CHEP

Pheno-Coffee Talk
2025-12-10 10:30 - 11:30 UTC
Speaker: Subhajit Ghosh (University of Texas at Austin, U.S.A.)
Date and time: Today, 10th December, Wednesday, at 10:30 a.m.
Venue: LH-3
Title: Probing $
u$-physics using cosmology
Abstract: In this talk, I will discuss new probes of neutrino interactions in cosmology, specifically using the cosmic microwave background (CMB). A phase shift in the acoustic oscillations of CMB spectra is a characteristic signature of the presence of non-photon species with a sound speed different from that of the photons. Focusing on neutrino self-interactions and dark matter neutrino interactions, I will demonstrate how these interactions imprint changes in the acoustic phase shift and can be probed using data. I will exhibit the potential of future CMB and 21-cm surveys to probe these interactions. I will also discuss models to realize strong neutrino self-interaction cosmology without violating stringent laboratory and BBN constraints.

Pheno-Coffee Talk
2025-12-10 14:30 - 15:30
Speaker: Sagnik Mondal (University of Maryland, U.S.A.)
Date and time: Today, 10th December, Wednesday, at 2:30 p.m.
Venue: LH-3
Title: A Simple Guide to Warm Inflation Model Building
Abstract: Inflaton couplings during warm inflation result in the production of a thermal bath. Thermal friction and fluctuations can dominate the standard de Sitter analogues, resulting in a modified slow-roll scenario with a new source of density fluctuations. Due to issues with back-reaction, it is advantageous to consider inflaton couplings with the thermal bath that are pseudo-scalar in nature, e.g., derivative interactions or topological $F tilde F$ couplings. We demonstrate that {it every single} existing model of warm inflation utilizing pseudo-scalar couplings needs to be corrected to properly account for all of the chemical potentials that the thermal bath acquires in response to the inflaton coupling. These chemical potentials are for non-conserved charges, and are non-zero only because of the applied inflaton couplings. The model-dependent chemical potentials modify the fluctuation-dissipation theorem, making the relationship between the thermal friction and thermal fluctuations model-dependent. In extreme cases, these chemical potentials can cause the friction term to vanish while thermal fluctuations remain non-zero. In the context of a simple example, we demonstrate how to calculate the chemical potentials, thermal friction, and thermal fluctuations using both the Boltzmann equations and by calculating thermal expectation values, showing explicitly that the two approaches give the same result.

Phenp-Coffee Talk
2025-12-11 14:30 - 15:30
Speaker: Vishal Singh Ngairangbam (Durham University, U.K.)
Date and time: Today, 11th December, Thursday, at 2:30 p.m.
Venue: LH-3
Title: Theory-priors for deep learning in collider phenomenology
Abstract: We live in an era of disruptive AI technologies, making waves in every domain, from business and technological applications to their usage across virtually every scientific discipline, including fundamental fields like mathematics and physics. This is primarily fueled by a class of neural networks popularly known as deep-learning algorithms, which efficiently leverage various domain knowledge (or inductive biases). In this talk, I’ll discuss these algorithms specifically in the context of collider phenomenology. We will first touch upon Convolutional Neural Networks (CNNs), a quintessential class of deep learning algorithms, and explore their relation to the structure of perturbative QCD radiation patterns. We will then discuss some of their drawbacks, which highlight the naturalness of the point cloud representation for jets and events. This representation allows for a direct connection between architecture design-principles and underlying first-principle requirements like infrared and collinear safety. Finally, we will move on to discussing the crucial role of symmetries (or equivariance in machine learning parlance) and their connection to the matrix-element method.

Pheno-Coffee Talk
2025-12-12 14:30 - 15:30
Speaker: Soumya Mukherjee (University of California at San Diego, U.S.A.)
Date and time: Today, 12th December, Friday, at 2:30 p.m.
Venue: LH-3
Title: Improved measurement of di-Higgs production in the four-b final state using Run-3 data collected by the CMS detector
Abstract: Significant progress has been achieved with LHC Run-2 data in probing the Higgs boson (H) self-interaction through searches for Higgs boson pair (HH) production. The strength of this self-interaction remains unmeasured, and its value has implications ranging from the long-term stability of the universe to possible manifestations of new physics. In this talk, I will present the most recent HH results in the four-b final state, based on 62 fb⁻¹ of early Run-3 data collected by the CMS detector during 2022 and 2023, covering both resolved and merged topologies. I will highlight the recent advancements and novel techniques employed to enhance the sensitivity of the analysis.
