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We propose in this White Paper a concept for a space experiment using cold atoms to search for ultra-light dark matter, and to detect gravitational waves in the frequency range between the most sensitive ranges of LISA and the terrestrial LIGO/Virgo/KAGRA/INDIGO experiments. This interdisciplinary experiment, called Atomic Experiment for Dark Matter and Gravity Exploration (AEDGE), will also complement other planned searches for dark matter, and exploit synergies with other gravitational wave detectors. We give examples of the extended range of sensitivity to ultra-light dark matter offered by AEDGE, and how its gravitational-wave measurements could explore the assembly of super-massive black holes, first-order phase transitions in the early universe and cosmic strings. AEDGE will be based upon technologies now being developed for terrestrial experiments using cold atoms, and will benefit from the space experience obtained with, e.g., LISA and cold atom experiments in microgravity.KCL-PH-TH/2019-65, CERN-TH-2019-126

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We discuss modifications to the concept of an "antiparticle", induced by a breakdown of the CPT symmetry at a fundamental level, realized within an extended class of quantum gravity models. The resulting loss of particle-antiparticle identity in the neutral-meson system induces a breaking of the EPR correlation imposed by Bose statistics. The latter is parametrized by a complex parameter controlling the amount of contamination by the "wrong" symmetry state. The physical consequences are studied, and novel observables of CPT-violation in φ factories are proposed.PACS numbers: 11.30.Er; 13.25.Es; 03.65.UdThe CPT theorem is one of the most profound results of quantum field theory [1]. It is a consequence of Lorentz invariance, locality, as well as quantum mechanics (specifically unitary evolution of a system). One implication of CPT invariance is the equality of the masses between particles and antiparticles. In this respect, the best experimental tests of the CPT symmetry so far have been in the neutral Kaon system, where the equality of particle -antiparticle masses has been confirmed to better than one part in 10 17 [2]. However, this is not the end of the story, given that CPT violation may manifest itself in many subtle ways, thus motivating further experimental searches in various directions.The possibility of a violation of CPT invariance has been considered in a number of theoretical contexts that go beyond conventional local quantum field theory. In several models of quantum gravity (QG), for example, the axioms of quantum field theory, as well as conventional quantum mechanical behaviour, may not be maintained [3] in the presence of special field configurations, such as wormholes, microscopic (Planck size) black holes, and other topologically non-trivial solitonic objects, such as geons [4]. Such configurations are collectively referred to as space time foam, a terminology coined by J.A. Wheeler [5], who first conceived the idea that the structure of quantum space-time at Planckian scales (10 −35 m) may actually be fuzzy, characterised by a "foamy" nature. Given that such "objects" cannot be accessible to low-energy observers, it has been argued that a mixed state description must be employed (QG-induced decoherence) [3,6], "tracing" over them in the context of an effective field theory. In the case of microscopic black holes, for example, the decoherence arises due to the loss of information across microscopic event horizons, leading to complications in defining proper asymptotic statevectors and thus a Heisenberg scattering matrix. As a corollary of this, it has been argued [7] that, in general, CPT invariance in its strong form must be abandoned in quantum gravity. Since in such models the breakdown of the CPT symmetry happens at a fundamental level, it would imply that a proper CPT operator is ill defined. This in turn would lead to possible deviations from standard quantum mechanical evolution of states [8], which may not be necessarily associated with the mass difference between particle and antipar...

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Investigation at a φ-factory can shed light on several debated issues in particle physics. We discuss: i) recent theoretical development and experimental progress in kaon physics relevant for the Standard Model tests in the flavor sector, ii) the sensitivity we can reach in probing CPT and Quantum Mechanics from time evolution of entangled kaon states, iii) the interest for improving on the present measurements of non-leptonic and radiative decays of kaons and η/η′ mesons, iv) the contribution to understand the nature of light scalar mesons, and v) the opportunity to search for narrow di-lepton resonances suggested by recent models proposing a hidden dark-matter sector. We also report on the e + e − physics in the continuum with the measurements of (multi)hadronic cross sections and the study of γγ processes.

We calculate the density matrix for the decay of a polarised top quark into a polarised W boson and a massive b quark, for the most general W tb vertex arising from dimension-six gauge-invariant effective operators. We show that, in addition to the well-known W helicity fractions, for polarised top decays it is worth defining and studying the transverse and normal W polarisation fractions, that is, the W polarisation along two directions orthogonal to its momentum. In particular, a rather simple forward-backward asymmetry in the normal direction is found to be very sensitive to complex phases in one of the W tb anomalous couplings. This asymmetry, which indicates a normal W polarisation, can be generated for example by a P-odd, T-odd transition electric dipole moment. We also investigate the angular distribution of decay products in the top quark rest frame, calculating the spin analysing powers for a general W tb vertex. Finally we show that, using a combined fit to top decay observables and the tW cross section, at LHC it will be possible to obtain model-independent measurements of all the (complex) W tb couplings as well as the single top polarisation. Implications for spin correlations in top pair production are also discussed.