O-31. On Peccei-Quinn symmetry and quark masses

H.T.Hung(1), V.N.Huyen(2), N.H.Thao(1), P.V.Dong(2) and H.N.Long(2)

We show that there is an infinite number of U(1) symmetries like Peccei-Quinn symmetry in the 3-3-1 model with minimal scalar sector. Moreover, all of them are completely broken due to the gauge symmetry breaking with the model's scalars. There is no any residual Peccei-Quinn symmetry. Because of the minimal scalar content there are some quarks that are massless at tree-level, but they can get consistent mass contributions at one-loop due to this fact.

Cao Hoang Nam(1), Ha Thanh Hung(2), Dinh Phan Khoi(3), Phung Van Dong(1)

We study the neutron anomalous magnetic moment (AMM) in a five dimensional gauge-Higgs unification scenario compactified on $ M^4 \times S^1/Z_2 $ with the bulk gauge symmetric group $ SU(3)_C \times SU(3)_L \times U(1)_X $. The detailed calculation for the neutron AMM by the exchange of KK modes of gauge bosons, their scalar partners, Higgs bosons and quarks will be performed at the one loop level.

P. V. Dong(1), H. N. Long(1) and V. V. Vien(2)

We propose two 3-3-1 models based on S_3 and S_4 flavor symmetries responsible for fermion masses and mixings.

Tran Huu Phat(1) and Nguyen Van Thu(2)

The chiral phase transition of linear sigma model with constituent quarks at finite temperature and chemical potential is crutinized in a non-simply connected space-time where the compactified dimension with length is taken along the $Oz$ direction. It results that corresponding to untwisted and twisted quarks the phase diagrams in the $(T, a)$-plane are quite different from each other. Here, untwisted (twisted) quark denotes the quark field which satisfies the periodic (anti-periodic) boundary conditions and $a= 1/L$. In the chiral limit the chiral phase transition for untwisted quark is first-order for all values of $a$, while for twisted quark it is first-order at low $a$ and becomes second-order at higher values of $a$. In the physical world with explicit symmetry breaking, it is found that the chiral phase transition for untwisted quark is first order at high values of $a$ and eventually ends up with a critical end point at low $a$, and for twisted quark it is the crossover transition everywhere.

Vu Van Hung(1), Hoang Thi Giang(1) and Pham Thi Minh Hanh(2)

Thermodynamic properties of bilayer graphene are investigated using the moment method in statistical (SMM) dynamics taking into account the anharmonicity effects of the lattice vibrations. The nearest neighbor distance, thermal expansion coefficient, specific heat at the constant volume and Young modulus of the bilayer graphene are calculated as a function of the temperature. .In the present study, the influence of temperature on the thermodynamic quantities of graphene and bilayer graphene have also been studied, using three different interatomic potentials. We discuss the temperature dependence of the thermodynamic quantities of the graphene and bilayer graphene and compare our calculated results with those of the experimental results.and other theories.

Tran Phuoc Duy, Vo Van Hoang

Heterogeneous melting used to be proposed to initial from the surface until the total melting. Recently, we have done intensive computation of heterogeneous melting and found that not only the pre-melting taken place sooner than the melting point, but also homogeneous melting takes place inside the models. Moreover, we found the free surface effects on the heterogeneous melting of the models. The larger the free surface is, the more heterogeneous the melting is, but the less homogeneous it is.

Vo Van On(1) and Tran Trong Nguyen(2)

In this paper, we introduce a f(R) gravity model with Lagrangian of polynomial – exponential form of scalar curvature R. We also point out that this f (R) gravity model can describe a universe with an accelerating phase of expansion at late time , it has the cosmological viability and also passes local tests in Solar system

Hoang Thanh Phi Hung(1), Nguyen Luong Quang(2) and Arabindo Roy(2)

The early phases of star formation are obscured by high level of interstellar dust which can be probe in emission at infrared wavelengths. We study the dusty environment around star-forming cores with new data from infrared space telescopes (Herschel, Spitzer, Akari and WISE) in order to infer the evolutionary phases of the star forming cores. We then suggest an evolutionary sequences of star formation which start with interstellar turbulence, which lead to filament formation and finally to core formation

Nguyen Tri Lan

A microscopic derivation of three-component Ginzburg-Landau (GL) field theory and the conditions of its validity in ferromagnetic superconductors are presented. The conditions when microscopically derived or phenomenological GL models fail and a microscopic description should be resorted, are also investigated. The investigation shows that three-component GL model can be used for addressing a wide range of questions in multiphase coexistence systems, in particular vortex physics and magnetic response.

