Scientific Series

I will discuss a set of calculations of dark matter interactions with low threshold semi-conductor detectors such as SENSEI and superCDMS. As a warm-up, I'll show how to rephrase traditional DM-electron scattering calculations in terms of the energy loss function of the material. We will then apply this framework to compute the rate for the Migdal effect in semi-conductor targets. This is needed because the traditional calculations of the Migdal effect do not apply in low threshold semi-conductor detectors, as the delocalized nature of the valence electrons is not taken into account.

Although cold dark matter (CDM) has been established, this is only the case for measurements at large scales, which are larger than galaxy-sized structures. Even though we need to understand the important role of baryonic components, matter distribution at small scales can be the key to distinguishing different particle dark matter candidates. In fact, warm dark matter, self-interacting dark matter, and fuzzy dark matter have been proposed, yielding different matter distributions at sub-galactic scales. These small-scale distributions have been studied with numerical simulations. Whereas very reliable, numerical simulations suffer certain issues. They are limited by both numerical resolution and shot noise. They tend to take a lot of computational time. These might be a bottleneck for surveying through multi-dimensional parameter space of various dark matter models. I present semi-analytic models of small-scale structure, especially dark matter subhalos, which are based on structure formation theory and the tidal evolution of subhalos. Our models for CDM have been well tested against the results of various numerical simulations. The semi-analytic models are free from all the problems of the numerical simulations mentioned above. Therefore, they might be essential ingredients for identifying the particle nature of dark matter through gravitational (lensing, pulsar timing), astrophysical (satellite counts, stellar streams), and astroparticle probes (gamma rays).

The spacetime in the interior of a black hole can be described by an homogeneous line element, for which the Einstein–Hilbert action reduces to a one-dimensional mechanical model. We have shown that this model exhibits a symmetry under the (2+1)-dimensional Poincaré group. The existence of this symmetry provides a powerful criterion to discriminate between different regularization and quantization schemes. It also unravels new aspects of symmetry for black holes, and opens the way towards a rigorous group quantization of the interior. Remarkably, the physical ISO(2,1) symmetry can be seen as a broken infinite-dimensional symmetry. This is done by reinterpreting the action for the model as a geometric action for the BMS3 group, where the configuration space variables are elements of the algebra bms3 and the equations of motion transform as coadjoint vectors.

Zoom Link: https://pitp.zoom.us/j/99646733321?pwd=U05kYU85V0Q4VCtrZ1BNV2JZbE1DUT09

We consider quantum field theory on a rigid de Sitter space. We show that the perturbative expansion of late-time correlation functions to all orders can be equivalently generated by a non-unitary Lagrangian on a Euclidean AdS geometry. We use this to infer the analytic structure of the spectral density that captures the conformal partial wave expansion of a late-time four-point function, to derive an OPE expansion, and to constrain the operator spectrum. Generically, dimensions and OPE coefficients do not obey the usual CFT notion of unitarity. Instead, unitarity of the de Sitter theory manifests itself as the positivity of the spectral density. We illustrate and check these properties by explicit calculations in a scalar theory by computing first tree-level, and then full one-loop-resummed exchange diagrams.

The epoch of cosmic reionization can be probed using the secondary anisotropies imprinted on the cosmic microwave background (CMB) temperature and polarization field. I will discuss the imprints of patchy reionization on the kSZ power spectrum and CMB B-mode polarization. I will introduce two new scaling relations to connect the kSZ and secondary B-mode power spectrum with the physics of reionization. I will discuss the advantage of a joint study of the kSZ signal and secondary B-mode polarization from the ongoing/upcoming CMB experiments to get a better understanding of the epoch of reionization.

The inclusion of the cosmological constant is one of the main questions faced by quantum gravity. In three dimensions, non-perturbative approaches to quantum gravity including loop quantum gravity (LQG),  combinatorial quantization and  spinfoam path integrals encode the cosmological constant as a deformation parameter in a quantum group structure. In this talk, I will focus on the LQG approach: I will explain the Poisson-Lie structure of the classical phase space and how its quantization naturally leads to the emergence of quantum groups. I will use the holonomy-flux algebra and its spinorial presentation introduced in the series of work by Bonzom, Dupuis, Girelli, Livine and myself. This allows to construct the Hamiltonian constraint, understand its matrix elements as Turaev-Viro amplitudes. This connects LQG to the other approaches in a unified mathematical setting.

