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The lightest hybrid meson supermultiplet in QCD
We interpret the spectrum of meson states recently obtained in nonperturbative lattice QCD calculations in terms of constituent quark-antiquark bound states and states, called ''hybrids'', in which the qq pair is supplemented by an excitation of the gluonic field. We identify a lightest supermultiplet of hybrid mesons with J{sup PC}=(0,1,2){sup -+},1{sup --} built from a gluonic excitation of chromomagnetic character coupled to qq in an S-wave. The next lightest hybrids are suggested to be quark orbital excitations with the same gluonic excitation, while the next distinct gluonic excitation is significantly heavier. Existing models of gluonic excitations are compared to these findings and possible phenomenological consequences explored.
Higgs potential in the type II seesaw model
The standard model Higgs sector, extended by one weak gauge triplet of scalar fields with a very small vacuum expectation value, is a very promising setting to account for neutrino masses through the so-called type II seesaw mechanism. In this paper we consider the general renormalizable doublet/triplet Higgs potential of this model. We perform a detailed study of its main dynamical features that depend on five dimensionless couplings and two mass parameters after spontaneous symmetry breaking, and highlight the implications for the Higgs phenomenology. In particular, we determine (i) the complete set of tree-level unitarity constraints on the couplings of the potential and (ii) the exact tree-level boundedness from below constraints on these couplings, valid for all directions. When combined, these constraints delineate precisely the theoretically allowed parameter space domain within our perturbative approximation. Among the seven physical Higgs states of this model, the mass of the lighter (heavier) CP{sub even} state h{sup 0} (H{sup 0}) will always satisfy a theoretical upper (lower) bound that is reached for a critical value {mu}{sub c} of {mu} (the mass parameter controlling triple couplings among the doublet/triplet Higgses). Saturating the unitarity bounds, we find an upper bound m{sub h}{sup 0}<O(0.7-1 TeV), while the upper bound for the remaining Higgses lies in the range of several tens of TeV. However, the actual masses can be much lighter. We identify two regimes corresponding to {mu} > or approx. {mu}{sub c} and {mu} < or approx. {mu}{sub c}. In the first regime the Higgs sector is typically very heavy, and only h{sup 0} that becomes SM-like could be accessible to the LHC. In contrast, in the second regime, somewhat overlooked in the literature, most of the Higgs sector is light. In particular, the heaviest state H{sup 0} becomes SM-like, the lighter states being the CP{sub odd} Higgs, the (doubly) charged Higgses, and a decoupled h{sup 0}, possibly leading to a distinctive phenomenology at the colliders.
Minimal 3-3-1 model with only two Higgs triplets
The simplest non-Abelian gauge extension of the electroweak standard model, the SU(3){sub c} x SU(3){sub L} x U(1){sub N}, known as the 3-3-1 model, has a minimal version which demands the least possible fermionic content to account for the whole established phenomenology for the well-known particles and interactions. Nevertheless, in its original form the minimal 3-3-1 model was proposed with a set of three scalar triplets and one sextet in order to yield the spontaneous breaking of the gauge symmetry and generate the observed fermion masses. Such a huge scalar sector turns the task of clearly identifying the physical scalar spectrum into a clumsy labor. It not only adds an obstacle for the development of its phenomenology, but implies a scalar potential plagued with new free coupling constants. In this work, we show that the framework of the minimal 3-3-1 model can be built with only two scalar triplets, but still triggering the desired pattern of spontaneous symmetry breaking and generating the correct fermion masses. We present the exact physical spectrum and also show all the interactions involving the scalars, obtaining a neat minimal 3-3-1 model far more suited for phenomenological studies at the current Large Hadron Collider.
Left-right symmetric model with SU(2)-triplet fermions
We consider an SU(3){sub c} x SU(2){sub L} x SU(2){sub R} x U(1){sub B-L} left-right symmetric model with three Higgs scalars including an SU(2){sub L} doublet, an SU(2){sub R} doublet and an SU(2){sub L} x SU(2){sub R} bidoublet. In addition to usual SU(2)-doublet fermions, our model contains SU(2)-triplet fermions with Majorana masses. The neutral components of the left-handed triplets can contribute a canonical seesaw while the neutral components of the right-handed triplets associated with the right-handed neutrinos can contribute a double/inverse-type seesaw. Our model can be embedded into an SO(10) grand unification theory where the triplets belong to the 45=(1,3,1,0)+(1,1,3,0)+... representations.
Mixed-Spin Pairing Condensates in Heavy Nuclei
We show that the Bogoliubov-de Gennes equations for nuclear ground-state wave functions support solutions in which the condensate has a mixture of spin-singlet and spin-triplet pairing. We find that such mixed-spin condensates do not occur when there are equal numbers of neutrons and protons, but only when there is an isospin imbalance. Using a phenomenological Hamiltonian, we predict that such nuclei may occur in the physical region within the proton dripline. We also solve the Bogoliubov-de Gennes equations with variable constraints on the spin-singlet and spin-triplet pairing amplitudes. For nuclei that exhibit this new pairing behavior, the resulting energy surface can be rather soft, suggesting that there may be low-lying excitations associated with the spin mixing.
