arXiv subjects

Muneto Nitta

Publications and source records attributed to Muneto Nitta.

At least 253 records · Page 14Linked to original sources

arXiv2013

Non-Abelian statistics of vortices with non-Abelian Dirac fermions

We extend our previous analysis on the exchange statistics of vortices having a single Dirac fermion trapped in each core, to the case where vortices trap two Dirac fermions with U(2) symmetry. Such a system of vortices with non-Abelian Dirac fermions appears in color superconductors at extremely high densities, and in supersymmetric QCD. We show that the exchange of two vortices having doublet Dirac fermions in each core is expressed by non-Abelian representations of a braid group, which is explicitly verified in the matrix representation of the exchange operators when the number of vortices is up to four. We find that the result contains the matrices previously obtained for the vortices with a single Dirac fermion in each core as a special case. The whole braid group does not immediately imply non-Abelian statistics of identical particles because it also contains exchanges between vortices with different numbers of Dirac fermions. However, we find that it does contain, as its subgroup, a genuine non-Abelian statistics for the exchange of the identical particles, that is, vortices with the same number of Dirac fermions. This result is surprising compared with conventional understanding because all Dirac fermions are defined locally at each vortex, unlike the case of Majorana fermions for which Dirac fermions are defined non-locally by Majorana fermions located at two spatially separated vortices.

cond-mat.supr-con↗

arXiv2013

Jewels on a wall ring

We construct a stable domain wall ring with lump beads on it in a baby Skyrme model with a potential consisting of two terms linear and quadratic in fields.

hep-th↗

arXiv2013

Toroidal domain walls as Hopfions

We construct stable domain walls in a shape of a torus in the Faddeev-Skyrme model with a quadratic potential term admitting two discrete vacua. The phase modulus of the domain wall is twisted P and Q times along the toroidal and poloidal cycles of the torus, respectively, where Q represents the constituent lump charge. We find that these solutions carry the Hopf charge PQ and can be regarded as Hopfions. The toroidal domain walls are characterized by the two topological charges (P,Q), unlike the conventional Hopfions characterized by only the Hopf charge. We explicitly construct stable solutions of the toroidal domain walls with P, Q = 1,2,3, yielding the Hopf charges 1,2,3,4,6,9.

hep-th↗

arXiv2013

Non-Abelian Quasi-Gapless Modes Localized on Mass Vortices in Superfluid 3He-B

Kelvin waves or Kelvons have been known for a long time as gapless excitations propagating along superfluid vortices. These modes can be interpreted as the Nambu-Goldstone excitations arising from the spontaneous breaking of the translational symmetry. Recently a different type of gapless excitation localized on strings -- the so-called non-Abelian mode -- attracted much attention in high-energy physics. We discuss their relevance in condensed matter physics. Although we failed to find exactly gapless non-Abelian modes, non-Abelian rotational quasigapless excitations are argued to exist on the mass vortices in the B phase of the superfluid 3He, due to the fact that the order parameter in 3He-B is tensorial. While the U(1) rotational excitations are well established in vortices with asymmetric cores, the non-Abelian rotational excitations belonging to the same family were not considered. In the general case they are coupled with the translational modes.

cond-mat.other↗

arXiv2013

Self-consistent multiple complex-kink solutions in Bogoliubov-de Gennes and chiral Gross-Neveu systems

We exhaust all exact self-consistent solutions of complex-valued fermionic condensates in the 1+1 dimensional Bogoliubov-de Gennes and chiral Gross-Neveu systems under uniform boundary conditions. We obtain $n$ complex (twisted) kinks, or grey solitons, with $2n$ parameters corresponding to their positions and phase shifts. Each soliton can be placed at an arbitrary position while the self-consistency requires its phase shift to be quantized by $π/N$ for $N$ flavors.

cond-mat.supr-con↗

arXiv2013

Matryoshka Skyrmions

We construct a stable Skyrmion in 3+1 dimensions as a sine-Gordon kink inside a domain wall within a domain wall in an O(4) sigma model with hierarchical mass terms without the Skyrme term. We also find that higher dimensional Skyrmions can stably exist with a help of non-Abelian domain walls in an O(N) model with hierarchical mass terms without a Skyrme term, which leads a matryoshka structure of Skyrmions.

