Particle Physics

Hidden sectors are motivated by a range of phenomena unexplained by the Standard Model, such as dark matter, neutrino masses, and the baryon asymmetry. Hidden sector particles below the weak scale can be copiously produced at high-energy and intensity-frontier experiments, but may have evaded detection with current searches.
I will discuss new searches I am doing with the BaBar collaboration that are probing unexplored, well-motivated territory for hidden sectors. I will also show how signatures such as displaced vertices motivate comprehensive, complementary searches at low- and high-energy experiments.

New scalar bosons that are uncharged under the Standard Model have many phenomenological applications, and in particular may serve as mediators between the dark and visible sectors. Such scalars are often taken to have Higgs-like couplings to Standard Model fermions, in order to evade constraints from bounds on flavor-changing neutral currents.
We describe an alternative approach, based on an effective field theory approach in which a new scalar preferentially couples to a single fermion mass eigenstate. In such theories, we show through a spurion analysis that small flavor changing couplings are still technically natural. Examples of our framework include a muon-philic scalar that can explain the observed anomalous magnetic moment of the muon and an up-specific scalar mediator to a dark sector, whose phenomenologies we discuss in detail.

In recent years the Standard Model Effective Field Theory (SMEFT) has emerged as a well defined and systematically improvable theory to study the constraints on physics beyond the Standard Model. This formalism explains old mysteries in interpreting LEP data and offers a field theory framework to combine such data with LHC measurements of the properties of the Higgs. We discuss the current status of these combined studies. The lack of evidence for new physics resonances at LHC has also encouraged new approaches to explaining the observed value of the electroweak scale, in the presence of physics beyond the Standard Model. One such approach is the Neutrino Option, that generates the electroweak scale from an underlying Majorana scale, when Neutrino masses come about due to a seesaw mechanism. We discuss how this approach is embedded into the SMEFT.

Repeated null-results at dark matter experiments targeted at WIMP masses, have resulted in the spotlight shifting to lighter dark matter and more exotic WIMP candidates. In this talk I shall present the rich level structure of molecules and nuclei as a tool to explore MeV scale dark matter and dark forces. I will also present a novel detector concept that supplies energy to dark matter, thus accessing inelastic dark matter parameter space.

Among the many candidates proposed to explain the nature of Dark Matter, WIMPs have been the most supported in the last decades, because of their success in a natural explanation of the current Dark Matter abundance and their ubiquitous presence in models addressing the hierarchy problem.
Other candidates that have been attracting some attention recently are Primordial Black Holes, which would have formed in the early history of the universe.
In my talk I will touch on both frameworks for the explanation of Dark Matter.
As for WIMP candidates, I will discuss the interplay between their experimental searches and theoretical frameworks. On the side of Effective Field Theories, I propose a method to use them consistently for the recast of collider searches. On the side of simplified models, in the presence of apparent gauge anomalies at low energies I highlight the enhanced reach of indirect searches.
In the last part I will illustrate a model for the generation of PBHs relying on a feature already present in the Standard Model, the metastability of the Higgs vacuum. Another signature of this remarkable property of the SM could be the generation of a background of gravitational waves.
The observation of either of these signatures would represent a spectacular confirmation of the metastability of the Higgs vacuum.

We perform a full (3+1)-dimensional numerical simulation of the axion field around the QCD epoch. Our aim is to fully resolve large dynamical non-linear effects in the inhomogenous axion field. These effects are important as they lead to large overdensities in the field at late times. Those overdensities will eventually evolve into axion minicluster, which have various phenomenological implications like microlensing events. It is therefore important to have a reliable estimate of the number of overdensities and their mass relation.

After the detection of black hole and neutron star binary mergers at LIGO/Virgo, gravitational wave becomes a new observational channel that we didn't have access to years ago.

It is an interesting question to ask what kind of new particle physics this channel can probe.

To answer this question, one needs to fill the gap between the scales of the astrophysical processes and the fundamental structures.

In this talk, I will demonstrate a few ways of extracting particle physics information directly from binary merger events of neutron stars and boson stars, and using this information to constrain well motivated dark sectors, including dark gauge boson and axion like particles.

An outline of future directions will also be discussed.

Recent progress in determining scattering phase shifts, and hence, resonance properties from lattice QCD in finite volumes is presented.

The relationship between finite-volume stationary-state energies and the two-particle scattering K-matrix is discussed.

Details of the Monte Carlo computations of the finite-volume two-particle energies are described.

Results for pion-pion, kaon-pion, and nucleon-pion scattering are presented.

Most current dark matter detection strategies, including both direct and indirect efforts, are based on the assumption that the galactic dark matter number density is quite high, allowing for the detection of rare scattering events. Such a paradigm arises naturally if the dark matter self-interactions are weak. However, strong interactions within the dark sector can give rise to large composite objects, whose detection requires a different experimental paradigm. We call these object Dark Blobs. In such theories, the energy transfer due to a single collision with a Standard Model particle tends to be small, below the energy threshold of many nuclear recoil experiments. Fortunately, due to their exponentially large composite nature, the interactions between these objects and a terrestrial detector can be coherently enhanced. Therefore, while the effect on a single probe is small, the large collective effect can be quite dramatic and, importantly, above experimental thresholds. In this talk, I will briefly motivate the early Universe formation of certain types of Dark Blobs and then focus on multiple detection avenues for these objects.

We present a new solution to the Hierarchy Problem utilizing non-linearly realized discrete symmetries. The cancelations occur due to a discrete symmetry that is realized as a shift symmetry on the scalar and as an exchange symmetry on the particles with which the scalar interacts. We show how this mechanism can be used to solve the Little Hierarchy Problem as well as give rise to light axions.

The power spectrum for fluctuations in the number density of galaxies can be very different in shape from the power spectrum for fluctuations in the mass density at very small wave vectors (i.e., large length scales) if the primordial density fluctuations are non-Gaussian. I review this phenomena. (It  is fairly well known in the more astrophysical part of the cosmology community but less so in the particle physics part of the field.) Then I show that primordial non-Gaussianities that arise from quantum loop diagrams in de-Sitter space can give rise to this phenomena. I also discuss if it is observable given constraints on primordial non-Gaussianity that arise from the Cosmic Microwave Background

We present fundamental limits of axion and hidden-photon dark matter searches probing the electromagnetic coupling.  These limits are informed by constraints on noise in phase-insensitive amplifiers, as well as constraints on impedance matching. We motivate the use of quantum-limited amplifiers for dark matter searches, in particular at low masses/frequencies, where they provide a substantial enhancement due to sensitivity outside of the detector bandwidth. We discuss the role of priors, e.g. direct detection and astrophysical constraints, in optimizing scan strategies and comparing receiver architectures. We show that the figure of merit for wideband dark matter searches is the integrated sensitivity of the receiver circuit, and that the integrated sensitivity is constrained by the Bode-Fano criterion. The optimized single-pole resonator read out by a quantum-limited amplifier is close to the Bode-Fano limit, establishing such a search technique as a fundamentally near-ideal setup for dark matter measurement. We discuss the implications of these broad optimization statements for DM Radio, a lumped-element search for axion and hidden-photon dark matter operating in the 100 Hz (~0.5 peV)- 300 MHz (~1 ueV) range. Our results strongly motivate the use of quantum measurement techniques (e.g. squeezing, entanglement, photon counting, backaction evasion), which evade the limits, in future dark matter searches.