B-anomalies from flavorful U(1)$$'$$ extensions, safely

Abstract

Abstract$$U(1)^\prime $$ U ( 1 ) ′ extensions of the standard model with generation-dependent couplings to quarks and leptons are investigated as an explanation of anomalies in rare B-decays, with an emphasis on stability and predictivity up to the Planck scale. To these ends, we introduce three generations of vector-like standard model singlet fermions, an enlarged, flavorful scalar sector, and, possibly, right-handed neutrinos, all suitably charged under the $$U(1)^\prime $$ U ( 1 ) ′ gauge interaction. We identify several gauge-anomaly free benchmarks consistent with $$B_s$$ B s -mixing constraints, with hints for electron-muon universality violation, and the global $$b \rightarrow s$$ b → s fit. We further investigate the complete two-loop running of gauge, Yukawa and quartic couplings up to the Planck scale to constrain low-energy parameters and enhance the predictive power. A characteristic of models is that the $$Z^\prime $$ Z ′ with TeV-ish mass predominantly decays to invisibles, i.e. new fermions or neutrinos. $$Z^\prime $$ Z ′ -production can be studied at a future muon collider. While benchmarks feature predominantly left-handed couplings $$C_9^{\mu }$$ C 9 μ and $$C_{10}^{\mu }$$ C 10 μ , right-handed ones can be accommodated as well.

Asymptotic safety guaranteed for strongly coupled gauge theories

“…We emphasize that the boundary at P min in (18) is not part of the conformal window. The reason for this is that whenever P → P min the inequality in (10) becomes an equality, meaning that β 2 → 0 non-perturbatively at the fixed point (8).…”

“…Templates with strict perturbative control have been found for unitary [5], orthogonal and symplectic [9], or product gauge groups [10], and supersymmetry [11]. This has also triggered new ideas for model building [12,13], asymptotically safe extensions of the Standard Model explaining the electron and muon g − 2 anomalies [14][15][16] whose new type of flavor phenomenology can be tested at colliders [17], and explanations of flavour anomalies as evidenced in rare B-meson decays [18]. Further results cover vacuum stability [19] including the Higgs [14][15][16]18], abelian factors [13], global fixed points [20], aspects of radiative symmetry breaking [21], UV conformal windows [22], and fixed point mergers [23].…”

“…Moreover, it is well known that weakly coupled fixed points often require a large number of gauge and matter fields, such as in a Veneziano large-N limit, while decreasing the number of matter fields turns fixed point interactions stronger. In the context of asymptotically safe model building where only finitely many new matter fields are added to the Standard Model [12][13][14][15][16][17][18], it becomes paramount to control the size of UV conformal windows non-perturbatively, and to understand how few matter fields can sustain an underlying fixed point [22,23]. It would be equally important to understand whether or not qualitatively new types of fixed points arise at strong coupling, beyond those discovered at weak coupling.…”

Flavour alignment of New Physics in light of the (g − 2)μ anomaly

“…Extensions of the SM aiming at combined explanations of a µ and (some of) the B physics anomalies have been presented in refs. [29][30][31][32][33][34][35][36][37][38][39][40], The a µ anomaly involves only leptons of the second generation and, taken alone, does not indicate any violation of flavour quantum numbers. It also does not provide a clear indication on the energy scale of the associated new dynamics [16,17].…”

Interpreting B-anomalies within an extended 331 gauge theory

“…Within the SM this cannot be achieved as the theory is sequential, so that the e − and µ − carry the same gauge charges. One possible way out is to postulate a new U (1) X gauge symmetry under which e − and µ − carry different charges [13][14][15][16][17].…”