hep-th↗

arXiv2013

Wall-vortex composite solitons in two-component Bose-Einstein condensates

We study composite solitons, consisting of domain walls and vortex lines attaching to the walls in two-component Bose-Einstein condensates. When the total density of two components is homogeneous, the system can be mapped to the O(3) nonlinear sigma model for the pseudospin representing the two-component order parameter and the analytical solutions of the composite solitons can be obtained. Based on the analytical solutions, we discuss the detailed structure of the composite solitons in two-component condensates by employing the generalized nonlinear sigma model, where all degrees of freedom of the original Gross-Pitaevskii theory are active. The density inhomogeneity results in reduction of the domain wall tension from that in the sigma model limit. We find that the domain wall pulled by a vortex is logarithmically bent as a membrane pulled by a pin, and it bends more flexibly than not only the domain wall in the sigma model but also the expectation from the reduced tension. Finally, we study the composite soliton structure for actual experimental situations with trapped immiscible condensates under rotation through numerical simulations of the coupled Gross-Pitaevskii equations.

cond-mat.quant-gas↗

arXiv2013

Instantons confined by monopole strings

It is known that monopoles can be confined by vortex-strings in d=3+1 while vortices can be confined by domain-lines in d=2+1. Here, as a higher dimensional generalization of these, we show that Yang-Mills instantons can be confined by monopole-strings in d=4+1. We achieve this by putting the system into the Higgs phase in which the configuration can be constructed inside a non-Abelian vortex sheet.

hep-th↗

arXiv2013

D-brane solitons and boojums in field theory and Bose-Einstein condensates

In certain field theoretical models, composite solitons consisting of a domain wall and vortex lines attached to the wall have been referred to as D-brane solitons. We show that similar composite solitons can be realized in phase-separated two-component Bose-Einstein condensates. We discuss the similarities and differences between topological solitons in the Abelian-Higgs model and those in two-component Bose-Einstein condensates. Based on the formulation of gauge theory, we introduce the "boojum charge" to characterize the "D-brane soliton" in Bose-Einstein condensates.

cond-mat.quant-gas↗

arXiv2013

Brane Realization of Nambu Monopoles and Electroweak Strings

In the standard model, the electroweak Z-string can end on a Nambu monopole, whose mass is calculated to be 689 GeV from the current precise experimental data assuming the new particle with mass 125 GeV to be the Higgs boson. We study an extension of the standard model with additional singlet and triplet Higgs fields in the framework of N=1 supersymmetric field theory by using a D-brane configuration in type IIA string theory. We construct a D-brane configuration describing the electroweak symmetry breaking, and find a single D2-brane configuration describing a Z-string and a Nambu monopole attached by a Z-string in the standard model without an adjoint Higgs field. We further find a single D2-brane configuration describing a composite of a 't Hooft-Polyakov monopole and a Nambu monopole attached by a Z-string in an extended standard model with an adjoint Higgs field. We compute the binding energy of the 't Hooft-Polyakov and Nambu monopoles by solving a minimal surface area of a D2-brane.

hep-th↗

arXiv2013

Correspondence between Skyrmions in 2+1 and 3+1 Dimensions

A lump (2D Skyrmion) can be constructed as a sine-Gordon kink (1D Skyrmion) inside a domain wall in the massive O(3) sigma model. In this paper, we discuss relations between Skyrmions in 2+1 and 3+1 dimensions. We first construct a Bogomol'nyi-Prasad-Sommerfield 3D Skyrmion as a lump inside a non-Abelian domain wall in an O(4) sigma model with a potential term admitting two discrete vacua. Next, we construct a conventional 3D Skyrmion as a baby Skyrmion in a non-Abelian domain wall in the Skyrme model with a modified mass term admitting two discrete vacua. We also construct a spinning 3D Skyrmion as a Q-lump in the non-Abelian domain wall.

hep-th↗

arXiv2012

Colorful boojums at the interface of a color superconductor

We study junctions of vortices, or boojums, at the interface between color and hadronic superconducting/superfluid phases. This type of interface could be present in the interior of neutron stars, where an inner core made of quark matter in the color-flavor-locked phase is surrounded by an outer shell of superconducting protons and superfluid neutrons. We study the fate of magnetic (proton) and superfluid (neutron) vortices as they enter the color-flavor locked phase. We find that proton vortices terminate on Dirac monopoles of the massless magnetic field, and magnetic fluxes of massive gauge field spread along the surface and are screened by surface superconducting currents. On the other hand, three neutron vortices join at a boojum and split into three color magnetic vortices which host confined color-magnetic monopoles when strange quark mass is taken into account. We also present a simple numerical model of the shape of the neutron boojum.

hep-ph↗

arXiv2012

Tachyon Condensation Due to Domain-Wall Annihilation in Bose-Einstein Condensates

We show theoretically that a domain-wall annihilation in two-component Bose-Einstein condensates causes tachyon condensation accompanied by spontaneous symmetry breaking in a two-dimensional subspace. Three-dimensional vortex formation from domain-wall annihilations is considered a kink formation in subspace. Numerical experiments reveal that the subspatial dynamics obey the dynamic scaling law of phase-ordering kinetics. This model is experimentally feasible and provides insights into how the extra dimensions influence subspatial phase transition in higher-dimensional space.