Nguyen Duc Quyen(1), Ngo Van Thuyen(1), Nguyen Quang Hoc(2) and Nguyen Duc Hien(3)

Inverted pendulum is an unstable and highly nonlinear system. It is used as a common model for applications in linear and nonlinear control engineering. This paper presents the physical structure, the kinetic model of rotary Inverted pendulum system and the method of identifying and controlling this system by an artificial neural network. This network is a mathematical model based on the structure and the function of biological neural network. This is a state-of-the-art method of controlling which has many advantages such as the control of nonlinear objects, the ability of learning and accumulating experiences and the adjustment for changes of any parameter in the system

Tran Cong Phong(1), Do Thien Diep(2), Phan Nguyen Tuan(2), Vo Thanh Lam(3)

A theory of phonon-assisted cyclotron resonance (PACR) in semiconductor superlattices (SSL) is presented. Using operator projection technique, expressions for absorption powers are obtained when the electrons are scattered by polar optical phonons in SSL. Extra peaks in the absorption spectrum due to transitions between Landau levels accompanied by emission and absorption of phonons are predicted and can be found in numerical results for GaAs materials. The results show that the intensities of the PACR peaks are directly proportional to the strength of the electron-phonon interaction. These intensities are strong enough to be detected in cyclotron resonance experiments. Hence, by studying the intensity of PACR peaks, one can directly determine the strength of the electron-phonon interaction.

Nguyen Thi Thuy and Tran Minh Tien

Effects of electron correlations on a topological insulating phase are studied within a combination of the Haldane and the Falicov - Kimball model. The Haldane model provides the existence of topological insulating phase, while electron correlations are the essence of the Falicov - Kimball model. A mean field approximation is adopted to investigate the combined model. There is a competition between the trivial topological charge-ordered phase and topological insulating phase. A phase diagram is also presented.

D. T. Huong(1), H. P. Thao(2), B. T. L. Quyen(3), N. T. L. Hoai(1) and N. A. Viet(1)

The electrostatic potential profile of a spherical soft particle was derived by analytically solving the Poisson-Boltzmann equations on a spherical coordinate. The soft particle was assumed to consist of a point charged hard core and a charged outer layer. The problem was solved at the low charge approximation, the continuity of the potential and of the electric displacement field were applied as the boundary conditions. The contribution of the core to the potential profile was investgated with various values of its charge and its dielectric constant. The presence of charged-core strongly modified the local potential (within the particle). The surface potential and the potential distribution in the salt solution were found to be independent of the core dielectric constant and weakly dependent on the core charge.

Le Hoang Anh(1), Ho Sy Ta(2), and Do Van Nam(3)

The operation and the performance of top-gated sub-100 nanometer semiconducting graphene field-effect transistors are reported by considering appropriately the issue of graphene-metallic lead coupling. By assuming the physisorption contacts between the source/drain electrodes and the graphene channel the formation of the source and drain regions due to the charge transferred effect at the two ends of the channel was reproduced. The current-voltage characteristics were then calculated. It is found that the current depends on the gate voltage via the exponential law for samples with channel lengths shorter than 40 nm, but for samples with longer channels the ambipolar behavior is observed. Particularly, the current saturation with a rather small output conductance of 126 S/m is realized in a sufficiently large range of drain voltage due to the dominance of the thermionic emission and conventional tunneling mechanisms to the band-to-band tunneling one. A rough assessment of the device performance was also carried out. It reveals an extremely high cutoff frequency in the order of 103 GHz and a linear scaling rule for transistors with the channel length longer than 40 nm. The behavior and magnitude of these quantities are very consistent with a recent experimental study for sub-100 nm devices fabricated by using the selfalignment technique.

Mai Thi Lan, Pham Thai Binh, Nguyen Van Hong, Pham Khac Hung

Ha Noi University of Sciences & Technology

The diffusion in one-dimensional disordered lattice has been studied using kinetic Monte-Carlo method. The simulation has been conducted for a chain consisting of 4000 sites with periodic boundary conditions. The site and transition energies are adopted in accordance to Gauss distribution. We consider three type lattices: the site disordered lattice; transition disordered lattice and combined lattice. Furthermore we focus on the influence of energetic disorder and particle’s concentration on diffusivity. In particular, the blocking effect concerning existence of many particles has been clarified under different temperature and energetic conditions.

Duc-Anh Le(1), Anh-Tuan Hoang(2)

We investigate the Mott transition in the half-filled asymmetric Hubbard model with an on-site Coulomb repulsion $U$ and a spin-dependent hopping integral $t_\sigma$ by means of the coherent potential approximation. We found that the two spin species undergo the Mott transition simultaneously at a certain critical value $U_C$. We also compute density of states, the double occupation and characterize their behavior in the different phases. Our results are in good agreement with the recent dynamical mean-field theory predictions.

