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Register a new userNonuniversal Gaugino Masses and Muon g-2
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We consider two classes of supersymmetric models with nonuniversal gaugino masses at M_GUT in an attempt to resolve the apparent muon g-2 anomaly encountered in the Standard Model. We explore two distinct scenarios, one in which all gaugino masses have the same sign at M_GUT, and a second case with opposite sign gaugino masses. The sfermion masses in both cases are assumed to be universal at M_GUT. We exploit the non universality among gaugino masses to realize large mass splitting between the colored and non-colored sfermions. Thus, the sleptons can have masses in the few hundred GeV range, whereas the colored sparticles turn out to be an order of magnitude or so heavier. In both models the resolution of the muon g-2 anomaly is compatible, among other things, with a 125-126 GeV Higgs boson mass and the WMAP dark matter bounds.
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In unified $mathcal{N}=1$ supergravity scenario the gaugino masses can be non-universal. The patterns of these non-universalities are dictated by the vacuum expectation values of non-singlet chiral super-fields in visible sector. Here, we have analysed the model independent correlations among the gaugino masses with an aim to explain the $[1div 3]sigma$ excess of muon (g-2) ($Delta a_mu$). We have also encapsulated the interconnections among other low and high scale parameters, compatible with the collider constraints, Higgs mass, relic density and flavour data. We have noted that the existing non-universal models are not capable enough to explain $Delta a_mu$ at $[1div 2]sigma$ level. In the process, we have also shown the impact of recent limits from the searches for disappearing track and long lived charged particles at the LHC. These are the most stringent limits so far ruling out a large parameter space allowed by other constraints. We have also performed model guided analysis where gaugino masses are linear combination of contributions coming from singlet and non-singlet chiral super-fields. Here, a new mixing parameter has been introduced. Following the earlier methodology, we have been able to constrain this mixing parameter and pin down the promising models on this notion.
We argue that in order to account for the muon anomalous magnetic moment $g-2$, dark matter and LHC data, non-universal gaugino masses $M_i$ at the high scale are required in the framework of the Minimal Supersymmetric Standard Model (MSSM). We also need a right-handed smuon $tildemu_R$ with a mass around 100 GeV, evading LHC searches due to the proximity of a neutralino $tilde{chi}^0_1$ several GeV lighter which allows successful dark matter. We discuss such a scenario in the framework of an $SU(5)$ Grand Unified Theory (GUT) combined with $A_4$ family symmetry, where the three $overline{5}$ representations form a single triplet of $A_4$ with a unified soft mass $m_F$, while the three $10$ representations are singlets of $A_4$ with independent soft masses $m_{T1}, m_{T2}, m_{T3}$. Although $m_{T2}$ (and hence $tildemu_R$) may be light, the muon $g-2$ and relic density also requires light $M_1simeq 250$ GeV, which is incompatible with universal gaugino masses due to LHC constraints on $M_2$ and $M_3$ arising from gaugino searches. After showing that universal gaugino masses $M_{1/2}$ at the GUT scale are excluded by gluino searches, we provide a series of benchmarks which show that while $M_{1}= M_{2} ll M_3$ is also excluded by chargino searches, $M_{1}< M_{2} ll M_3$ is currently allowed. Even this scenario is almost excluded by the tension between the muon $g-2$, relic density, Dark Matter direct detection and LHC data. The surviving parameter space is characterised by a higgsino mass $mu approx -300$ GeV, as required by the muon $g-2$. The LHC will be able to fully test this scenario with the upgraded luminosity via muon-dominated tri- and di-lepton signatures resulting from higgsino dominated $tilde{chi}^pm_1 , tilde{chi}^0_2$ and $tilde{chi}^+_1 , tilde{chi}^-_1$ production.
The stringent experimental bound on $mu rightarrow e gamma$ is compatible with a simultaneous and sizable new physics contribution to the electron and muon anomalous magnetic moments $(g-2)_ell$ ($ell=e,,mu$), only if we assume a non-trivial flavor structure of the dipole operator coefficients. We propose a mechanism in which the realization of the $(g-2)_ell$ correction is manifestly related to the mass generation through a flavor symmetry. A radiative flavon correction to the fermion mass gives a contribution to the anomalous magnetic moment. In this framework, we introduce a chiral enhancement from a non-trivial $mathcal{O}(1)$ quartic coupling of the scalar potential. We show that the muon and electron anomalies can be simultaneously explained in a vast region of the parameter space with predicted vector-like mediators of masses as large as $M_chiin [0.6,2.5]$~TeV.
We present a model of radiative neutrino masses which also resolves anomalies reported in $B$-meson decays, $R_{D^{(star)}}$ and $R_{K^{(star)}}$, as well as in muon $g-2$ measurement, $Delta a_mu$. Neutrino masses arise in the model through loop diagrams involving TeV-scale leptoquark (LQ) scalars $R_2$ and $S_3$. Fits to neutrino oscillation parameters are obtained satisfying all flavor constraints which also explain the anomalies in $R_{D^{(star)}}$, $R_{K^{(star)}}$ and $Delta a_mu$ within $1, sigma$. An isospin-3/2 Higgs quadruplet plays a crucial role in generating neutrino masses; we point out that the doubly-charged scalar contained therein can be produced in the decays of the $S_3$ LQ, which enhances its reach to 1.1 (6.2) TeV at $sqrt s=14$ TeV high-luminosity LHC ($sqrt s=100$ TeV FCC-hh). We also present flavor-dependent upper limits on the Yukawa couplings of the LQs to the first two family fermions, arising from non-resonant dilepton ($pp rightarrow ell^+ ell^-$) processes mediated by $t$-channel LQ exchange, which for 1 TeV LQ mass, are found to be in the range $(0.15 - 0.36)$. These limits preclude any explanation of $R_{D^{(star)}}$ through LQ-mediated $B$-meson decays involving $ u_e$ or $ u_mu$ in the final state. We also find that the same Yukawa couplings responsible for the chirally-enhanced contribution to $Delta a_mu$ give rise to new contributions to the SM Higgs decays to muon and tau pairs, with the modifications to the corresponding branching ratios being at (2-6)% level, which could be tested at future hadron colliders, such as HL-LHC and FCC-hh.
We propose a leptoquark model with two scalar leptoquarks $S^{}_1 left( bar{3},1,frac{1}{3} right)$ and $widetilde{R}^{}_2 left(3,2,frac{1}{6} right)$ to give a combined explanation of neutrino masses, lepton flavor mixing and the anomaly of muon $g-2$, satisfying the constraints from the radiative decays of charged leptons. The neutrino masses are generated via one-loop corrections resulting from a mixing between $S^{}_1$ and $widetilde{R}^{}_2$. With a set of specific textures for the leptoquark Yukawa coupling matrices, the neutrino mass matrix possesses an approximate $mu$-$tau$ reflection symmetry with $left( M^{}_ u right)^{}_{ee} = 0$ only in favor of the normal neutrino mass ordering. We show that this model can successfully explain the anomaly of muon $g-2$ and current experimental neutrino oscillation data under the constraints from the radiative decays of charged leptons.
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