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In this work, we investigate the dynamics of a scalar field in the nonintegrable $\displaystyle \phi ^{4}$ model, restricted to the half-line. Here we consider singular solutions that interpolate the Dirichlet boundary condition $\phi(x=0,t)=H$ and their scattering with the regular kink solution. The simulations reveal a rich variety of phenomena in the field dynamics, such as the formation of a kink-antikink pair, the generation of oscillons by the boundary perturbations, and the interaction between these objects and the boundary, which causes the emergence of boundary-induced resonant scatterings (for example, oscillon-boundary bound states and kink generation by oscillon-boundary collision) founded into complex fractal structures. Linear perturbation analysis was applied to interpret some aspects of the scattering process. We detected the presence of two shape modes near the boundary. The power spectral density of the scalar field at a fixed point leads to several frequency peaks. Most of them can be explained with some interesting insights for the interaction between the scattering products and the boundary., Comment: 22 pages, 10 figures. This version accepted for publication in JHEP

We consider an extended model with two real scalar fields, $\phi(x,t)$ and $\chi(x,t)$. The first sector is controlled by the sine-Gordon superpotential, while the second field is submitted to the $\chi^4$ one. The fields mutually interact via a nontrivial coupling function $f(\chi)$ that also changes the kinematics of $\phi$. We briefly review the implementation of the Bogomol'nyi-Prasad-Sommerfield (BPS) prescription. We then solve the resulting BPS equations for two different interactions $f$. The first one leads to a single kink-kink configuration, while the second one gives rise to a inhomogeneous sine-Gordon kink lattice. We study the linear stability of these new solutions, focusing on their translational modes. We also explore how the strength of the mutual interaction affects the BPS profiles. In particular, we show that a homogeneous lattice with identical kinks is attained in the regime of extremely strong interactions., Comment: 18 pages, 3 figures. Suggestions are welcome

In this paper, we present topological defects in $(1,1)$ dimensions, described by an extended nonlinear $O(3)$ sigma model. We consider spherical coordinates $(\phi,\chi)$ in the $S^2$ isotopic space and a potential $V(\phi,\chi)$. For specific forms of the potential, it is possible to apply the Bogomol'nyi method, resulting in first-order equations of motion with solutions that minimize energy. We study a model with an explicit solution for the field $\phi$ that resembles the ubiquitous sine-Gordon kink/antikink, but with an internal structure given by the field $\chi$ with a form antilump/lump that depends on a constant $C$. The soliton-antisoliton scattering process depends on $C$ and on the initial velocity of the pair. Some results are reported, such as: one-bounce scattering for $\phi$, or strong emission of radiation for $\phi$, followed by i) annihilation of $\chi$; ii) same pattern antilump-antilump or lump-antilump for $\chi$; iii) inversion antilump-antilump to lump-lump for $\chi$; iv) inversion antilump-lump to lump-antilump for $\chi$. Other findings are: v) annihilation of the pair soliton-antisoliton with the emission of scalar radiation; vi) emission of pairs of oscillations around the vacuum for $\phi$ and $\chi$. The energy density shows that the defect has an internal structure as a nested defect of an antilump inside a kink. The lump core of the defect is responsible for the emission of radiation. The changing of structure of the defects during the scattering is analyzed not only with the field profiles in the physical $(1,1)$ space, but also in the internal $S^2$ space, which gives some new insight into the process., Comment: 27 pages, 14 figures

The Yukawa coupling of fermions with a periodic bosonic background is shown to give rise to several bound states to the fermionic spectrum, with some bound states gluing together around specific energy eingenvalues as the Yukawa coupling increases. This effect induces the presence of degenerate energy states inside the fermionic gap and may be of current interest., Comment: to appear in EPJ C as a letter

The strong coupling of plasmonic resonance modes in conductive pyramidal nanoparticles leads to an increase in the density of free charges on the surface. By ensuring plasmonic coupling in the pyramidal nanoparticle lattice, the achieved field intensity is potentiated. At the same time, a strong coupling between resonant modes is guaranteed, which results in the formation of new hybrid modes. In this manuscript, we demonstrated a tunable double anticrossing interaction that results from the interaction between two Localized Surface Plasmon Resonance (LSPR) modes and a Surface Plasmon Polariton (SPP) wave. The tuning is done as a function of the variation of the angle of incidence of the input electric field. From the double anticrossing, an increase in field intensity in a blue-shifted LSPR mode located in the red wavelength region is observed. This demonstrates that at certain angles of incidence, the intensity field obtained is strongly favored, which would be beneficial for applications such as Surface Enhancement Raman Spectroscopy (SERS). Nanoparticle-based lattices have been widely used for biosensor applications. However, one of the major limitations of this type of device is the low tolerance to high concentrations of biomolecules, which significantly affects their performance. According to the studies carried out for this manuscript, it was demonstrated that the implemented geometry allows for the observation of an LSPR mode, which is responsible for the control and synchronization of other perceived resonances. This mode remains almost invariant when subjected to structural variations or changes in the angle of incidence of the electric field. These characteristics eliminate the limitation mentioned above, allowing for sensitivities 10^3 times higher than those achieved in conventional systems based on LSPR used to detect P. brasiliensis antigen., Comment: 21 pages, 3 figures

