Isospin Components Research Articles

Kekulé-induced valley birefringence and skew scattering in graphene

In graphene, a Kekul\'e-Y bond texture modifies the electronic band structure generating two concentric Dirac cones with different Fermi velocities lying in the {\Gamma}-point in reciprocal space. The energy dispersion results in different group velocities for each isospin component at a given energy. This energy spectrum combined with the negative refraction index in p-n junctions, allows the emergence of an electronic analog of optical birefringence in graphene. We characterize the valley birefringence produced by a circularly symmetric Kekul\'e patterned and gated region using the scattering approach. We found caustics with two cusps separated in space by a distance dependent on the Kekul\'e interaction and that provides a measure of its strength. Then, at low carrier concentration we find a non-vanishing skew cross section, showing the asymmetry in the scattering of electrons around the axis of the incoming flux. This effect is associated with the appearance of the valley Hall effect as electrons with opposite valley polarization are deflected towards opposite directions.

Prompt production of the hidden charm pentaquarks in the LHC

Motivated by the observation of the first hidden charm pentaquarks by the LHCb collaboration in 2015 and the updated analysis with an order-of-magnitude larger data set in 2019, we estimate their cross sections for the prompt production as well as their heavy quark spin partners, in the Sigma _c^{(*)}bar{D}^{(*)} hadronic molecular picture, at the center-of-mass energy 7~text {TeV} in the pp collision. Their cross sections are several {mathrm {nb}} and we would expect several tens hidden charm pentaquark events in the LHC based on its current integrated luminosity. The cross sections show a sizable deviation of the cross sections for hidden charm pentaquarks with the third isospin component I_z=+frac{1}{2} (P_c^+) from those with I_z=-frac{1}{2} (P_c^0). The cross sections decrease dramatically with the increasing transverse momentum. Our study can also tell where to search for the missing hidden charm pentaquarks. The confirmation of the complete hidden charm pentaquarks in the heavy quark symmetry would further verify their Sigma _c^{(*)}bar{D}^{(*)} molecular interpretation. In addition, the relative strength among these cross sections for pentaquarks can help us to identify the quantum numbers of the P_c(4440) and P_c(4457).

Nagaoka spin-valley ordering in silicene quantum dots

We study a cluster of quantum dots defined within silicene that host confined electron states with spin and valley degrees of freedom. Atomistic tight-binding and continuum Dirac approximation are applied for few-electron system in quest for spontaneous valley polarization driven by inter-dot tunneling and electron-electron interaction, i.e. a valley counterpart of itinerary Nagaoka ferromagnetic ordering recently identified in GaAs square cluster of quantum dots with three excess electrons [P. Dehollain, {\it et al.}, Nature {\bf 579}, 528 (2020)]. We find that for Hamiltonian without intrinsic-spin orbit coupling -- similar to the one of graphene with staggered potential -- the valley polarization in the ground-state can be observed in a range of inter-dot spacing provided that the spin of the system is frozen by external magnetic field. The inter-valley scattering effects are negligible for cluster geometry that supports the valley polarized ground-state. In presence of a strong intrinsic spin-orbit coupling that is characteristic to graphene no external magnetic field is necessary for observation of ground-state that is polarized in both spin and valley. The effective magnetic field due to the spin-orbit interaction produces a perfect anticorrelation of the spin and valley isospin components in the degenerate ground-state.

Equation of state and correlation functions of hypernuclear matter within the lowest order constrained variational method

The lowest order constrained variational method is reformulated to find the equation of state of hypernuclear matter. For the nucleon-nucleon interaction we employed the well-known Argonne V18 (AV18) interaction. The equation of state is calculated using two-body central potentials for $\mathrm{\ensuremath{\Lambda}}N$ and $\mathrm{\ensuremath{\Lambda}}\mathrm{\ensuremath{\Lambda}}$ interactions that are determined in order to reproduce the experimental data on single- and double-$\mathrm{\ensuremath{\Lambda}}$ hypernuclei. For the odd-state part of the $\mathrm{\ensuremath{\Lambda}}\mathrm{\ensuremath{\Lambda}}$ interaction, which is not known due to the lack of experimental data, a proposed repulsive and attractive potential is employed to calculate the equation of state. It is shown that the presence of $\mathrm{\ensuremath{\Lambda}}$ in the hypernuclear matter produces a strong softening of the equation of state. The results are compared with similar calculations with another variational method. The state-dependent energy as well as central and tensor correlation functions are studied up to $J=2$ for each JLSTMT channel where related to total (J), orbital (L) and spin (S) angular momentum and isospin (T) and the third component of isospin (MT) respectively for $\mathrm{\ensuremath{\Lambda}}N$ and $\mathrm{\ensuremath{\Lambda}}\mathrm{\ensuremath{\Lambda}}$ interactions. Furthermore, the effect of baryon density and hyperon density as well as the type of hyperon-hyperon interaction on the two-body correlation functions are investigated.