Singlet-triplet Hamiltonian for spin excitations in a Kondo insulator
In the nonsymmetric version of the periodic Anderson model for a Kondo insulator, an effective singlet-triplet Hamiltonian H{sub s-t} with indirect antiferromagnetic f-f exchange is constructed, which makes it possible to analyze the dynamic magnetic susceptibility {chi}{sub f}(k, {omega}) of f electrons. Hamiltonian H{sub s-t} is used to describe the experimentally observed dispersion of the three-level spin excitation spectrum in YbB{sub 12}. A distinguishing feature of this analysis is the introduction of small-radius singlet and triplet collective f-d excitations that form low- and high-lying spin bands during motion over the lattice.
Time dependence of the Hanle effect in the emission of triplet bound excitons in gallium selenide
The dynamics of the magnetic-field-induced depolarization of the circularly polarized radiation of spin-oriented triplet bound excitons in uniaxial crystals has been studied by time-resolved spectroscopy on an example of GaSe. The depolarization of radiation (the Hanle effect) is due to the difference between the behaviors of its {sigma}{sup +} and {sigma}{sup -} components in a magnetic field. It has been found that the magnetic-field dependences of the {sigma}{sup +} and {sigma}{sup -} component intensities vary considerably within the lifetime t of the excited states. The form of the magnetic-field dependence of the degree of polarization of the exciton radiation remains generally the same for various t values. A theoretical description of these effects has been proposed.
Determination of low-energy parameters of neutron-proton scattering in the the shape-parameter approximation from present-day experimental data
On the basis of the total cross sections for neutron-proton scattering in the region of laboratory energies below 150 keV, the value of {sigma}{sub 0} = 20.4288(146) b was obtained for the total cross sections for neutron-proton scattering at zero energy. This value is in very good agreement with the experimental cross sections obtained by Houke and Hurst, but it is at odds with Dilg's experimental cross section. By using the value that we found for {sigma}{sub 0} and the experimental values of the neutron-proton coherent scattering length f, the deuteron binding energy {epsilon}{sub t}, the deuteron effective radius {rho}{sub t}(-{epsilon}{sub t}, -{epsilon}{sub t}), and the total cross section in the region of energies below 5 MeV, the following values were found in the shape-parameter approximation for the low-energy parameters of neutron-proton scattering in the spin-triplet and spin-singlet states: a{sub t} = 5.4114(27) fm, r{sub 0t} = 1.7606(35) fm, v{sub 2t} = 0.157 fm{sup 3}, a{sub s} = -23.7154(80) fm, r{sub 0s} = 2.706(67) fm, and v{sub 2s} = 0.491 fm{sup 3}.
Multiple Slater Determinants and Strong Spin-Fluctuations as Key Ingredients of the Electronic Structure of Electron- and Hole-Doped Pb 10− x Cu x (PO 4 ) 6 O
LK-99, with chemical formula Pb 10−x Cu x (PO 4 ) 6 O, was recently reported to be a room-temperature superconductor. While this claim has met with little support in a flurry of ensuing work, a variety of calculations (mostly based on density-functional theory) have demonstrated that the system possesses some unusual characteristics in the electronic structure, in particular flat bands. We have established previously that within DFT, the system is insulating with many characteristics resembling the classic cuprates, provided the structure is not constrained to the P3(143) symmetry nominally assigned to it. Here we describe the basic electronic structure of LK-99 within self-consistent many-body perturbative approach, quasiparticle self-consistent GW (QSGW) approximation and their diagrammatic extensions. QSGW predicts that pristine LK-99 is indeed a Mott/charge transfer insulator, with a bandgap gap in excess of 3 eV, whether or not constrained to the P3(143) symmetry. When Pb 9 Cu(PO 4 ) 6 O is hole-doped, the valence bands modify only slightly, and a hole pocket appears. However, two solutions emerge: a high-moment solution with the Cu local moment aligned parallel to neighbors, and a low-moment solution with Cu aligned antiparallel to its environment. In the electron-doped case the conduction band structure changes significantly: states of mostly Pb character merge with the formerly dispersionless Cu d state, and high-spin and low spin solutions once again appear. Thus we conclude that with suitable doping, the ground state of the system is not adequately described by a band picture, and that strong correlations are likely. Irrespective of whether this system class hosts superconductivity or not, the transition of Pb 10 (PO 4 ) 6 O from being a band insulator to Pb 9 Cu(PO 4 ) 6 O, a Mott insulator, and multi-determinantal nature of doped Mott physics make this an extremely interesting case-study for strongly correlated many-body physics.
Comment on "Properties of (26)Mg and (26)Si in the sd shell model and the determination of the (25)Al(p,gamma) (26) Si reaction rate"
A recent discussion of theoretical work on the {sup 25}Al(p,{gamma}){sup 26}Si astrophysical reaction rate [W.A. Richter, B. Alex Brown, A. Signoracci and M. Wiescher Phys. Rev. C 83 065803 (2011)] omits some current and relevant experimental information in forming its scientific conclusions. Accounting for this new information has the potential to significantly alter the reaction rate derived in the paper.