We examine the oscillon decay in a model with a single scalar field and two asymmetric fundamental states. Specifically, we verify how the evolution of an initially excited oscillon leads to the formation of antikink-kink pairs in the presence of a centered long-lived pulse. In such a context, the magnitude of the original perturbation stands for the most important factor influencing the process. For intermediary values of this magnitude, we find a transitory behavior which suggests that the energy exchange between translational and vibrational modes begins to play an important role in the overall evolution. As the magnitude increases, the centered pulse intermediates an interaction between the inner structures which compose the pairs whose behavior mimics that of a standard antikink-kink collision and therefore reinforces the role played by the energy transfer mechanism. We depict the resulting resonant structure and note that it mimics that of an usual kink-antikink scattering. We also reproduce some of our results now via an initial lumplike perturbation proposed as a kink-antikink pair. For different values of width, {\it{an almost pure}} antikink-kink pair escapes to the infinity after multiple bounces., Comment: We have added a new section and figures

Higher-order scalar field models in two dimensions, including the $\phi^8$ model, have been researched. It has been shown that for some special cases of the minima positions of the potential, the explicit kink solutions can be found. However, in physical applications, it is very important to know all the explicit solutions of a model for any minima position. In the present study, with the help of some deformation functions, we have shown that higher-order scalar field theories can be obtained with explicit kinks. In particular, we introduced two deformation functions that, when applied to the well known $\phi^4$ and $\phi^6$ models, produce modified $\phi^8$ and $\phi^{10}$ models, respectively, with all their explicit kink-like solutions which depend on a single parameter. Since this parameter controls the position of the minima of the potential, we have found interesting new solutions in many distinct cases. We have also studied the kink mass, the behavior of the excitation spectra and several kink-antikink collisions for these two new modified models. The collision outcome is determined by the initial configuration, specifically the sequence in which the kink-antikink and antikink-kink pairings emerge. Another interesting finding is the suppression of resonance windows, which may be explained by the presence of a set of internal modes in the model., Comment: Version accepted for publication

We investigate kink-antikink collisions in a model characterized by two scalar fields in the presence of geometric constrictions. The model includes an auxiliary function that modifies the kinematics associated with one of the two fields. An important fact is that one of the fields can be solved independently, being responsible for changing the internal structure of the second one. We performed several collisions and observed the presence of resonance windows for small values of the parameters. Furthermore, we have been able to show the alternation between the appearance of oscillating pulses, as well as the annihilation and formation of kink-antikink pairs when the geometric constriction is more pronounced. The study of kink dynamics in models with geometric constrictions is connected with issues of interest such as domain wall formation and magnetization at the manometric scale., Comment: 30 pages, 17 figures, final version to be published in JHEP

Two hyperbolic-deformed field theoretic models are discussed. In both of them, due to the effect of specific deformation function on the well known $\varphi^4$ and $\varphi^6$ models, their internal structure may change significantly. Unlike the $\varphi^4$ kinks solutions, which has only one internal mode in addition to its translational mode, the kinks of the hyperbolic-deformed $\varphi^4$ model can have several internal modes. Moreover, the deformation on the $\varphi^6$ model has other interesting features, because the kinks of the $\varphi^6$ model have only a zero mode and the deformation may cause the appearance of internal mode for both kink and antikink. The presence of the new internal modes modify the collisions which we explore in the present work. The deformation relies on a real parameter, which controls the number of internal modes, and we also study how the deformation parameter alter the mass of the kinks and the critical velocities involved in the collisions., Comment: Accepted for publication in Chaos, Solitons and Fractals

This work deals with bifurcation and the chaotic behavior in one dimensional chains of small particles. We consider two distinct possibilities, one where the particles are modeled by a fourth-order potential which was already studied. We revisit this system and bring novelties concerning the presence of the three-armed star behavior and the study of the corresponding Lyapunov exponent. The other system is new, and there the particles are more involved and modeled by an eighth-order potential. We investigate this new system within the same approach, emphasizing the behavior of the orbits, the bifurcation profile and the corresponding Lyapunov exponent., Comment: Accepted for publication in Chaos, Solitons and Fractals