Flavor-changing neutral currents and seesaw masses for quarks

Anjan S. Joshipura

doi:10.1103/PhysRevD.39.878

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Flavor-changing neutral currents and seesaw masses for quarks

Anjan S. Joshipura

The Institute of Mathematical Sciences, Madras 600113, India

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Phys. Rev. D 39, 878 – Published 1 February, 1989

DOI: https://doi.org/10.1103/PhysRevD.39.878

Abstract

The structure of flavor-changing neutral currents (FCNC’s) which arise when one tries to give masses to quarks through the analogue of the seesaw mechanism for neutrino masses is studied. General conditions for the absence of FCNC’s in the seesaw limit are derived. A specific model where these conditions are satisfied by the tree-level-quark mass matrices is identified. The FCNC’s get generated in this model through radiative corrections to quark masses. These corrections lead to a hierarchy $F_{12}$ < $F_{13}$ < $F_{23}$ in typical strength $F_{ij}$ of the neutral-current transition between ith and jth generations. Moreover the flavor-changing transitions between down quarks are suppressed compared to the corresponding transitions between up quarks. As a consequence, the FCNC’s connecting d to s quark are greatly suppressed in conformity with observations such as $K^{0}$ -K $¯^{0}$ mixing and the decay $K_{L}$ → $μ^{+}$ $μ^{-}$ . In contrast, the transitions between c and t quarks could have observable magnitudes. The branching ratio for Z→t¯c could be as large as $10^{- 6}$ – $10^{- 7}$ in the model considered here. The $D^{0}$ -D $¯^{0}$ mixing could also be in the vicinity of the present experimental limits.

References (21)

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D. Chang and R. N. Mohapatra, Phys. Rev. Lett. 58, 1600 (1987).
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Note that because of the assumed equality of Yukawa couplings in the u and d sectors the states | $φ_{i}$ > are eigenfunctions also of $M_{d}$ at the tree level.
We should remember here that this is true for ( $F_{L, R}$ $)_{13}$ only under the simplifying assumption of neglecting $a_{2, 31}$ and $b_{2, 2}$ in Eqs. (4.3). But the basic fact that ( $F_{L, R}$ $)_{13}$ involves parameters of the same order as $V_{ub}$ is independent of this.
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It has been observed by many authors that a large $B_{d}^{0}$ -B ${bar}_{d}^{0}$ mixing generally requires a heavy top quark. See G. Altarelli, in Proceedings of the European Physical Society High Energy Physics Conference [International Europhysics Conference on High Energy Physics (Ref. 18), p. 1002, for original references. However, a light top quark cannot be ruled out by $B_{d}^{0}$ -B ${bar}_{d}^{0}$ mixing alone, see, e.g., J. R. Cudell et al., Phys. Lett. B 196, 227 (1987).
K. S. Babu et al., Phys. Lett. B 205, 540 (1988).

[c1] M. Gell-Mann, P. Ramond, and R. Slansky, in Supergravity, proceedings of the Stony Brook Workshop, edited by P. van Nieuwenhuizen and D. Z. Freedman (North-Holland, New York, 1979); T. Yanagida, in Proceedings of the Workshop on the Baryon Number of the Universe and Unified Theories, Tsukuba, Japan, 1979, edited by O. Sawada and A. Sugamoto (KEK, Tsukuba, 1979).

[c2] D. Chang and R. N. Mohapatra, Phys. Rev. Lett. 58, 1600 (1987).

[c3] A. Davidson and K. C. Wali, Phys. Rev. Lett. 59, 393 (1987); ibid. 60, 1813 (1988).

[c4] S. Rajpoot, Phys. Lett. B 191, 122 (1987); Phys. Rev. D 36, 1479 (1987) Phys. Rev. Lett. 60, 2003 (1988).

[c5] F. del Augila, G. L. Kane and M. Quiros, Phys. Lett. B 196, 531 (1987).

[c6] R. N. Mohapatra, Phys. Lett. B 198, 69 (1987); ibid. 201, 517 (1988).

[c7] B. S. Balakrishna, Phys. Rev. Lett. 60, 1602 (1988).

[c8] B. S. Balakrishna, A. L. Kagan and R. N. Mohapatra, Phys. Lett. B 205, 345 (1988).

[c9] S. Glashow, J. Iliopoulos and L. Maiani, Phys. Rev. D 2, 1285 (1970).

[c10] J. C. Pati and A. Salam, Phys. Rev. D 10, 275 (1974); R. N. Mohapatra and J. C. Pati, ibid. 11, 566 (1975); R. N. Mohapatra and G. Senjanović, ibid. 12, 1502 (1975); Phys. Rev. Lett. 44, 912 (1980) Phys. Rev. D 23, 165 (1981).

[c11] J. K. Bajaj and G. Rajasekaran, Phys. Lett. 93B, 461 (1980); Pramana 12, 397 (1979) V. Barger, E. Ma and K. Whisnant, Phys. Rev. D 26, 2378 (1982).

[c12] Note that because of the assumed equality of Yukawa couplings in the u and d sectors the states | $φ_{i}$ > are eigenfunctions also of $M_{d}$ at the tree level.

[c13] We should remember here that this is true for ( $F_{L, R}$ $)_{13}$ only under the simplifying assumption of neglecting $a_{2, 31}$ and $b_{2, 2}$ in Eqs. (4.3). But the basic fact that ( $F_{L, R}$ $)_{13}$ involves parameters of the same order as $V_{ub}$ is independent of this.

[c14] M. Clements et al., Phys. Rev. D 27, 570 (1983); V. Ganapathi et al., ibid. 27, 579 (1983); A. Axelrod, Nucl. Phys. B209, 349 (1982).

[c15] B. Mukhopadhyaya and A. Raychaudhuri, University of Calcutta Report No.CUPP-88/2 (unpublished); M. J. Duncan, Phys. Rev. D 31, 1139 (1985).

[c16] B. McWilliams and O. Shankar, Phys. Rev. D 22, 2853 (1980).

[c17] A. Datta and D. Kumbhakar, Z. Phys. C 27, 515 (1985); A. Datta and K. Niyogi, Phys. Rev. D 20, 2441 (1979).

[c18] A. Seiden, in Proceedings of the European Physical Society High Energy Physics Conference [International Europhysics Conference on High Energy Physics], Uppsala, Sweden, 1987, edited by O. Botner (European Physical Society, Geneva, Switzerland, 1987), p. 368.

[c19] P. Haas et al., Phys. Rev. Lett. 60, 1614 (1988).

[c20] It has been observed by many authors that a large $B_{d}^{0}$ -B ${bar}_{d}^{0}$ mixing generally requires a heavy top quark. See G. Altarelli, in Proceedings of the European Physical Society High Energy Physics Conference [International Europhysics Conference on High Energy Physics (Ref. 18), p. 1002, for original references. However, a light top quark cannot be ruled out by $B_{d}^{0}$ -B ${bar}_{d}^{0}$ mixing alone, see, e.g., J. R. Cudell et al., Phys. Lett. B 196, 227 (1987).

[c21] K. S. Babu et al., Phys. Lett. B 205, 540 (1988).

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Flavor-changing neutral currents and seesaw masses for quarks

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