Importance of Loop Effects in Explaining the Accumulated Evidence for New Physics in B Decays with a Vector Leptoquark

In recent years experiments revealed intriguing hints for new physics (NP) in B decays involving b -> c tau nu. and b -> sl(+)l(-) transitions at the 4 sigma and 5 sigma level, respectively. In addition, there are slight disagreements in b -> u tau nu and b -> d mu(+)mu(-) observables. While not significant on their own, they point in the same direction. Furthermore, V-us extracted from tau decays shows a slight tension (approximate to 2.5 sigma) with its value determined from Cabibbo-Kobayashi-Maskawa unitarity, and an analysis of BELLE data found an excess in B-d -> tau(+)tau(-). Concerning NP explanations, the vector leptoquark SU(2) singlet is of special interest since it is the only single particle extension of the standard model which can (in principle) address all the anomalies described above. For this purpose, large couplings to tau leptons are necessary and loop effects, which we calculate herein, become important. Including them in our phenomenological analysis, we find that neither the tension in V-us nor the excess in B-d -> tau(+)tau(-) can be fully explained without violating bounds from K -> pi nu(nu) over bar. However, one can account for b -> c tau nu and b -> u tau nu data finding intriguing correlations with B-q -> tau(+)tau(-) and K -> pi nu(nu) over bar. Furthermore, the explanation of b -> c tau nu predicts a positive shift in C-7 and a negative one in C-9, being nicely in agreement with the global fit to b -> sl(+)l(-) data. Finally, we point out that one can fully account for b -> c tau nu and b -> sl(+)l(-) without violating bounds from tau -> phi mu, gamma -> tau mu, or b -> s tau mu processes.