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Using the Born-Oppenheimer approximation, we show that exotic resonances, X and Z, may emerge as QCD molecular objects made of colored two-quark lumps, states with heavy-light diquarks spatially separated from antidiquarks. With the same method we confirm that doubly heavy tetraquarks are stable against strong decays. Tetraquarks described here provide a new picture of exotic hadrons, as formed by the QCD analog of the hydrogen bond of molecular physics.
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In this paper we present in greater detail previous work on the Born-Oppenheimer approximation to treat the hydrogen bond of QCD, and add a similar treatment of doubly heavy baryons. Doubly heavy exotic resonances X and Z can be described as color molecules of two-quark lumps, the analogue of the H_2 molecule, and doubly heavy baryons as the analog of the H_2^+ ion, except that the two heavy quarks attract each other. We compare our results with constituent quark model and lattice QCD calculations and find further evidence in support of this upgraded picture of compact tetraquarks and baryons.
We theoretically investigate the quantum correlations (in terms of concurrence of indistinguishable electrons) in a prototype molecular system (hydrogen molecule). With the assistance of the standard approximations of the linear combination of atomic orbitals and the configuration interaction methods we describe the electronic wavefunction of the ground state of the H2 molecule. Moreover, we managed to find a rather simple analytic expression for the concurrence (the most used measure of quantum entanglement) of the two electrons when the molecule is in its lowest energy. We have found that concurrence does not really show any relation to the construction of the chemical bond.
As a cold dark matter candidate, the QCD axion may form Bose-Einstein condensates, called axion stars, with masses around $10^{-11},M_{odot}$. In this paper, we point out that a brand new astrophysical object, a Hydrogen Axion Star (HAS), may well be formed by ordinary baryonic matter becoming gravitationally bound to an axion star. We study the properties of the HAS and find that the hydrogen cloud has a high pressure and temperature in the center and is likely in the liquid metallic hydrogen state. Because of the high particle number densities for both the axion star and the hydrogen cloud, the feeble interaction between axion and hydrogen can still generate enough internal power, around $10^{13}~mbox{W}times(m_a/5~mbox{meV})^4$, to make these objects luminous point sources. High resolution ultraviolet, optical and infrared telescopes can discover HAS via black-body radiation.
We present a variational MonteCarlo (VMC) and lattice regularized diffusion MonteCarlo (LRDMC) study of the binding energy and dispersion curve of the water dimer. As a variation ansatz we use the JAGP wave function, an implementation of the resonating valence bond (RVB) idea. Actually one the aim of the present work is to investigate how the bonding of two water molecules, as a prototype of the hydrogen-bonded complexes, could be described within an JAGP approach. Using a pseudopotential for the inert core of the Oxygen, with a full optimization of the variational parameters, we obtain at the VMC level a binding energy of -4.5(0.1) Kcal/mol, while LRDMC calculations gives -4.9(0.1) Kcal/mol (experiment 5 Kcal/Mol). The calculated dispersion curve reproduces both at the VMC and LRDMC level the miminum position and the curvature.The quality of the WF gives us the possibility to dissect the binding energy in different contributions by appropriately switching off determinantal and Jastrow terms in the JAGP: we estimate the dynamical contribution to the binding energy to be of the order of 1.4(0.2) Kcal/Mol whereas the covalent contribution about 1.0(0.2) Kcal/Mol. JAGP reveales thus a promising WF for describing systems where both dispersive and covalent forces play an important role.
The glass transition in hydrogen-bonded glass formers differs from the glass transition in other glass formers. The Eshelby rearrangements of the highly viscous flow are superimposed by strongly asymmetric hydrogen bond rupture processes, responsible for the excess wing. Their influence on the shear relaxation spectrum is strong in glycerol and close to zero in PPE, reflecting the strength of the hydrogen bond contribution to the high frequency shear modulus. An appropriate modification of a recent theory of the highly viscous flow enables a quantitative common description of the relaxation spectra in shear, linear and non-linear dielectrics, and heat capacity.
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