DOE OSTI2019
The charge-parity-time (CPT) invariance principle and the weak equivalence principle (WEP) undergird our current understanding of Nature. CPT, which is based on only Lorentz invariance, locality, and spin-statistics, is basic to local relativistic quantum field theory (QFT) models of physical laws. Testing established principles like these is a long-standing and honorable tradition in physics. Beginning with Newton’s Laws, many firmly established laws have been superseded, often to the great surprise of contemporaneous physicists. Certainly, CPT rests on firmer grounds than the earlier widely believed, but erroneous principles, of parity (P) and charge-parity (CP) invariance, but this does not necessarily make CPT inviolable. Tests of CPT confront the entire framework of QFT, and are quite distinct from most other “beyond the Standard Model” searches, which look for new physics within the QFT framework. With the failure, so far, to find new physics at the LHC or in dark matter searches, the motivation to test QFT itself is urgent. The revolutionary consequences of CPT and WEP violation would be so great that these principles are under intense scrutiny in many different systems. Here we focus on tests of CPT and WEP that employ antimatter, specifically antihydrogen. Such tests are difficult to realize experimentally, but constitute some of the simplest and most profound matter-antimatter comparisons that can be performed. Antimatter particles have been investigated since the prediction and subsequent discovery of the positron in the 1930s. That early discovery motivated the search for the antiproton, culminating in its creation and detection in Berkeley two decades later. As far as we know today, particles and their antiparticles share identical properties except for the sign of their charge. Antihydrogen is the simplest antimatter system—it is the antiparticle of the simplest atom, hydrogen. Differences between the spectra of the two are forbidden by CPT. The weak equivalence principle (WEP), demands that matter and antimatter accelerate identically in a gravitational field. WEP has never been subjected to a direct, free fall test using antimatter. Because of the weakness of the gravita tional force, direct antimatter WEP tests must employ a neutral particle, of which antihydrogen is the simplest to obtain. There are reasons to suspect that something is amiss with our understanding of antimatter. All generally accepted theories of the Big Bang predict that roughly equal amounts of matter and antimatter should have been created. Instead, very little antimatter has been observed in the Universe. This baryogenesis problem is arguably the most fundamental issue with the theory of the Big Bang. Its resolution may come from the discovery of enhanced CP violation, but could also come from CPT or WEP violation.
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