Advances in atomic physics, such as cooling and trapping of atoms and molecules and developments in frequency metrology, have added orders of magnitude to the precision of atom-based clocks and sensors. Applications extend beyond atomic physics and this article reviews using these new techniques to address important challenges in physics and to look for variations in the fundamental constants, search for interactions beyond the standard model of particle physics, and test the principles of general relativity.

Search for New Physics with Atoms and Molecules

We investigate unparticle effects in ${B}_{s}$-${\overline{B}}_{s}$ mixing. In particular we discuss the possibility of reproducing the experimental result of $\ensuremath{\Delta}{M}_{s}$, while having large effects on the mixing phase ${\ensuremath{\phi}}_{s}$, which might be visible in current experiments.

Unparticle physics effects in B s - B ¯ s mixing

Many particle-physics models that extend the standard model predict the existence of long-range spin-spin interactions. We propose an approach that uses the Earth as a polarized spin source to investigate these interactions. Using recent deep-Earth geophysics and geochemistry results, we create a comprehensive map of electron polarization within the Earth induced by the geomagnetic field. We examine possible long-range interactions between these spin-polarized geoelectrons and the spin-polarized electrons and nucleons in three laboratory experiments. By combining our model and the results from these experiments, we establish bounds on torsion gravity and possible long-range spin-spin forces associated with the virtual exchange of either spin-one axial bosons or unparticles.

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Using the Earth as a polarized electron source to search for long-range spin-spin interactions.

We show that scalar unparticles coupled to the Standard Model Higgs at the renormalizable level can have a dramatic impact in the breaking of the electroweak symmetry already at tree level. In particular one can get the proper electroweak scale without the need of a Higgs mass term in the Lagrangian. By studying the mixed unparticle-Higgs propagator and spectral function we also show how unparticles can shift the Higgs mass away from its Standard Model value, \lambda v^2, and influence other Higgs boson properties. Conversely, we study in some detail how electroweak symmetry breaking affects the unparticle sector by breaking its conformal symmetry and generating a mass gap. We also show that, for Higgs masses above that gap, unparticles can increase quite significantly the Higgs width.

Unparticles-Higgs Interplay

Coupling the scale invariant unparticle sector to flavor physics and assuming that it remains scale invariant I investigate its consequences in heavy flavor physics. A characteristic feature of unparticle physics is a $CP$-even phase leading to novel $CP$ violating phenomena. The phase is large, based on the assumption that the unparticle sector is strongly self-coupled. I consider the $CP$ asymmetry in the leptonic decay ${B}^{+}\ensuremath{\rightarrow}{\ensuremath{\tau}}^{+}\ensuremath{\nu}$ and the hadronic decay ${B}_{d}\ensuremath{\rightarrow}{D}^{+}{D}^{\ensuremath{-}}$, taking into account constraints of branching ratios and time dependent $CP$ asymmetries. It turns out that the $CP$ asymmetry can be very large even for small couplings because the unparticle interaction term has a lower scaling dimension than the four-Fermi weak interaction term. $CP$ asymmetries in leptonic decays such as ${B}^{+}\ensuremath{\rightarrow}{\ensuremath{\tau}}^{+}\ensuremath{\nu}$ are neither experimentally searched for nor predicted by any other model. I show that the novel $CP$ violation is consistent with the $CPT$ theorem. I identify the $CP$ compensating mode in the unparticle sector and explicitly demonstrate the exact cancellation as demanded by the $CPT$ theorem.

Unparticles at heavy flavour scales: CP violating phenomena

Unparticles as suggested by Georgi are identities that are not constrained by dispersion relations but are governed by their scaling dimension d. Their coupling to particles can result in macroscopic interactions between matter that are generally an inverse nonintegral power of distance. This is totally different from known macroscopic forces. We use the precisely measured long-ranged spin-spin interaction of electrons to constrain unparticle couplings to the electron. For 1<d<1.5 the axial vector unparticle coupling is excluded, and for 1<d<1.3 the pseudoscalar and vector couplings are also ruled out. These bounds and the ones for other ranges of d exceed or are complementary to those obtained previously from exotic positronium decays.

Ji-Yuan Liu

Papers

Long-range electron spin-spin interactions from unparticle exchange.