Abstract
The Nelson-Barr mechanism to solve the strong CP problem requires vector- like quarks (VLQs) to transmit the spontaneous CP breaking to the SM. We study the scenario where only these VLQs are within reach at the TeV scale while the spontaneous CP breaking sector is inaccessible. We investigate how these VLQs of Nelson-Barr type differ from generic VLQs and find from parameter counting that one less parameter is needed. In particular, for one VLQ of Nelson-Barr type, there is only one CP odd quantity that is responsible for all CP violation. In this case, we solve the technical problem of parametrizing only the new physics parameters while keeping the SM parameters as independent inputs. For one down-type VLQ, the model is largely flavor safe because the VLQ couplings to the SM up quarks and the W are hierarchically smaller for lighter quarks.
Highlights
Potential and is dynamically driven to zero in the potential minimum [2, 3]; (ii) CP is a fundamental symmetry and its violation manifests itself only through spontaneous breaking at lower energies making θcalculable and to arise only at loop level, potentially justifying its tiny value [4,5,6,7,8,9,10]
We study the scenario where only these vectorlike quarks (VLQs) are within reach at the TeV scale while the spontaneous CP breaking sector is inaccessible
We have defined and analyzed the SM augmented by vector-like quarks of Nelson-Barr type (NB-VLQs)
Summary
To define what we mean by VLQs of Nelson-Barr type (NB-VLQs), we start by describing generic VLQs. We consider only the case of singlets of SU(2)L of charge −1/3 denoted by BrL, BrR, r = 1, . In Nelson-Barr type models CP is a fundamental symmetry ( real parameters) which is only spontaneously broken ( complex M Bd) at a scale much higher than the VLQ masses [4, 5]. Considering that the effective mass matrix arising from (2.4) has real determinant, the strong CP parameter θvanishes at tree level and the problem is solved if the loop corrections are small enough. We can see NB-VLQs comprise only a subclass of general VLQs by counting the number of physical parameters in the Lagrangian (2.4):. One of our main goals is to seek ways to distinguish generic VLQs from NB-VLQs
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