Addressing the CKM unitarity problem with a vector-like up quark

We point out that hints of deviations from unitarity in the first row of the CKM matrix may be explained by the presence of a single vector-like top. We study how the stringent experimental constraints arising from CP Violation in the kaon sector and from meson mixing such as $$ {D}^0\hbox{-} {\overline{D}}^0,{K}^0\hbox{-} {\overline{K}}^0 $$ D 0 ‐ D ¯ 0 , K 0 ‐ K ¯ 0 and $$ {B}_{d,s}^0\hbox{-} {\overline{B}}_{d,s}^0 $$ B d , s 0 ‐ B ¯ d , s 0 can be satisfied in the proposed framework. In order for the deviations from unitarity to be of the required size while keeping the theory perturbative, the new top quark should have a mass mT ≲ 7 TeV which could be probed in upcoming experiments at the energy frontier.

Investigating the Atomki anomaly in the framework of axial (ABJ) anomaly

An anomaly observed in the 8Be nuclear transition by the Atomki collaboration hints at a light, neutral boson decaying into an [Formula: see text] pair with a mass of about 17 MeV. In this paper, we study the Atomki anomaly in the framework of axial (ABJ) anomaly. Some theoretical results indicate that the X17 particle is the color singlet pseudoscalar. We take the X17 particle as a pseudoscalar meson [Formula: see text] system which has the axial (ABJ) anomaly, where [Formula: see text] denotes the up quark. Besides this, we also give an interpretation for E38 particle with a mass of about 38 MeV as a pseudoscalar meson [Formula: see text] system. We obtain the correct masses of the two pseudoscalars by a non-perturbative mass formula.

Completing 1/$$ {m}_b^3 $$ corrections to non-leptonic bottom-to-up-quark decays

We compute the contributions of dimension six two-quark operators to the non-leptonic decay width of heavy hadrons due to the flavor changing bottom-to-up-quark transition in the heavy quark expansion. Analytical expressions for the Darwin term ρD and the spin-orbit term ρLS are obtained with leading order accuracy.

Strong CP Violation Tamed in The Presence of Gravity

In a multi-fold universe, gravity emerges from entanglement through the multi-fold mechanisms. As a result, gravity-like effects appear in between entangled particles that they be real or virtual. Long range, massless gravity results from entanglement of massless virtual particles. Entanglement of massive virtual particles leads to massive gravity contributions at very smalls scales. Multi-folds mechanisms also result into a spacetime that is discrete, with a random walk fractal structure and non-commutative geometry that is Lorentz invariant and where spacetime nodes and particles can be modeled with microscopic black holes. All these recover General relativity at large scales and semi-classical model remain valid till smaller scale than usually expected. Gravity can therefore be added to the Standard Model. This can contribute to resolving several open issues with the Standard Model. The strong CP violation problem is one of these issues: QCD predicts CP violation, yet no CP violation has ever been observed involving the strong interaction (when it occurs, it is for the weak interaction). In this paper we show that when adding gravity to the Standard Model, in a multi-fold universe, gravity allows the mass of the up quark to be smaller (close to, or equal to zero). This symmetry, or quasi symmetry, is a way to eliminate the CP violation contributions in QCD, therefore resolving the problem. It argues for evolving the Standard Model to add gravity, if non negligible at very small scales. No New Physics are introduced as new particles, which could also explain why axions have never been observed, and we may have to remove them as candidates to explain dark matter.

An approach to the instanton effect in B system

We discuss the constraint on the size of QCD instanton effects in low-energy effective theory. Among various instanton effects in meson mass spectrum and dynamics, we concentrate on the instanton-induced masses of light quarks. The famous instanton-induced six-quark interaction, so-called ’t Hooft vertex, could give nonperturbative quantum corrections to light quark masses. Many works have already been achieved to constrain the mass corrections in light meson system, or the system of [Formula: see text], [Formula: see text], [Formula: see text] and [Formula: see text], and now we know for a fact that the instanton-induced mass of up-quark is too small to realize the solution of the strong CP problem by vanishing current mass of up-quark. In this work, we give a constraint on the instanton-induced mass correction to light quarks from the mass spectrum of heavy mesons, [Formula: see text], [Formula: see text], [Formula: see text] and their antiparticles. To accomplish this, the complete second-order chiral symmetry breaking terms are identified in heavy meson effective theory. We find that the strength of the constraint from heavy meson masses is at the same level of that from light mesons, and it would be made even stronger by more precise data from future [Formula: see text] factories and lattice calculations.

Topological susceptibility with a single light quark flavour

One of the historical suggestions to tackle the strong CP problem is to take the up quark mass to zero while keeping md finite. The θ angle is then supposed to become irrelevant, i.e. the topological susceptibility vanishes. However, the definition of the quark mass is scheme-dependent and identifying the mu = 0 point is not trivial, in particular with Wilson-like fermions. More specifically, up to our knowledge there is no theoretical argument guaranteeing that the topological susceptibility exactly vanishes when the PCAC mass does. We will present our recent progresses on the empirical check of this property using Nf = 1 + 2 flavours of clover fermions, where the lightest fermion is tuned very close to [see formula in PDF] and the mass of the other two is kept of the order of magnitude of the physical ms. This choice is indeed expected to amplify any unknown non-perturbative effect caused by mu ≠ md. The simulation is repeated for several βs and those results, although preliminary, give a hint about what happens in the continuum limit.

Studying the lepton number and lepton flavor violating $D^0\to e^\pm\mu^\mp$ and $D^+_{d/s}\to \pi(K)^+e^\pm\mu^\mp$ decays

The rare D decays are sensitive to new physics involving the up quark sector such as certain R-parity violating supersymmetric models. We study the lepton number and lepton flavor violating [Formula: see text] and [Formula: see text] decays in the supersymmetry without R-parity. From the best experimental upper limits of these decay branching ratios, we derive constraints on the relevant coupling products for the first time, and examine their contributions to relevant branching ratios and dileptonic invariant mass spectra. We find that all branching ratios are very sensitive to moduli of the squark exchange coupling products. Accurate measurements of these decay branching ratios in the future experiments at LHC and BESIII could give very strong bounds on relevant lepton number and lepton flavor violating coupling products.