Duc-Anh Le(1), Anh-Tuan Hoang(2)

Using coherent potential approximation we study zero-temperature Mott transition of the half-filled Hubbard model in a two-dimensional square lattice with geometrical frustration. It turns out that the geometrical frustration reduces the gap between the Hubbard bands. As a result the metallic phase is stabilized up to a fairly large value of the on-site Coulomb interaction. We found that the critical value $U_C$ for the Mott transition is enhanced by the geometrical frustration. Our results are in good agreement with the ones obtained by the single-site dynamical mean-field theory.

Le Minh Thu and Bui Duc Tinh

In this paper we theoretically study the effect of size dispersion on the averaged magnetic susceptibility of ensembles of three-dimensional asymmetrical InGaAs/GaAs quantum rings. We use the effective one-electronic-band Hamiltonian with smooth three-dimensional confinement potential mapping the actual geometrical and material composition of the rings. Our efficient mapping method allows us to find energy states of the electrons confined in three-dimensional semiconductor quantum rings with very complex geometries. Then, we are able to calculate the magnetic susceptibility of an individual single electron nano-ring with fixed geometrical and material parameters. Considering dispersion of the ring's rim radius, we simulate combined homogeneous and inhomogeneous broadening of the averaged magnetic susceptibility of the ensembles of semiconductor quantum rings. The averaged magnetic susceptibility of the rings' ensembles demonstrates stable temperature dependence unlike an individual ring's magnetic susceptibility. Our simulation results are in a good agreement with the experimental observations.

Nguyen Thanh Tien(1) and Vo Huu Cau(2)

We present a theoretical study on the mobility of two-dimensional electron gas (2DEG) in non-doping Zn-polar ZnO/MgZnO heterostructure. We investigate the role of all possible scattering mechanisms affect to the mobility of two-dimensional electron gas exist in this structure. We show that the alloy disorder (AD) and polar surface roughness (PSR) scattering are two key scattering mechanisms affect to the mobility of 2DEGs in non-doping Zn-polar ZnO/MgZnO heterostructure. Our theory is able to explain experimental data about the 2DEG mobility dependence on the electron density at low-temperature.

Do Thi Nga, Chu Thuy Anh, To thi Thao, Ngo Van Thanh and Nguyen Ai Viet

We present a new method of trapping cold atoms using a silicon nanopillar. With this method, the cold atom moving near a silicon nanopillar is captured by sending the strong electromagnetic field through the silicon nanopillar. This field generates an evanescent wave around the silicon nanopillar. By evanescent effect, the wave decays away from the silicon nanopillar producing an attractive optical potential for trapping neutral atom. We consider some possible boundary conditions leading to the non-trivial bound state solution. Our result is also compared to the two most recent models concerning trapping of cold atoms by using a single wall carbon nanotube and an optical fiber.

Nguyen Van Nghia(1), Dinh Quoc Vuong(2), and Nguyen Quang Bau(3)

The acoustoelectric current in a rectangular quantum wire with an infinite potential is calculated by using the quantum kinetic equation for the distribution function electrons interacting with internal and external phonons. The analytic expression for the acoustoelectric current in the rectangular quantum wire with an infinite potential is obtained. The dependence of the expression for the acoustoelectric current on the temperature of the system T, the acoustic wave number q and the parameters of the rectangular quantum wire with an infinite potential are obtained. The theoretical results are numerically evaluated, plotted and discussed for the specific rectangular quantum wire with an infinite potential GaAs. The results are compared with those for normal bulk semiconductors to show difference.

M. Chung Nguyen(1), V. Hung Nguyen(1,2), and H. Viet Nguyen(1)

Motivated by recent experiments [1,2] on the bandgap engineering in graphene, we have considered the formation of bandgap and the transport in graphene nanomesh (GNM) based structures using atomistic quantum simulation within a tight binding model [3]. The formation of bandgap opening has been investigated in the lattices with different nanohole shapes, lattice parameters, and with disorder effects. It was shown that (i) in perfect GNM lattices the dependence of the bandgap on structural parameters is more complicated than that previously reported in literature [4,5], and (ii) with the presence of disorders all GNM lattices become semiconducting which is in line with experimental observations. Our studies suggest that the GNM lattices offer various possibilities of improving the transport properties such as, for instance, high On/Off current ratio and strong negative differential resistance in graphene devices.

Nguyen Quang Hoc(1), Nguyen Ngoc Anh(2), Nguyen The Hung(2), Nguyen Duc Hien(2) and Nguyen Duc Quyen(3)

The analytic expression of molar specific heat under constant volume of molecular cryocrystals of nitrogen type with hcp structure is obtained by the statistical moment method and the self-consistent field method taking account of the anharmonicity in lattice vibrations and molecular rotational motion. Numerical results for molecular cryocrystals of N2 type (N2, CO) are compared with experiments.