Several anomalies have been recently reported by different laboratory experiments: the flavor anomalies involving B meson semileptonic and leptonic decays by the LHCb and B-factories, as well as the anomalous muon (g-2) by the Fermilab (g-2) collaboration. These deviations, if not coming from underestimated experimental or theoretical uncertainties, are pointing to new degrees of freedom around the few TeV scale. Enlarging the field content of the Standard Model may lead to baryon number violation, whose aggressive experimental constraints can rule out a wide range of attractive candidates. Motivated by its safeness under unacceptable baryon number violation and the possibility for having TeV scale physics, I will introduce the simplest theory for matter (leptons-quarks) unification based on the Pati-Salam symmetry and show how this theory can address both the flavor anomalies and the muon (g-2) with the scalar leptoquarks that it predicts.

Zoom Link: https://pitp.zoom.us/j/95090784229?pwd=Q21oQUVkeXFiSmt5S3hKcGJ3SlEyZz09

A high energy muon collider complex can provide new and complementary discovery potential to the LHC or future hadron colliders. New spin-1 bosons are a motivated class of exotic new physics models. In particular leptoquarks, dark photons, and Lμ — Lτ models have distinct production channels at hadron and lepton machines. We study a vector leptoquark model at a muon collider with √ s = 3, 14 TeV within a set of both UV and phenomenologically motivated flavor scenarios. We compute which production mechanism has the greatest reach for various values of the leptoquark mass and the coupling between leptoquark and Standard Model fermions. We find that we can probe leptoquark masses up to an order of magnitude beyond √ s with perturbative couplings. Additionally, we can also probe regions of parameter space unavailable to flavor experiments. In particular, all of the parameter space of interest to explain recent low-energy anomalies in B meson decays would be covered even by a √ s = 3 TeV collider. We also consider other applications of a muon collider complex in the hunt for new physics.

Zoom link:  https://pitp.zoom.us/j/97081554839?pwd=bFBmdUExV0VSdm4vcm5iMTVtaTFrUT09

Cosmic strings arise as remnants of phase transitions in the early Universe, often related to theories of grand unification (GUTs). If such a phase transitions occurs at high energies, the resulting cosmic string network generates a sizable amount of gravitational waves. Most work so far has focused on the gravitational wave signal from topologically stable cosmic strings. In this talk I will introduce metastable cosmic strings, which are a generic consequence of many GUTs. I will discuss how this idea can be probed in various ongoing and upcoming gravitational wave experiments, from pulsar timing arrays to space- and ground-based interferometers. In the final part of my talk I will discuss a recent proposal on using the radio telescopes to probe this and other sources of ultra high frequency gravitational waves.

Strong gravity tests indicate that general relativity is a very accurate description of the classical dynamics of spacetime even at extreme regimes. Yet, the same dynamics can be described by "alternative" versions of general relativity such as unimodular gravity. In the quest for a quantum theory of the gravitational field, it is unclear if the quantization of such classically equivalent theories leads to the same physical predictions. In this talk, I will report on some recent results regarding this issue in the framework of continuum and perturbative quantum field theory. With a view towards ultraviolet completion, I will discuss some evidence for asymptotic safety in unimodular quantum gravity. Moreover, I will comment on the role of matter fields which couple very differently to gravity in those settings.   

If dark matter is composed at least partially of primordial black holes (PBHs) then structure formation occurs very differently than in standard particle dark matter scenarios.  PBH binaries, halos and other structures can form at very early redshifts and the resulting nonlinear dynamics can change constraints on the abundance of PBHs.  In this talk I will describe this structure formation history using results from cosmological simulations and discuss constraints on solar mass and heavier PBHs from LIGO and the CMB.  Lastly, I will discuss how the baryons may be impacted by such nonlinear structures.