arXiv subjects

Minoru Eto

Publications and source records attributed to Minoru Eto.

At least 55 records · Page 3Linked to original sources

arXiv2019

Berezinskii-Kosterlitz-Thouless transition of two-component Bose mixtures with inter-component Josephson coupling

We study the Berezinskii-Kosterlitz-Thouless (BKT) transition of two-component Bose mixtures in two spatial dimensions. When phases of both components are decoupled, half-quantized vortex-antivortex pairs of each component induce two-step BKT transitions. On the other hand, when phases of the both components are synchronized through the inter-component Josephson coupling, two species of vortices of each component are bind to form a molecule, and in this case, we find that there is only one BKT transition by molecule-antimolecule pairs. Our results can be tested by two weakly-connected Bose systems such as two-component ultracold dilute Bose mixtures with the Rabi oscillation, and multiband superconductors.

cond-mat.stat-mech↗

arXiv2019

Massless bosons on domain walls: Jackiw-Rebbi-like mechanism for bosonic fields

It is important to obtain (nearly) massless localized modes for the low-energy four-dimensional effective field theory in the brane-world scenario. We propose a mechanism for bosonic zero modes using the field-dependent kinetic function in the classical field theory set-up. As a particularly simple case, we consider a domain wall in five dimensions, and show that massless states for scalar (0-form), vector (1-form), and tensor (2-form) fields appear on a domain wall, which may be called topological because of robustness of their existence (insensitive to continuous deformations of parameters). The spin of localized massless bosons is selected by the shape of the nonlinear kinetic function, analogously to the chirality selection of fermion by the well-known Jackiw-Rebbi mechanism. Several explicitly solvable examples are given. We consider not only (anti)BPS domain walls in non-compact extra dimension but also non-BPS domain walls in compact extra dimension.

hep-th↗

arXiv2019

Localization of gauge bosons and the Higgs mechanism on topological solitons in higher dimensions

We provide complete and self-contained formulas about localization of massless/massive Abelian gauge fields on topological solitons in generic $D$ dimensions via a field dependent gauge kinetic term. The localization takes place when a stabilizer (a scalar field) is condensed in the topological soliton. We show that the localized gauge bosons are massless when the stabilizer is neutral. On the other hand, they become massive for the charged stabilizer as a consequence of interplay between the localization mechanism and the Higgs mechanism. For concreteness, we give two examples in six dimensions. The one is domain wall intersections and the other is an axially symmetric soliton background.

hep-th↗

arXiv2018

Constraints on two Higgs doublet models from domain walls

We show that there is a constraint on the parameter space of two Higgs doublet models that comes from the existence of the stable vortex-domain wall systems. The constraint is quite universal in the sense that it depends on only two combinations of Lagrangian parameters and does not depend on how fermions couple to two Higgs fields. Numerical solutions of field configurations of domain wall-vortex system are obtained, which provide a basis for further quantitative study of cosmology which involve such topological objects.

hep-ph↗

arXiv2018

Non-Abelian strings and domain walls in two Higgs doublet models

Contrary to the standard model that does not admit topologically nontrivial solitons, two Higgs doublet models admit topologically stable vortex strings and domain walls. We numerically confirm the existence of a topological $Z$-string confining fractional $Z$-flux inside. We show that topological strings at $\sinθ_W = 0$ limit reduce to non-Abelian strings which possess non-Abelian moduli $S^2$ associated with spontaneous breakdown of the $SU(2)$ custodial symmetry. We numerically solve the equations of motion for various parameter choices. It is found that a gauging $U(1)_Y$ always lowers the tension of the $Z$-string while it keeps that of the $W$-string. On the other hand, a deformation of the Higgs potential is either raising or lowering the tensions of the $Z$-string and $W$-string. We numerically obtain an effective potential for the non-Abelian moduli $S^2$ for various parameter deformations under the restriction $\tanβ=1$. It is the first time to show that there exists a certain parameter region where the topological $W$-string can be the most stable topological excitation, contrary to conventional wisdom of electroweak theories. We also obtain numerical solutions of composites of the string and domain walls in a certain condition.

hep-ph↗

arXiv2018

Localization of the Standard Model via Higgs mechanism and a finite electroweak monopole from non-compact five dimensions

We propose a minimal and self-contained model in non-compact flat five dimensions which localizes the Standard Model (SM) on a domain wall. Localization of gauge fields is achieved by the condensation of Higgs field via a Higgs dependent gauge kinetic term in five-dimensional Lagrangian. The domain wall connecting vacua with unbroken gauge symmetry drives the Higgs condensation which provides both electroweak symmetry breaking and gauge field localization at the same time. Our model predicts higher-dimensional interactions $|H|^{2n}(F_{μν})^2$ in the low-energy effective theory. This leads to two expectations: The one is a new tree-level contribution to $H \to γγ$ ($H \to gg$) decay whose signature is testable in future LHC experiment. The other is a finite electroweak monopole which may be accessible to the MoEDAL experiment. Interactions of translational Nambu-Goldstone boson is shown to satisfy a low-energy theorem.

hep-ph↗

arXiv2018

Domain Wall and Three Dimensional Duality

We discuss 1/2 BPS domain walls in the 3d $\mathcal N=4$ supersymmetric gauge theory which is self-dual under the 3d mirror symmetry. We find that if a BF-type coupling is introduced, invariance of the BPS domain wall under the duality transformation can be explicitly seen from the classical BPS equations. It has been known that particles and vortices are swapped under the 3d duality transformations. We show that Noether charges and vortex topological charges localized on the domain walls are correctly exchanged under the 3d mirror symmetry.