Quantum Monte Carlo study of the S4 symmetric microscopic model for iron-based superconductors

The S4 symmetric microscopic model with two iso-spin components has been studied via constrained-path quantum Monte Carlo simulation. Our results demonstrate a stable (π, 0) or (0, π) magnetic order which is significantly enhanced on increasing both the Coulomb repulsion U and Hund’s coupling strength J. Also, our simulation indicates that the magnetic order tends to be in an orthomagnetic state, in which the nearest-neighbour magnetic moment are orthogonal to each other, rather than in a collinear antiferromagnetic order. Interestingly, when the system is doped away from half filling, the magnetic order is obviously elevated in the low doping density, and then significantly suppressed when more electrons are introduced. Meanwhile, we find that an A1gs±-wave pairing dominates all the singlet nearest-neighbour pairings, and is significantly enhanced by electron doping.

Two-loop corrections to the rho parameter in Two-Higgs-Doublet models

Models with two scalar doublets are among the simplest extensions of the Standard Model which fulfill the relation rho = 1 at lowest order for the rho parameter as favored by experimental data for electroweak observables allowing only small deviations from unity. Such small deviations varDelta rho originate exclusively from quantum effects with special sensitivity to mass splittings between different isospin components of fermions and scalars. In this paper the dominant two-loop electroweak corrections to varDelta rho are calculated in the CP-conserving THDM, resulting from the top-Yukawa coupling and the self-couplings of the Higgs bosons in the gauge-less limit. The on-shell renormalization scheme is applied. With the assumption that one of the CP-even neutral scalars represents the scalar boson observed by the LHC experiments, with standard properties, the two-loop non-standard contributions in varDelta rho can be separated from the standard ones. These contributions are of particular interest since they increase with mass splittings between non-standard Higgs bosons and can be additionally enhanced by tan beta and lambda _5, an additional free coefficient of the Higgs potential, and can thus modify the one-loop result substantially. Numerical results are given for the dependence on the various non-standard parameters, and the influence on the calculation of electroweak precision observables is discussed.

Constraints on the S=-1 meson-baryon interaction at NLO

This work contains a study of the meson-baryon interaction in the S = −1 sector by means of a chiral SU (3) Lagrangian up to next-to-leading order (NLO) and implementing unitarization in coupled channels. In order to get more reliable values of the parameters which are present in the model, we performed several fits which take a large set of experimental scattering data in different two-body channels, threshold branching ratios, and the precise SIDDHARTA values of the energy shift and width of kaonic hidrogen into consideration. In previous studies, we had shown that the K − p → K Ξ reactions are especially sensitive to the next to Weinberg-Tomozawa (WT) corrections in the hierarchy. In addition, we pointed out the need to employ processes which are described by pure isospin amplitudes as a tool to discern which models are more realistic among those which give small values for the χ 2 in the fits. Following the former suggestion, we present results which include data from K − p → η Λ, η Σ reactions which have pure isospin I = 0 and I = 1 component respectively. Finally, to check the goodness of the new obtained parametrization of the model, we present a prediction for another process that filters the I = 1 isospin component: the pure I = 1 reaction which could be measured at the proposed secondary K 0 L beam at Jlab.

The chiral S = −1 meson–baryon interaction with new constraints on the NLO contributions

We present a study of the S=−1 meson–baryon interaction, employing a chiral SU(3) Lagrangian up to next-to-leading order (NLO) and implementing unitarization in coupled channels. The parameters of the model have been fitted to a large set of experimental scattering data in different two-body channels, to threshold branching ratios, and to the precise SIDDHARTA value of the energy shift and width of kaonic hidrogen. In contrast to other groups, we have taken into consideration the K−p→K+Ξ−,K0Ξ0 reaction data, since we found in a previous work to be especially sensitive to the NLO parameters of the chiral Lagrangian. In the present work we also include the Born terms, which usually have very little effect, and find them to be non-negligible in the K−p→KΞ channels, correspondingly causing significant modifications to the NLO parameters. We furthermore show that the importance of the Born terms becomes more visible in the isospin projected amplitudes of the K−p→KΞ reactions. The measurement of processes that filter single isospin components, like the KL0p→K+Ξ0 reaction that could be measured at the proposed secondary KL0 beam at Jlab, would put valuable constraints on the chiral models describing the meson–baryon interaction in the S=−1 sector.

