Particle Physics

The LHC bear great potential in seeking for hidden sector particles, such as a high-quality QCD axion, glueballs, and heavy neutrinos. 

In this talk, I will present my recent studies on how to probe these hidden sector particles through the novel but challenging long-lived particle searches.

The central idea of the bootstrap philosophy is to constrain observables directly from consistency conditions alone, bypassing the intricacies of the Lagrangian formalism. In this talk, I will adopt this viewpoint and describe a boundary-centric approach to determine cosmological correlators, following a perspective familiar from the modern studies of scattering amplitudes. Specifically, I will describe the symmetries and singularities of three- and four-point functions in de Sitter space and inflation, and explain how these principles can be used to fully determine the final answer without reference to bulk time evolution. I will also highlight spectroscopic features encoded in these correlators, relevant for the search of primordial non-Gaussianity in future cosmological observations.

I will describe how current and upcoming 21-cm measurements during cosmic dawn can probe a plethora of dark-matter and dark-energy models. This era saw the formation of the first stars, which coupled the spin temperature of hydrogen to its kinetic temperature---producing 21-cm absorption. The depth of this absorption acts as a thermostat, allowing us to constrain exotic cooling or heating due to dark matter. Additionally, the timing of the 21-cm signal strongly depends on the abundance of the small minihalos that hosted the first stars, allowing us to tightly constrain dark-matter models with suppressed power, such as warm or fuzzy dark matter. Finally, I will describe how in LCDM the acoustic physics of recombination are imprinted onto the 21-cm power spectrum during cosmic dawn, resulting in robust velocity-induced acoustic oscillations (VAOs). These act as a new standard ruler at z~20, opening up searches for early dark energy and perhaps resolving the H0 tension.

milliQan is a proposed search for milli-charged particles produced at the LHC with expected sensitivity to charges of between 0.1e and 0.001e for masses in 0.1 - 100 GeV range. The proposed detector is an array of 4 stacks of 60 cm long plastic scintillator arrays read out by PMTs. It will be installed in an existing tunnel 33 m from the CMS interaction point at the LHC, with 17 m of rock shielding to suppress beam backgrounds. In the fall of 2017 a 1% scale “demonstrator” of the proposed detector was installed at the planned site in order to study the feasibility of the experiment, focusing on understanding various background sources such as radioactivity of materials, PMT dark current, cosmic rays, and beam induced backgrounds. In this talk I will discuss the general concept of the experiment, the results from the demonstrator, and the plan for the future.

Detecting light dark matter that interacts weakly with electromagnetism has recently become one of the benchmark goals of near-term and futuristic direct detection experiments. In this talk, I will discuss an alternative technique to directly detecting such particles below the GeV-scale. The approach involves distorting the local flow of dark matter with time-varying fields and measuring these distortions with shielded resonant detectors, such as LC circuits.

Non minimal couplings of scalar fields to gravity are a generic feature of Lagrangian formulations of gravity. Although challenging to probe at low energies and small curvature, such couplings can play a crucial role in cosmological setups. We focus on their impact in the production of scalar dark matter and its interplay with inflationary physics. We show how the standard non-thermal production mechanism of scalar dark matter, the misalignment mechanism, is modified, and explore how alternative scenarios like production from inflationary fluctuations become viable. We study potentially observable features of these scenarios, such as the enhancement of dark matter substructure at small scales and the generation of an isocurvature component in the fluctuations of the CMB.

Query complexity is a common tool for comparing quantum and classical computation, and it has produced many examples of how quantum algorithms differ from classical ones. Here we investigate in detail the role that oracles play for the advantage of quantum algorithms. We do so by using a simulation framework, Quantum Simulation Logic (QSL), to construct oracles and algorithms that solve some problems with the same success probability and number of queries as the quantum algorithms. The framework can be simulated using only classical resources at a constant overhead as compared to the quantum resources used in quantum computation. Our results clarify the assumptions made and the conditions needed when using quantum oracles. Using the same assumptions on oracles within the simulation framework we show that for some specific algorithms, such as the Deutsch-Jozsa and Simon’s algorithms, there simply is no advantage in terms of query complexity. This does not detract from the fact that quantum query complexity provides examples of how a quantum computer can be expected to behave, which in turn has proved useful for finding new quantum algorithms outside of the oracle paradigm, where the most prominent example is Shor’s algorithm for integer factorization.

It has been recently pointed out that variable weak gravitational lensing effects on the motion of background stars can be used to probe nonluminous structures inside the Milky Way halo. I will describe one possible detection strategy targeting collapsed dark matter structures in the mass range from million to billion solar masses. The data analysis technique will be discussed in detail with an application to the second data release of Gaia.

We propose a novel design of a laboratory search for axions based on photon regeneration with superconducting RF cavities. Our particular setup uses a toroid as a region of confined static magnetic field, while production and detection cavities are positioned in regions of vanishing external field. This permits cavity operation at quality factors of Q ~ 10¹⁰ - 10¹². The limitations due to fundamental issues such as signal screening and back-reaction are discussed, and the optimal sensitivity is calculated. This experimental design can potentially probe axion-photon couplings beyond astrophysical limits, comparable and complementary to next generation optical experiments.

The stability of dark matter and its interactions with the Standard Model remain some of the biggest mysteries of our time. Instead of inventing ad hoc stabilization symmetries I propose to economically use the existing baryon and lepton number symmetries of the SM. This can lead to interesting signatures in terrestrial experiments, shower us in anti-helium, and keep neutron stars warm.

One of the leading hypotheses for dark matter is that it consists of bosonic particles with masses below the eV scale, such as axions, moduli and dark photons. Unlike spin-0 particles, spin-1 particles do not have a misalignment mechanism to produce the desired abundance of dark matter, and population of light dark photon dark matter has been an open question in cosmology. I will present a novel mechanism to produce light spin-1 dark matter in cosmology. The dark matter energy density is initially stored in an axion-like field which is misaligned from its minimum during inflation. This energy density is efficiently transferred to dark photons using tachyonic particle production. This mechanism opens up extensive parameter space for dark photon dark matter.