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We present a new framework to study the time variation of fundamental constants in a model-independent way. Model independence implies more free parameters than assumed in previous studies. Using data from atomic clocks based on 87 Sr, 171 Yb + and 133 Cs, we set bounds on parameters controlling the variation of the fine-structure constant, α , and the electron-to-proton mass ratio, µ . We consider variations on timescales ranging from a minute to almost a day. In addition, we use our results to derive some of the tightest limits to date on the parameter space of models of ultralight dark matter and axion-like particles.

In this brief paper, we show that atom interferometer experiments such as MAGIS, AION and AEDGE do not only have the potential to probe very light dark matter models, but will also probe quantum gravity. We show that the linear coupling of a singlet scalar dark matter particle to electrons or photons is already ruled out by our current understanding of quantum gravity coupled to data from torsion pendulum experiments. On the other hand, the quadratic coupling of scalar dark matter to electrons and photons has a large viable parameter space which will be probed by these atom interferometers. Implications for searches of quantum gravity are discussed.

Lorentz and CPT symmetry are among the deepest principles in all of physics. Yet, some theories attempting to unify quantum mechanics and gravity suggest that these symmetries may succumb to small violations detectable in high-precision experiments. The general framework enabling the search for violations of Lorentz and CPT symmetry is known as the Standard-Model Extension. Analyses based on this framework have led to hundreds of constraints on the coefficients for Lorentz violation. However, the strongly interacting sector of the SME remains comparatively unexplored. This thesis aims to address some of this unexplored terrain by considering Lorentz- and CPT-violating effects on quarks. As quarks are confined in hadrons, direct access to the coefficients modifying the propagation and interactions of quarks in hadrons is made possible by high-energy probes mediating lepton-hadron and hadron-hadron collisions. To study these collisions, a Lorentz- and CPT-violating version of the parton model is developed and investigated. The model is applied to deep inelastic scattering and the Drell-Yan process, resulting in real and simulated constraints using data from existing and future colliders.

We examine nonrenormalizable Lorentz- and CPT-violating effective operators applied to the quark sector of the Standard Model. Using Drell-Yan events collected by the ATLAS and CMS Collaborations, several constraints are extracted from time-independent modifications of the cross section on the \\(Z\\)-boson pole. The sensitivity to time-dependent modifications are also estimated by simulating a sidereal-time analysis. Our results suggest a dedicated search can improve on constraints from deep inelastic scattering by up to three orders in magnitude.

We discuss how grand unification can be probed with experiments at low energies using quantum sensors. Specifically, we show that scalar multiplets coupled to the gauge sector of a grand unified theory provide a mechanism for a time-varying unified coupling which has low-energy consequences which can be probed with quantum sensors. We then assume that the multiplets represent ultra light dark matter. Constraints on ultra light dark matter couplings to regular matter are extracted using atomic clock comparisons, pulsar timing arrays (NANOGrav) and MICROSCOPE.

In this brief paper, we show that atom interferometer experiments such as MAGIS, AION or AEDGE have the potential to not only probe very light dark matter models, but they will also probe quantum gravity. We show that the linear coupling of a singlet scalar dark matter particle to electrons or photons is already ruled out by our current understanding of quantum gravity coupled to data from torsion pendulum experiments. On the other hand, the quadratic coupling of scalar dark matter to electrons and photons has a large viable parameter space which will be probed by these atom interferometers. Implications for searches of quantum gravity are discussed.

We study the impact of general disformal metric transformations on fermions, which shift the gravitational metric by an additional rank-2 tensor. This tensor can in principle be constructed from scalar-field gradients, vector fields, or field-strength contractions. We show this transformation results in the conventional Dirac action being modified by additional kinetic and axial-current couplings that are quadratic in the shifted field. When the field sourcing the metric shift takes on a non-trivial background value, apparent Lorentz-violating effects can result, which we identify as terms in an effective field theory. Assuming the well-motivated cases of scalar and vector ultralight dark matter, we demonstrate that experimental tests of rotation and boost violation imply constraints on the additional kinetic coupling. Even under conservative assumptions, the constraints for vector ultralight dark matter are extremely stringent.

We present a new framework to study the time variation of fundamental constants in a model-independent way. Model independence implies more free parameters than assumed in previous studies. Using data from atomic clocks based on \\(^87\\)Sr, \\(^171\\)Yb\\(^+\\) and \\(^133\\)Cs, we set bounds on parameters controlling the variation of the fine-structure constant, \\(\\), and the electron-to-proton mass ratio, \\(\\). We consider variations on timescales ranging from a minute to almost a day. In addition, we use our results to derive some of the tightest limits to date on the parameter space of models of ultralight dark matter and axion-like particles.

We highlight the need for the development of comprehensive amplitude analysis methods to further our understanding of hadron spectroscopy. Reaction amplitudes constrained by first principles of \\(S\\)-matrix theory and by QCD phenomenology are needed to extract robust interpretations of the data from experiments and from lattice calculations.

Sir,--In reply to your of 16th inst., I would state, that to such as know me, it is not necessary to say that I am a republican of the old stamp, of the school of Jefferson.