Violation of Hund's rule in the lowest excited singlet-triplet pairs of dicyclohepta[cd,gh]pentalene and dicyclopenta[ef,kl]heptalene

Using the Pariser-Parr-Pople type MO method, the energy ordering of the lowest excited singlet-triplet pairs of the title molecules is examined by taking into account ample configuration interactions. In dicyclohepta[cd,gh]pentalene, it is shown that the lowest excited singlet state lies below the corresponding triplet state by about 6 kcal/mol. This violation of Hund's rule is ascribed entirely to the correlation effects brought about by spin polarization terms. Such a violation of Hund's rule is expected to occur in the lowest excited states of dicyclopenta[ef,kl]heptalene.     

叠加激发对相干态的非经典特性

从激发对相干态出发,构造了叠加激发对相干态,研究了该叠加态的非经典特性.结果表明:在一定条件下,随着相位的变化,叠加态场模的平均光子数呈现类似于拉比振荡的坍塌与复原现象,与激发对相干态相比,在叠加激发对相干态中亚泊松光子统计特性和CauchySchwatz不等式的破坏都得到了增强,但正交相位分量的压缩减弱.     

Radiatively induced flavour violation in the general two-Higgs doublet model with Yukawa alignment

The most general two-Higgs doublet model contains new sources of flavour violation that are usually in conflict with the experimental constraints. One possibility to suppress the exotic contribution to the flavour changing neutral currents consists on imposing the alignment of the Yukawa couplings. This condition presumably holds at a high-energy scale and is spoiled by the radiative corrections. We compute in this Letter the size of the radiatively induced flavour violating Higgs couplings at the electroweak scale. These also yield the absolute lower bound on the size of the exotic contributions to the flavour changing neutral currents in any two-Higgs doublet model, barring cancellations and the existence of discrete symmetries. We show that these contributions are well below the experimental bounds in large regions of the parameter space.     

Strong constraints on Lorentz violation using new γ-ray observations around PeV

The tiny modification of dispersion relation induced by Lorentz violation (LV) is an essential topic in quantum gravity (QG) theories, which can be magnified into significant effects when dealing with astrophysical observations at high energies and long propagation distances. LV would lead to photon decay at high energies; therefore, observations of high-energy photons could constrain LV or even QG theories. The Large High Altitude Air Shower Observatory (LHAASO) is the most sensitive gamma-array instrument currently operating above 100 TeV. Recently, LHAASO reported the detection of 12 sources above 100 TeV with maximum photon energy exceeding 1 PeV. According to these observations, the most stringent restriction is achieved in this study, i.e., limiting the LV energy scale to \begin{document}$1.7\times10^{33} $\end{document} eV, which is over 139,000 times that of the Planck energy, and achieving an improvement of approximately 1.9 orders of magnitude over previous limits.     

Search for a possible variation of the fine structure constant

The determination of the fine structure constant α and the search for its possible variation are considered. We focus on the role of the fine structure constant in modern physics and discuss precision tests of quantum electrodynamics.Different methods of a search for possible variations of fundamental constants are compared and those related to optical measurements are considered in detail.     

Different Routes to Lorentz Symmetry Violations

Recent observations of ultra high energy cosmic rays and gamma rays suggest that there are small violations of Lorentz symmetry. If there were no such violations, then the GZK cut off would hold and cosmic rays with energy ∼10²⁰ eV or higher would not be reaching the earth. However some such events seem to have been observed. This has lead to phenomenological models in which there is a small violation of the Lorentz symmetry or the velocity of light. However recent approaches which no longer consider a differentiable spacetime manifold already predict such violations. Similarly there are other theoretical reasons which also point to this. We briefly discuss some of these approaches and observe that Lorentz Symmetry violations can be tested by data from NASA’s GLAST satellite due for launch. Permanent address: International Institute for Applicable Mathematics & Information Sciences, Hyderabad, India & Udine, Italy. B.M. Birla Science Centre, Adarsh Nagar, Hyderabad 500 063, India.