The $T_{z} = \pm 1 \to 0$ and $\pm 2 \to \pm 1$ Mirror Gamow--Teller Transitions in $pf$-shell Nuclei

Gamow–Teller (GT) transitions are the most common weak-interaction processes in the Universe. They play important roles in various processes of nucleosynthesis, for example, in the rapid proton-capture process (rp-process). In the pf-shell region, the rp-process runs through neutron-deficient nuclei with Tz = −2, −1, and 0 mainly by means of GT and Fermi transitions, where Tz is the z component of isospin T defined by Tz = (N − Z)∕2. Under the assumption of isospin symmetry, mirror nuclei with reversed Z and N numbers, and thus with opposite signs of Tz, have the same structure. Therefore, symmetry is also expected for the GT transitions starting from and ending up in mirror nuclei. We have been studying the Tz = −2 →−1 and −1 → 0 GT transitions in β decays, while those from stable Tz = +2 and +1 nuclei by means of hadronic (3He,t) charge-exchange (CE) reactions. The results from these studies are compared in order to examine the mirror-symmetry structure in nuclei. In addition, these results are combined for the better understanding of GT transitions in the pf-shell region.

Final state interaction in D + → K − π + π + with Kπ I = 1/2 and 3/2 channels

The final state interaction contribution to $D^+$ decays is computed for the $K^-\pi^+\pi^+$ channel within a light-front relativistic three-body model for the final state interaction. The rescattering process between the kaon and two pions in the decay channel is considered. The off-shell decay amplitude is a solution of a four-dimensional Bethe-Salpeter equation, which is decomposed in a Faddeev form. The projection onto the light-front of the coupled set of integral equations is performed via a quasi-potential approach. The S-wave $K\pi$ interaction is introduced in the resonant isospin $1/2$ and the non-resonant isospin $3/2$ channels. The numerical solution of the light-front tridimensional inhomogeneous integral equations for the Faddeev components of the decay amplitude is performed perturbatively. The loop-expansion converges fast, and the three-loop contribution can be neglected in respect to the two-loop results for the practical application. The dependence on the model parameters in respect to the input amplitude at the partonic level is exploited and the phase found in the experimental analysis, is fitted with an appropriate choice of the real weights of the isospin components of the partonic amplitude. The data suggests a small mixture of total isospin $5/2$ to the dominant $3/2$ one. The modulus of the unsymmetrized decay amplitude, which presents a deep valley and a following increase for $K\pi$ masses above $1.5$ GeV, is fairly reproduced. This suggests the assignment of the quantum numbers $0^+$ to the isospin 1/2 $K^*(1630)$ resonance.

The Cantor Set Constructed from an Infinite Number of Quarks Constituting the Nucleon and the Dark Matter

In a previous paper, the present author proposed the infinite sub-layer quark model, in which the proton and the neutron are composed of an infinite number of point-like (structure-less) quarks ?? and anti-quarks at an infinite sub-layer level. The limit particle ?? has all one-half quantum numbers of spin , isospin , third component of isospin , and fractional electric charge , where e is the electron charge. This fermion will behave as if it was lepton, since the baryon number vanishes at an infinite sub-layer level. Thus, this ultimate particle is considered as constituting the non-baryonic cold dark matter. A pair of an infinite number of ?? and quarks would be produced in the first moments after the Big Bang and form the nucleons and remain as the dark matter for all time, stable against decay. It was then shown that is violated in the doublet of ?? and quarks to account for the asymmetry of the number of particles and antiparticles in the present universe. Furthermore, it was shown that the Higgs bosons are composed of ?? and dark matter particles. In this paper, we will show that the Cantor set is constructed from an infinite number of point-like quarks ?? and anti-quarks which constitutes the nucleon and the dark matter. It is also shown that the color charges in quantum chromodynamics (QCD) of ?? and quarks vanish and these limiting particles of dark matter have no color force with the strong interaction and subject only to the weak interaction and gravity.

