Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userDressing L_mu - L_tau in Color
476
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We consider a new massive vector-boson Z that couples to leptons through the L_mu - L_tau current, and to quarks through an arbitrary set of couplings. We show that such a model can be obtained from a renormalizable field theory involving new heavy fermions in an anomaly-free representation. The model is a candidate explanation for the discrepancy observed recently by the LHCb collaboration in angular distributions of the final state particles in the rare decay B to K* mu^+ mu^-. Interestingly, the new vector-boson contribution to the decay tau to mu nu_tau bar nu_mu can also remove a small tension in the measurement of the corresponding branching ratio. Constraints from light flavor meson-mixing restrict the coupling to the up- and down-quarks to be very small and thus direct production of the vector-boson at hadron colliders is strongly suppressed. The most promising ways to test the model is through the measurement of the Z decay to four leptons and through its effect on neutrino trident production of muon pairs. This latter process is a powerful but little-known constraint, which surprisingly rules out explanations of (g-2)_mu based on Z gauge bosons coupled to muon number, with mass of at least a few GeV.
rate research
Read More
In this paper, we study the phenomenology of a Dirac dark matter in the $L_mu-L_tau$ model and investigate the neutrino oscillation in the dark halo. Since dark matter couples to the muon neutrino and the tau neutrino with opposite sign couplings, it contributes effective potentials, $pm A_chi$, to the evolution equation of the neutrino flavor transition amplitude, which can be significant for high energy neutrino oscillations in a dense dark matter environment. We discuss neutrino masses, lepton mixing angles, Dirac CP phase, and neutrino oscillation probabilities in the dark halo using full numerical calculations. Results show that neutrinos can endure very different matter effects. When the potential $A_chi$ becomes ultra-large, three neutrino flavors decouple from each other.
As experimental null results increase the pressure on heavy weakly interacting massive particles (WIMPs) as an explanation of thermal dark matter (DM), it seems timely to explore previously overlooked regions of the WIMP parameter space. In this work we extend the minimal gauged $U(1)_{L_mu-L_tau}$ model studied in cite{Bauer:2018onh} by a light (MeV-scale) vector-like fermion $chi$. Taking into account constraints from cosmology, direct and indirect detection we find that the standard benchmark of $M_V=3 m_chi$ for DM coupled to a vector mediator is firmly ruled out for unit DM charges. However, exploring the near-resonance region $M_Vgtrsim 2 m_chi$ we find that this model can simultaneously explain the DM relic abundance $Omega h^2 =0.12$ and the $(g-2)_mu$ anomaly. Allowing for small charge hierarchies of $lesssimmathcal{O}(10)$, we identify a second window of parameter space in the few-GeV region, where $chi$ can account for the full DM relic density.
We consider right-handed neutrino dark matter $N_1$ in local $U(1)_{L_mu-L_tau}$-extended Ma model. With the light $U(1)_{mu-tau}$ gauge boson ($m_{Z} sim {cal O}(100)$ MeV) and small $U(1)_{mu-tau}$ gauge coupling ($g_{Z}sim 10^{-4}-10^{-3}$) which can accommodate the muon $(g-2)$ anomaly and is still allowed by other experimental constraints, we show that we can get correct relic density of dark matter for wide range of dark matter mass ($M_1 sim 10-100$ GeV), although the gauge coupling constant $g_{Z}$ is small. This is due to the fact that the annihilation cross section of dark matter pair is enhanced by $M_1^4/m_{Z}^4$ in the processes $N_1 N_1 to Z Z$ or $N_1 N_1 to Z H_2$. We also consider the constraints from direct detection, collider searches.
A recent proposal for explaining discrepancies in angular observables in the rare decay B --> K*mu+mu- with a gauged L_mu - L_tau current carried with it the prediction of lepton flavor universality violation in related B-meson decays. This prediction gained empirical support with a subsequent hint for lepton flavor universality violation in the B --> K l+l- decay by LHCb. In this short paper we fully quantify the prediction including the associated uncertainties. We also provide new predictions for a variety of additional observables sensitive to lepton flavor universality violation in B-meson decays.
We propose a local $U(1)_{L_mu-L_tau}$ model to explain $b to s mu^+ mu^-$ anomaly observed at the LHCb and Belle experiments. The model also has a natural dark matter candidate $N$. We introduce $SU(2)_L$-doublet colored scalar $widetilde{q}$ to mediate $b to s$ transition at one-loop level. The $U(1)_{L_mu-L_tau}$ gauge symmetry is broken spontaneously by the scalar $S$. All the new particles are charged under $U(1)_{L_mu-L_tau}$. We can obtain $C_9^{mu,{rm NP}} sim -1$ to solve the $b to smu^+mu^-$ anomaly and can explain the correct dark matter relic density of the universe, $Omega_{rm DM} h^2 approx 0.12$, simultaneously, while evading constraints from electroweak precision tests, neutrino trident experiments and other quark flavor-changing loop processes such as $b to s gamma$ and $B_s-overline{B}_s$ mixing. Our model can be tested by searching for $Z$ and new colored scalar at the LHC and $B to K^* u overline{ u}$ process at Belle-II.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
