Yue-Liang Wu

Sommerfeld enhancements with vector, scalar and pseudoscalar force-carriers

The first AMS-02 measurement confirms the existence of an excess in the cosmic-ray positron fraction previously reported by the PAMELA and Fermi-LAT experiments. If interpreted in terms of thermal dark matter (DM) annihilation, the AMS-02 result still suggests that the DM annihilation cross section in the present day should be significantly larger than that at freeze-out. The Sommerfeld enhancement of the DM annihilation cross section is a possible explanation, which is however subject to the constraints from DM thermal relic density, mainly due to the annihilation of DM particles into force-carrier particles introduced by the mechanism. We show that the effects of the Sommerfeld enhancement and the relic density constraints depend significantly on the nature of the force carrier. Three scenarios where the force carrier is a vector boson, scalar, and pseudoscalar particle are investigated and compared. The results show that for the case with a vector force carrier, the Sommerfeld enhancement can marginally account for the AMS-02 data for the DM particle annihilating into 2 mu final states, while for the scalar force carrier the allowed Sommerfeld enhancement factor can be larger by a factor of 2. For the case with a pseudoscalar force carrier, the Sommerfeld enhancement factor can be very large in the resonance region, and it is possible to accommodate the AMS-02 and Fermi-LAT result for a variety of DM annihilation final states.

Enhancement of dark matter relic density from late time dark matter conversions

We demonstrate that if the dark matter (DM) in the Universe contains multiple components, the possible interactions between the DM components may convert the heavier DM components into lighter ones. It is then possible that the lightest DM component with an annihilation cross section significantly larger than that of the typical weakly interacting massive particle (WIMP) may lead to a relic density in agreement with cosmological observations, due to an enhancement of number density from the DM conversion process at late time after the thermal decoupling. This may provide an alternative source of boost factor relevant to the positron and electron excesses reported by the recent DM indirect search experiments.

Consistency and advantage of loop regularization method merging with Bjorken–Drell’s analogy between Feynman diagrams and electrical circuits

The consistency of loop regularization (LORE) method is explored in multiloop calculations. A key concept of the LORE method is the introduction of irreducible loop integrals (ILIs) which are evaluated from the Feynman diagrams by adopting the Feynman parametrization and ultraviolet-divergence-preserving (UVDP) parametrization. It is then inevitable for the ILIs to encounter the divergences in the UVDP parameter space due to the generic overlapping divergences in the four-dimensional momentum space. By computing the so-called αβγ integrals arising from two-loop Feynman diagrams, we show how to deal with the divergences in the parameter space with the LORE method. By identifying the divergences in the UVDP parameter space to those in the subdiagrams, we arrive at the Bjorken–Drell analogy between Feynman diagrams and electrical circuits. The UVDP parameters are shown to correspond to the conductance or resistance in the electrical circuits, and the divergence in Feynman diagrams is ascribed to the infinite conductance or zero resistance. In particular, the sets of conditions required to eliminate the overlapping momentum integrals for obtaining the ILIs are found to be associated with the conservations of electric voltages, and the momentum conservations correspond to the conservations of electrical currents, which are known as the Kirchhoff laws in the electrical circuits analogy. As a practical application, we carry out a detailed calculation for one-loop and two-loop Feynman diagrams in the massive scalar ϕ4 theory, which enables us to obtain the well-known logarithmic running of the coupling constant and the consistent power-law running of the scalar mass at two-loop level. Especially, we present an explicit demonstration on the general procedure of applying the LORE method to the multiloop calculations of Feynman diagrams when merging with the advantage of Bjorken–Drell’s circuit analogy.

Large strong phases and CP violation in the annihilation processes B̄0→K+K-, K*±K∓, K*+K*-

The strong phases and CP violation in the rare B̄0→K+K-, K*±K∓, K*+K*- decays are investigated. As these decays proceed only via annihilation type diagrams in the standard model (SM), a dynamical gluon mass is introduced to avoid the infrared divergence in the soft endpoint regions. The Cutkosky rule is adopted to deal with a physical-region singularity of the on-mass-shell quark propagators, which leads to a big imaginary part and hence a large strong phase. As a consequence, large CP asymmetries are predicted in those decay modes due to a big interference between the annihilation amplitudes from penguin and tree operators, which may be tested in future more precise experiments.

Exploring final state hadron structure and SU(3) flavor symmetry breaking effects in D -> PP and D -> PV decays

Abstract.The non-leptonic two body decays

CP asymmetry in \(B \rightarrow \phi K_{S}\) in a general two-Higgs-doublet model with fourth-generation quarks

D\to PP

Lepton flavor-changing scalar interactions and g-2 of the muon

and

Searching for rephase-invariant CP- and CPT-violating observables in meson decays

D\to PV

Consistency of loop regularization method and divergence structure of QFTs Beyond one-loop order

are investigated based on the diagrammatic decomposition in a generalized factorization formalism. It is shown that to fit the experimental data, the SU(3) flavor symmetry breaking effects of the coefficients ais should be considered in

CP measurement in quantum teleportation of neutral mesons

D\to PP