LHC phenomenology and cosmology of string-inspired intersecting D-brane models

We discuss the phenomenology and cosmology of a Standardlike Model inspired by string theory, in which the gauge fields are localized on D-branes wrapping certain compact cycles on an underlying geometry, whose intersection can give rise to chiral fermions. The energy scale associated with string physics is assumed to be near the Planck mass. To develop our program in the simplest way, we work within the construct of a minimal model with gauge-extended sector $U(3{)}_{B}\ifmmode\times\else\texttimes\fi{}Sp(1{)}_{L}\ifmmode\times\else\texttimes\fi{}U(1{)}_{{I}_{R}}\ifmmode\times\else\texttimes\fi{}U(1{)}_{L}$. The resulting $U(1)$ content gauges the baryon number $B$, the lepton number $L$, and a third additional Abelian charge ${I}_{R}$ which acts as the third isospin component of an $SU(2{)}_{R}$. All mixing angles and gauge couplings are fixed by rotation of the $U(1)$ gauge fields to a basis diagonal in hypercharge $Y$ and in an anomaly-free linear combination of ${I}_{R}$ and $B\ensuremath{-}L$. The anomalous ${Z}^{\ensuremath{'}}$ gauge boson obtains a string scale St\"uckelberg mass via a 4D version of the Green-Schwarz mechanism. To keep the realization of the Higgs mechanism minimal, we add an extra $SU(2)$ singlet complex scalar, which acquires a VEV and gives a TeV-scale mass to the nonanomalous gauge boson ${Z}^{\ensuremath{'}\ensuremath{'}}$. The model is fully predictive and can be confronted with dijet and dilepton data from LHC8 and, eventually, LHC14. We show that ${M}_{{Z}^{\ensuremath{'}\ensuremath{'}}}\ensuremath{\approx}3--4\text{ }\text{ }\mathrm{TeV}$ saturates current limits from the CMS and ATLAS Collaborations. We also show that for ${M}_{{Z}^{\ensuremath{'}\ensuremath{'}}}\ensuremath{\lesssim}5\text{ }\text{ }\mathrm{TeV}$, LHC14 will reach discovery sensitivity $\ensuremath{\gtrsim}5\ensuremath{\sigma}$. After that, we demonstrate in all generality that ${Z}^{\ensuremath{'}\ensuremath{'}}$ milliweak interactions could play an important role in observational cosmology. Finally, we examine some phenomenological aspects of the supersymmetric extension of the D-brane construct.

ISOSPIN SYMMETRY OF Tz = ±3/2 → ±1/2 GAMOW-TELLER TRANSITIONS IN A = 37 AND A = 41 NUCLEI

Under the assumption of good isospin symmetry, Tz = ±3/2 → ±1/2 Gamow-Teller (GT) transitions in a mass A isobar are analogous, where Tz is the z component of isospin T defined by 1/2(N - Z). We studied the Tz = +3/2 → +1/2 GT transitions by using the 37 Cl (3 He ,t)37 Ar and 41 K (3 He ,t)41 Ca reactions at E beam = 140 MeV / nucleon . The GT transition strengths in 37 Ar and 41 Ca were obtained up to the excitation energy (Ex) of 14.2 MeV and 10.4 MeV with energy resolutions of 30 and 35 keV, respectively. The obtained GT strengths were compared with those of the Tz = -2/3 → -1/2 mirror transitions, measured by the β-decay of 37 Ca and 41 Ti , respectively. It was found that the overall distributions of the mirror transitions were similar in both A = 37 and A = 41 systems. In A = 37 the differences seen at lower excitation energies are suggested to be the effect of the tensor interaction in the charge-exchange reaction. The differences seen at higher excitation energies are suggested to be the effect of the Coulomb interaction that can break the mirror symmetry of the strength distributions.

Fluctuations, strangeness, and quasiquarks in heavy-ion collisions from lattice QCD

We report measurements of diagonal susceptibilities for the baryon number, chi_B, electrical charge, chi_Q, third component of isospin, chi_I, strangeness, chi_S, and hypercharge, chi_Y, as well as the off-diagonal chi_BQ, chi_BY, chi_BS, etc. We show that the ratios of susceptibilities in the high temperature phase are robust variables, independent of lattice spacing, and therefore give predictions for experiments. We also investigate strangeness production and flavour symmetry breaking matrix elements at finite temperature. Finally, we present evidence that in the high temperature phase of QCD the different flavour quantum numbers are excited in linkages which are exactly the same as one expects from quarks. We present some investigations of these quark-like quasi particles.

