Two-loop electroweak corrections to the Top-Quark Contribution to ϵK

The parameter ϵK measures CP violation in the neutral kaon system. It is a sensitive probe of new physics and plays a prominent role in the global fit of the Cabibbo-Kobabyashi-Maskawa matrix. The perturbative theory uncertainty is currently dominated by the top-quark contribution. Here, we present the calculation of the full two-loop electroweak corrections to the top-quark contribution to ϵK, including the resummation of QED-QCD logarithms. We discuss different renormalization prescriptions for the electroweak input parameters. In the traditional normalization of the weak Hamiltonian with two powers of the Fermi constant GF, the top-quark contribution is shifted by −1%.

Testing CPT Symmetry with Neutral K Mesons: A Review

The neutral kaon system is a very peculiar system that offers unique possibilities to perform precise tests of the CPT symmetry. The entanglement of neutral kaon pairs that are produced at a ϕ-factory opens up new ways and scenarios in order to test this fundamental discrete symmetry. In this paper, the results of the most recent and significant CPT tests are reviewed. Experiments have set stringent limits on the CPT-violating parameters of different phenomenological models, some of them associated to possible decoherence mechanisms or Lorentz symmetry violation which might be justified in a quantum gravity framework. The present results show no violation of CPT symmetry, while their accuracy in some cases reaches the interesting level at which–in the most optimistic scenarios–quantum gravity effects might show up.

Kaon decays shedding light on massless dark photons

We explore kaon decays with missing energy carried away by a massless dark photon, $${{\overline{\gamma }}}$$ γ ¯ , assumed to have flavor-changing dipole-type couplings to the d and s quarks. We consider in particular the neutral-kaon modes $$K_L\rightarrow \gamma {{\overline{\gamma }}}$$ K L → γ γ ¯ and $$K_L\rightarrow \pi ^0\gamma {{\overline{\gamma }}}$$ K L → π 0 γ γ ¯ and their $$K_S$$ K S counterparts, as well as the charged-kaon channel $$K^+\rightarrow \pi ^+\gamma {{\overline{\gamma }}}$$ K + → π + γ γ ¯ , each of which also has an ordinary photon, $$\gamma $$ γ , in the final state. In addition, we look at $$K_{L,S}\rightarrow \pi ^+\pi ^-{{\overline{\gamma }}}$$ K L , S → π + π - γ ¯ and $$K^+\rightarrow \pi ^+\pi ^0{{\overline{\gamma }}}$$ K + → π + π 0 γ ¯ . Interestingly, the same $$ds{{\overline{\gamma }}}$$ d s γ ¯ interactions give rise to the flavor-changing two-body decays of hyperons with missing energy and are subject to model-independent constraints that can be inferred from the existing hyperon data. Taking this into account, we obtain branching fractions $${{{\mathcal {B}}}}(K_L\rightarrow \gamma {{\overline{\gamma }}})$$ B ( K L → γ γ ¯ ) and $$\mathcal{B}(K_L\rightarrow \pi ^0\gamma {{\overline{\gamma }}})$$ B ( K L → π 0 γ γ ¯ ) which can be as high as $$10^{-3}$$ 10 - 3 and $$10^{-6}$$ 10 - 6 , respectively, one or both of which may be within the sensitivity reach of the KOTO experiment. Furthermore, we find that $${{{\mathcal {B}}}}(K^+\rightarrow \pi ^+\gamma {{\overline{\gamma }}})$$ B ( K + → π + γ γ ¯ ) and $$\mathcal{B}(K^+\rightarrow \pi ^+\pi ^0{{\overline{\gamma }}})$$ B ( K + → π + π 0 γ ¯ ) are allowed to be maximally of order $$10^{-6}$$ 10 - 6 as well, which may be probed by NA62. Complementarily, the hyperon modes can have rates which are potentially accessible by BESIII. Thus, these ongoing experiments could soon be able to offer significant tests on the existence of the massless dark photon.

Experimental study of the $ \gamma p \rightarrow K^{0}\Sigma^{+}$, $ \gamma n \rightarrow K^{0} \Lambda$, and $ \gamma n \rightarrow K^{0} \Sigma^{0}$ reactions at the Mainz Microtron

This work measured $ \mathrm{d}\sigma/\mathrm{d}\Omega$dσ/dΩ for neutral kaon photoproduction reactions from threshold up to a c.m. energy of 1855MeV, focussing specifically on the $ \gamma p\rightarrow K^0\Sigma^+$γp→K0Σ+, $ \gamma n\rightarrow K^0\Lambda$γn→K0Λ, and $ \gamma n\rightarrow K^0 \Sigma^0$γn→K0Σ0 reactions. Our results for $ \gamma n\rightarrow K^0 \Sigma^0$γn→K0Σ0 are the first-ever measurements for that reaction. These data will provide insight into the properties of $ N^{\ast}$N* resonances and, in particular, will lead to an improved knowledge about those states that couple only weakly to the $ \pi N$πN channel. Integrated cross sections were extracted by fitting the differential cross sections for each reaction as a series of Legendre polynomials and our results are compared with prior experimental results and theoretical predictions.

Absolute Hidden Symmetry in Time and Absolute Asymmetry in Mass and Velocity between a Particle and Its Anti-Particle

In this paper we will the discuss possible hidden symmetry in time and the possible asymmetry in mass and velocity between a particle and its anti-particle. Possible hidden symmetry in time between a particle and its anti-particle manifested in their corresponding possible hidden variables in time, fr and -fr  was first discussed in Brodet (2017b). In this paper we will extend the discussion and discuss how the above possible hidden symmetry in time and its corresponding possible symmetry in absolute position, energy and momentum, may yield an asymmetry in mass and velocity of a particle and its corresponding anti-particle. We will deconstruct the particle’s and anti-particle’s absolute position, into three complex number describing the particle/anti-particle time, velocity and mass. The particle/anti-particle symmetry and asymmetry of the above complex numbers will be discussed in the context of parity violation and the known asymmetry in angular production of particles and anti-particles. Moreover, the possible mass asymmetry will be used to explain the CP violation in the neutral kaon system. Finally, experimental ways to investigate and test the above are presented.