cond-mat.quant-gas↗

arXiv2012

Josephson vortices and the Atiyah-Manton construction

We show that sine-Gordon solitons appear in the low-energy effective theory of a domain wall in a U(1) gauge theory with two charged complex scalar fields with masses, if we introduce the Josephson interaction term between the scalar fields. We identify these sine-Gordon solitons as vortices or CP(1) sigma model instantons in the bulk, which are absorbed into the domain wall world-volume. These vortices can be called as Josephson vortices since they appear in Josephson junctions of two superconductors. This set up gives a physical realization of a lower dimensional analogue of Atiyah-Manton construction of Skyrmions from instanton holonomy.

hep-th↗

arXiv2012

Tachyon Condensation and Brane Annihilation in Bose-Einstein Condensates: Spontaneous Symmetry Breaking in Restricted Lower-dimensional Subspace

In brane cosmology, the Big Bang is hypothesized to occur by the annihilation of the brane-anti-brane pair in a collision, where the branes are three-dimensional objects in a higher-dimensional Universe. Spontaneous symmetry breaking accompanied by the formation of lower-dimensional topological defects, e.g. cosmic strings, is triggered by the so-called `tachyon condensation', where the existence of tachyons is attributable to the instability of the brane-anti-brane system. Here, we discuss the closest analogue of the tachyon condensation in atomic Bose-Einstein condensates. We consider annihilation of domain walls, namely branes, in strongly segregated two-component condensates, where one component is sandwiched by two domains of the other component. In this system, the process of the brane annihilation can be projected effectively as ferromagnetic ordering dynamics onto a two-dimensional space. Based on this correspondence, three-dimensional formation of vortices from a domain-wall annihilation is considered to be a kink formation due to spontaneous symmetry breaking in the two-dimensional space. We also discuss a mechanism to create a `vorton' when the sandwiched component has a vortex string bridged between the branes. We hope that this study motivates experimental researches to realize this exotic phenomenon of spontaneous symmetry breaking in superfluid systems.

cond-mat.other↗

arXiv2012

Fermionic solutions of chiral Gross-Neveu and Bogoliubov-de Gennes systems in nonlinear Schrödinger hierarchy

The chiral Gross-Neveu model or equivalently the linearized Bogoliubov-de Gennes equation has been mapped to the nonlinear Schrödinger (NLS) hierarchy in the Ablowitz-Kaup-Newell-Segur formalism by Correa, Dunne and Plyushchay. We derive the general expression for exact fermionic solutions for all gap functions in the arbitrary order of the NLS hierarchy. We also find that the energy spectrum of the n-th NLS hierarchy generally has n+1 gaps. As an illustration, we present the self-consistent two-complex-kink solution with four real parameters and two fermion bound states. The two kinks can be placed at any position and have phase shifts. When the two kinks are well separated, the fermion bound states are localized around each kink in most parameter region. When two kinks with phase shifts close to each other are placed at distance as short as possible, the both fermion bound states have two peaks at the two kinks, i.e., the delocalization of the bound states occurs.

cond-mat.supr-con↗

arXiv2012

Spontaneous Magnetization through Non-Abelian Vortex Formation in Rotating Dense Quark Matter

When a color superconductor of high density QCD is rotating, superfluid vortices are inevitably created along the rotation axis. In the color-flavor locked phase realized at the asymptotically large chemical potential, there appear non-Abelian vortices carrying both circulations of superfluid and color magnetic fluxes. A family of solutions has a degeneracy characterized by the Nambu-Goldtone modes CP2, associated with the color-flavor locked symmetry spontaneously broken in the vicinity of the vortex. In this paper, we study electromagnetic coupling of the non-Abelian vortices and find that the degeneracy is removed with the induced effective potential. We obtain one stable vortex solution and a family of metastable vortex solutions, both of which carry ordinary magnetic fluxes in addition to color magnetic fluxes. We discuss quantum mechanical decay of the metastable vortices by quantum tunneling, and compare the effective potential with the other known potentials, the quantum mechanically induced potential and the potential induced by the strange quark mass.

hep-ph↗

arXiv2012

Topological classification of vortex-core structures of spin-1 Bose-Einstein condensates

We classify vortex-core structures according to the topology of the order parameter space. By developing a method to characterize how the order parameter changes inside the vortex core. We apply this method to the spin-1 Bose-Einstein condensates and show that the vortex-core structures are classified by winding numbers that are locally defined in the core region. We also show that a vortex-core structure with a nontrivial winding number can be stabilized under a negative quadratic Zeeman effect.

cond-mat.quant-gas↗