hence, we start by introducing two of the most commonly used regularization schemes: hard cutoffs and dimensional regularization. Specifically, we demonstrate that in the case of finite inflationary background...

50. Soft Metric Fluctuations during inflation

Kshitij Gupta

30/10/2024, 10:00

We use EFT techniques to show the all orders conservation of the super-horizon scalar and tensor modes during inflation. The EFT is built in analogy with Soft de Sitter EFT. Power counting and symmetry arguments are used to directly constrain the time evolution. We also introduce Mellin representation as an advantageous scheme to connect the UV and EFT descriptions.

31. Renormalization of the primordial inflationary power spectra

Silvia Pla Garcia (King's College London)

30/10/2024, 11:30

In this talk, I will explore the effects of renormalization on the amplitude of the inflationary spectra at scales measurable in the cosmic microwave background.

Via a gauge-invariant analysis, I will explain why the standard prediction for the spectra on superhorizon scales is a late-time attractor while they are UV finite at all times. This result is independent of the equation of state...

29. Bispectrum at 1-loop in the Effective Field Theory of Inflation

Supritha Bhowmick

30/10/2024, 11:50

We compute 1-loop corrections to the Bispectrum in the decoupling limit of the Effective Field Theory of Inflation (EFToI). We employ dimensional regularization to calculate the integrals and find that final results include structures of the form $\log{\left(\frac{H}{\mu}\right)}$, where $H$ is the Hubble parameter and $\mu$ is the renormalisation scale, and logarithms of ratios of comoving...

28. Slow-roll inflation at N3LO (as deviations from a purely de Sitter background)

Pierre Auclair (UCLouvain)

30/10/2024, 12:10

In the context of slow-roll inflation, deviations from a purely de Sitter background are expected and are both separate and complementary to the loop corrections in various inflationary scenarios. In this talk, I propose to go over some of the most up-to-date computations of the inflationary scalar and tensor slow-roll power spectra at next-to-next-to-next to leading order (N3LO), fully...

51. Physics of and from the large-scale structure of the Universe

Matthew Lewandowski

30/10/2024, 14:00

It is expected that measurements of the large-scale structure of the Universe will soon become our leading sources of fundamental cosmological information. In this talk, I will review some of the major progress, both theoretical and data-oriented, that we have made in understanding the physics of galaxy clustering, as well as what we might hope to learn about new physics (including primordial...

63. Discussion session

30/10/2024, 15:45

54. Stochastic inflation: key insights, latest advances and future directions

Chiara Animali

31/10/2024, 09:15

During inflation, quantum vacuum fluctuations are stretched beyond the Hubble radius, modifying the large-scale dynamics of the universe. Although typically negligible in the perturbative regime, this backreaction can become significant in regimes leading to primordial black hole (PBH) formation, where large density fluctuations arise, and which are the standard framework for addressing loop...

59. On the IR divergences in de Sitter: loops, resummation and the semi-classical wavefunction

Sebastian Cespedes

31/10/2024, 10:00

Detecting local Non-Gaussianity provides valuable insights into the early universe's particle composition. Interactions between the inflaton and light particles yield distinctive signatures, potentially observable in upcoming surveys. However, addressing IR divergences in light fields on de Sitter spacetimes requires careful treatment. Stochastic inflation offers a solution, but its...

22. IR finite correlation functions in de Sitter space, a smooth massless limit, and an autonomous equation

Polina Petriakova (Bologna U.)

31/10/2024, 11:30

Currently, the study of cosmological correlation functions is extremely favored, and a large number of new techniques are being developed. I will discuss a less-fashioned but very efficient technique to calculate the loop corrections to the correlation function in the long-wavelength approximation. By employing the Yang-Feldman-type equation, we compute the two-point correlation function up to...

21. One-loop infrared rescattering by enhanced scalar fluctuations during inflation

Sébastien Renaux-Petel

31/10/2024, 11:50

I will describe that, whenever the perturbations of some field are excited during inflation by a physical process on sub-horizon scales, they unavoidably generate, even through gravitational interactions alone, a significant resonant infrared cascade of power down to scales that are of the order of the horizon at that time. I will give general analytic one-loop results for the enhancement of...

47. On adiabatic renormalization with an infrared cut-off

Pietro Conzinu

31/10/2024, 12:10

We describe a new approach to renormalize physical quantities in curved space-time introducing a comoving infrared cut-off in defining the adiabatic counterpart of the physical quantity under consideration. This infrared cut-off is fundamental to avoid unphysical divergences that can be generated by a pathological behavior of the adiabatic subtraction extended to the infrared domain. Applying...

60. Late-time massless scalar field correlators in dS space from regions and effective field theory

Martin Beneke

31/10/2024, 14:00

I plan to discuss 1) what can be learnt from the interacting field in Euclidean dS space, 2) the method of region applied to calculate the late-time asymptotics from (IR-divergent) loop diagrams of the massless field, 3) matching to Soft dS Effective Theory.

61. New analytical results for massive inflationary correlators at tree and loop orders

Zhong-Zhi Xianyu

31/10/2024, 14:45

I will report a few new methods and results we recently obtained on the analytical computation of cosmological correlators with massive exchanges. At the tree level, we derive a complete set of differential equations for an arbitrary number of massive exchanges. We find a straightforward way to directly write down the analytical solution in terms of multivariate hypergeometric functions. The...

42. Thematic discussion 2

31/10/2024, 16:15

43. Thematic discussion 3

01/11/2024, 09:45

44. Thematic discussion 4

01/11/2024, 11:30