Gamow-Teller Strengths in Proton-Rich Exotic Nuclei Deduced in the Combined Analysis of Mirror Transitions

Isospin symmetry is expected for the T(z)=+/-1-->0 isobaric analogous transitions in isobars with mass number A, where T(z) is the z component of isospin T. Assuming this symmetry, strengths of analogous Gamow-Teller (GT) transitions within A = 50 isobars were determined from a high energy-resolution study at 0 degrees in combination with the decay Q value and lifetime from the beta decay. This method can be applied to other pf-shell nuclei and can be used to study GT strengths of astrophysical interest.

A determination of electroweak parameters at HERA

Using the deep inelastic e+p and e−p charged and neutral current scattering cross sections previously published, a combined electroweak and QCD analysis is performed to determine electroweak parameters accounting for their correlation with parton distributions. The data used have been collected by the H1 experiment in 1994–2000 and correspond to an integrated luminosity of 117.2 pb−1. A measurement is obtained of the W propagator mass in charged current ep scattering. The weak mixing angle sin2θW is determined in the on-mass-shell renormalisation scheme. A first measurement at HERA is made of the light quark weak couplings to the Z0 boson and a possible contribution of right-handed isospin components to the weak couplings is investigated.

Baryon-baryon bound state in a 2+1 lattice QCD model with two flavors and strong coupling

We consider baryon-baryon bound states in $\mathrm{S}\mathrm{U}(3)$ lattice QCD with two flavors, $2\ifmmode\times\else\texttimes\fi{}2$ spin matrices in $2+1$ dimensions, and in an imaginary time formulation. For small hopping parameter $0<\ensuremath{\kappa}\ensuremath{\ll}1$ and large glueball mass, we show the existence of an isospin $3/2$ baryon, with asymptotic mass $\ensuremath{-}3\mathrm{ln}\ensuremath{\kappa}$ and isolated dispersion curve. Baryon-baryon bound states of isospin zero and one are found with approximate binding energy ${\ensuremath{\kappa}}^{2}/8$ and ${\ensuremath{\kappa}}^{2}/24$, respectively, using a ladder approximation to a Bethe-Salpeter equation. The baryon-baryon interaction associated with the ladder approximation is an energy independent spatial range-one attractive potential with an $\mathcal{O}({\ensuremath{\kappa}}^{2})$ strength. The attractive potential does not have a meson exchange interpretation. Six-point gauge field correlations give rise to attraction and counterbalance the Pauli repulsion to give a vanishing zero-range potential. The overall range-one potential results from a complicated interaction between the isospin components of the constituent quarks of the baryons.

Nucleon elastic scattering potentials: Energy and isospin dependence

Volume integrals of the real potentials derived from proton elastic scattering studies have been calculated for data available from the lowest to the highest energy. Because of the spread of the volume integrals at low energies, an average of volume integrals in each 1 MeV bin was calculated. These average volume integrals show a logarithmic dependence on the beam energy. A similar analysis of neutron potentials shows that the proton energy dependence can be applied to neutron data. The data for proton scattering from Ca isotopes at 1044 MeV were analyzed in terms of the optical model, and an isospin component of the potential was determined. The derived isospin potential is compared with those obtained for proton and neutron scattering in previous investigations.

Evolution of nuclear spectra with nuclear forces.

We first define a series of NN interaction models ranging from very simple to fully realistic. We then present Green's function Monte Carlo calculations of light nuclei to show how nuclear spectra evolve as the nuclear forces are made increasingly sophisticated. We find that the absence of stable five- and eight-body nuclei depends crucially on the spin, isospin, and tensor components of the nuclear force.

Lattice QCD at finite isospin density at zero and finite temperature

We simulate lattice QCD with dynamical $u$ and $d$ quarks at finite chemical potential, $\mu_I$, for the third component of isospin ($I_3$), at both zero and at finite temperature. At zero temperature there is some $\mu_I$, $\mu_c$ say, above which $I_3$ and parity are spontaneously broken by a charged pion condensate. This is in qualitative agreement with the prediction of effective (chiral) Lagrangians which also predict $\mu_c=m_\pi$. This transition appears to be second order, with scaling properties consistent with the mean-field predictions of such effective Lagrangian models. We have also studied the restoration of $I_3$ symmetry at high temperature for $\mu_I > \mu_c$. For $\mu_I$ sufficiently large, this finite temperature phase transition appears to be first order. As $\mu_I$ is decreased it becomes second order connecting continuously with the zero temperature transition.