Snowmass White Paper: Precision Studies of Spacetime Symmetries and Gravitational Physics

Abstract

High-energy physics is primarily concerned with uncovering the laws and principles that govern nature at the fundamental level. Research in this field usually relies on probing the boundaries of established physics, an undertaking typically associated with extreme energy and distance scales. It is therefore unsurprising that particle physics has traditionally been dominated by large-scale experimental methods often involving high energies, such as colliders and storage rings, cosmological and astrophysical observations, large-volume detector systems, etc. The corresponding measurements are ideally suited for the discovery of new particles and interactions.However, high-sensitivity measurements in smaller experiments, often performed at lower energies, are presently experiencing a surge in importance for particle physics for at least two reasons. First, they exploit synergies to adjacent areas of physics with recent advances in experimental techniques and technology. Together with intensified phenomenological explorations, these advances have led to the realization that challenges associated with weak couplings or the expected suppression factors for new physics can be overcome with such methods while maintaining a large degree of experimental control. Second, many of these measurements broaden the range of particle-physics phenomena and observables relative to the above set of more conventional methodologies. Combining such measurements with the conventional efforts above therefore casts both a wider and tighter net for possible effects originating from physics beyond the Standard Model (BSM).The present work argues that this assessment points at a growing impact of such methods and measurements on high-energy physics, and it therefore warrants direct support as particle-physics research. More specifically, we discuss a sample of ongoing and future efforts in this context involving cold neutrons, a range of AMO-based studies, first-and higher-generation antimatter, and microscopic mechanical experiments including gravitationally entangled masses and optically levitated nanospheres. These efforts are poised to yield crucial insights into proposed BSM physics as diverse as novel short-range interactions, the small-scale structure of spacetime and in particular the fate of Lorentz, translation, CPT, CP, T, and P symmetries, the gravitational interaction of antimatter, certain quantum aspects of gravity, millicharged particles, gravitationalwave measurements, and dark matter. These synergies and their prospective physics output foreshadow a promising future for such types of experimental and theoretical activities. Leveraging the recent rapid progress and bright outlook associated with such studies for high-energy physics, could yield high returns, but requires substantial and sustained efforts by funding agencies.

Detection of early-universe gravitational-wave signatures and fundamental physics

“…More generally, GUT symmetry breaking chains more often than not allow for observable signals from some set of defects [50]. 2 Searches for proton decay provide a complimentary probe of symmetry breaking chains, as chains that allow for proton decay can be chains that do not predict strings [373,374]. Furthermore, there has been a growing interest in GWs from global/axion topological defects due to the close connection to axion or axion-like (ALP) dark matter physics [323,337,348,349,375,376]: when PQ symmetry breaking occurs after inflation, these topological defects are an indispensable companion of axion particles.…”

“…section 9.4 of [549]), while for Type-I, LISA will be able to explore parameter regions beyond the LHC. Extension of the SM by a (real) scalar SU (2) L triplet. This scenario [145,147,148,550], which entails adding three new degrees of freedom to the SM, allows for a very and Higgs portal coupling a 2 .…”

“…(Snowmass white paper "Future Gravitational-Wave Detector Facilities" [1] gives an extensive survey of planned and proposed GW observatories. Snowmass white paper "Spacetime Symmetries and Gravitational Physics" [2] provides an overview of highsensitivity small experiments that can be used for GW detections. )…”

Lorentz symmetry breaking -- classical and quantum aspects

“…Further, in [203], a methodology allowing for estimation of LV parameters from observations of gravitational waves was presented, and it was claimed in this paper that this analysis is currently on the way. The most recent results of various experiments on Lorentz and CPT breaking, both in flat and curved spacetime, can be found in [204].…”

Effective field theories of gravity and compact binary dynamics: A Snowmass 2021 whitepaper

“…It is therefore fair to say that, at least in the context of flat spacetime, the IR behavior of quantum gravity is well under theoretical control. Of course, the predictions of this theory will not be tested experimentally any time soon [17], e.g. for test masses separated by a distance of r ∼ 1 mm, the corrections to the classical potential from Eq.…”