High Energy Physics

From dark matter to the strong CP problem to the dynamics behind the weak scale, a variety of observations make for a compelling case that the Standard Model is an incomplete description of subatomic physics. Yet none of these puzzles provides unambiguous guidance on how we should proceed to find what comes next.

I will argue that this state of affairs calls for a multi-directional strategy in our quest for physics Beyond-the-Standard-Model. Only a combination of new theoretical developments and original ideas, confronted with the vast array of experiments at our disposal, will provide us with the big picture we need to move beyond.

In recent years quantum error correction(QEC) has become an important part of AdS/CFT. Unfortunately, there are no field-theoretic arguments about why QEC holds in known holographic systems. The purpose of this paper is to fill this gap by studying the error-correcting properties of the fermionic sector of various large N theories. Specifically, we examine SU(N) matrix quantum mechanics and 3-rank tensor O(N)^3 theories. Both of these theories contain large gauge groups. We argue that gauge singlet states indeed form a quantum error-correcting code. Our considerations are based purely on large N analysis and do not appeal to a particular form of Hamiltonian or holography. Based on: arXiv: 2008.12869

Models of Dark Matter (DM) can leave unique imprints on the Universe's small scale structure by boosting density perturbations on small scales. We study the capability of Pulsar Timing Arrays to search for, and constrain, subhalos from such models. The models of DM we consider are ordinary adiabatic perturbations in ΛCDM, QCD axion miniclusters, models with early matter domination, and vector DM produced during inflation.

If we live in a supersymmetric world, SUSY has to be broken at some (high) scale. I will show how the presence of a SUSY-breaking hidden sector can lead to gravitational wave (GW) signals at future interferometers. I will focus on first order phase transitions that can occur along the pseudomodulus universally related to SUSY breaking. Current bounds on the superpartners are compatible with GW signals at future interferometers, while the observation of a GW signal from a SUSY-breaking hidden sector would imply superpartners within the reach of future colliders.  Along the way, I will analyze the new field theoretical features of the phase transition along the pseudomodulus direction. These allow us to pinpoint what are the necessary requirements for a SUSY-breaking hidden sector to lead to strong GW signals.

Analog quantum simulation has the potential to be an indispensable technique in the investigation of complex quantum systems. In this work, we numerically investigate a one-dimensional, faithful, analog, quantum electronic circuit simulator built out of Josephson junctions for one of the paradigmatic models of an integrable quantum field theory: the quantum sine-Gordon (qSG) model in 1+1 space-time dimensions. We analyze the lattice model using the density matrix renormalization group technique and benchmark our numerical results with existing Bethe ansatz computations. Furthermore, we perform analytical form-factor calculations for the two-point correlation function of vertex operators, which closely agree with our numerical computations. Finally, we compute the entanglement spectrum of the qSG model. We compare our results with those obtained using the integrable lattice-regularization based on the quantum XYZ chain and show that the quantum circuit model is less susceptible to corrections to scaling compared to the XYZ chain. We provide numerical evidence that the parameters required to realize the qSG model are accessible with modern-day superconducting circuit technology, thus providing additional credence towards the viability of the latter platform for simulating strongly interacting quantum field theories. 

Axion cosmic strings have for some time been considered a potential source of enhancement of axion dark matter production, and have been the subject of extensive simulations (for references, see out in recent years).  But axion strings are rather peculiar entities.  This talk will explore some aspects of these objects, and suggest that they are not likely to play a distinguished role in early universe cosmology.

Detection mechanisms for low mass bosonic dark matter candidates, such the axion or hidden photon, leverage potential interactions with electromagnetic fields, whereby the dark matter (of unknown mass) on rare occasion converts into a single photon. Current dark matter searches operating at microwave frequencies use a resonant cavity to coherently accumulate the field sourced by the dark matter and a near standard quantum limited (SQL) linear amplifier to read out the cavity signal. To further increase sensitivity to the dark matter signal, sub-SQL detection techniques are required. Here we report the development of a novel microwave photon counting technique and a new exclusion limit on hidden photon dark matter. We operate a superconducting qubit to make repeated quantum non-demolition measurements of cavity photons and apply a hidden Markov model analysis to reduce the noise to 15.7 dB below the quantum limit, with overall detector performance limited by a residual background of real photons. With the present device, we perform a hidden photon search and constrain the kinetic mixing angle to  ≤ 1.68×10−15 in a band around 6.011 GHz (24.86 μeV) with an integration time of 8.33 s. This demonstrated noise reduction technique enables future dark matter searches to be sped up by a factor of 1300. By coupling a qubit to an arbitrary quantum sensor, more general sub-SQL metrology is possible with the techniques presented in this work.