hep-th↗

arXiv2018

Localized non-Abelian gauge fields in non-compact extra-dimensions

Dynamical localization of non-Abelian gauge fields in non-compact flat $D$ dimensions is worked out. The localization takes place via a field-dependent gauge kinetic term when a field condenses in a finite region of spacetime. Such a situation typically arises in the presence of topological solitons. We construct four-dimensional low-energy effective Lagrangian up to the quadratic order in a universal manner applicable to any spacetime dimensions. We devise an extension of the $R_ξ$ gauge to separate physical and unphysical modes clearly. Out of the D-dimensional non-Abelian gauge fields, the physical massless modes reside only in the four-dimensional components, whereas they are absent in the extra-dimensional components. The universality of non-Abelian gauge charges holds due to the unbroken four-dimensional gauge invariance. We illustrate our methods with models in $D=5$ (domain walls), in $D=6$ (vortices), and in $D=7$.

hep-th↗

arXiv2017

Grand Unified Brane World Scenario

We present a field theoretical model unifying grand unified theory (GUT) and brane world scenario. As a concrete example, we consider $SU(5)$ GUT in 4+1 dimensions where our 3+1 dimensional spacetime spontaneously arises on five domain walls. A field-dependent gauge kinetic term is used to localize massless non-Abelian gauge fields on the domain walls and to assure the charge universality of matter fields. We find the domain walls with the symmetry breaking $SU(5)\to SU(3)\times SU(2)\times U(1)$ as a global minimum and all the undesirable moduli are stabilized with the mass scale of $M_{\rm GUT}$. Profiles of massless Standard Model particles are determined as a consequence of wall dynamics. The proton decay can be exponentially suppressed.

hep-th↗

arXiv2017

Non-Abelian Gauge Field Localization on Walls and Geometric Higgs Mechanism

Combining the semi-classical localization mechanism for gauge fields with $N$ domain wall background in a simple $SU(N)$ gauge theory in five space-time dimensions we investigate the geometric Higgs mechanism, where a spontaneous breakdown of the gauge symmetry comes from splitting of domain walls. The mass spectra are investigated in detail for the phenomenologically interesting case $SU(5) \to SU(3)\times SU(2)\times U(1)$ which is realized on a split configuration of coincident triplet and doublet of domain walls. We derive a low energy effective theory in a generic background using the moduli approximation, where all non-linear interactions between effective fields are captured up to two derivatives. We observe novel similarities between domain walls in our model and D-branes in superstring theories.

hep-th↗

arXiv2017

Confinement of Half-quantized Vortices in Coherently Coupled Bose-Einstein Condensates: Simulating Quark Confinement in QCD

We demonstrate that the confinement of half-quantized vortices (HQVs) in coherently coupled Bose-Einstein condensates (BECs) simulates certain aspects of the confinement in $SU(2)$ quantum chromodynamics (QCD) in 2+1 space-time dimensions. By identifying the circulation of superfluid velocity as the baryon number and the relative phase between two components as a dual gluon, we identify HQVs in a single component as electrically charged particles with a half baryon number. Further, we show that only singlet states of the relative phase of two components can stably exist as bound states of vortices, that is, a pair of vortices in each component (a baryon) and a pair of a vortex and an antivortex in the same component (a meson). We then study the dynamics of a baryon and meson; baryon is static at the equilibrium and rotates once it deviates from the equilibrium, while a meson moves with constant velocity. For both baryon and meson we verify a linear confinement and determine that they are broken, thus creating other baryons or mesons in the middle when two constituent vortices are separated by more than some critical distance, resembling QCD.

cond-mat.quant-gas↗

arXiv2016

BPS Boojums in N=2 supersymmetric gauge theories I

We study 1/4 Bogomol'nyi-Prasad-Sommerfield (BPS) composite solitons of vortex strings, domain walls and boojums in ${\cal N}=2$ supersymmetric Abelian gauge theories in four dimensions. We obtain solutions to the 1/4 BPS equations with the finite gauge coupling constant. To obtain numerical solutions for generic coupling constants, we construct globally correct approximate functions which allow us to easily find fixed points of gradient flow equations. We analytically/numerically confirm that the negative mass of a single boojum appearingat the endpoint of the vortex string on the logarithmically bent domain wall is equal to the half-mass of the 't Hooft-Polyakov monopole. We examine various configurations and clarify how the shape of the boojum depends on the coupling constants and moduli parameters. We also find analytic solutions to the 1/4 BPS equations for specific values of the coupling constants.

hep-th↗

arXiv2016

BPS Boojums in N=2 supersymmetric gauge theories II

We continue our study of 1/4 Bogomol'nyi-Prasad-Sommerfield (BPS) composite solitons of vortex strings, domain walls and boojums in N=2 supersymmetric Abelian gauge theories in four dimensions. In this work, we numerically confirm that a boojum appearing at an end point of a string on a thick domain wall behaves as a magnetic monopole with a fractional charge in three dimensions. We introduce a "magnetic" scalar potential whose gradient gives magnetic fields. Height of the magnetic potential has a geometrical meaning that is shape of the domain wall. We find a semi-local extension of boojum which has an additional size moduli at an end point of a semi-local string on the domain wall. Dyonic solutions are also studied and we numerically confirm that the dyonic domain wall becomes an electric capacitor storing opposite electric charges on its skins. At the same time, the boojum becomes fractional dyon whose charge density is proportional to ${\vec E} \cdot {\vec B}$. We also study dual configurations with an infinite number of boojums and anti-boojums on parallel lines and analyze the ability of domain walls to store magnetic charge as magnetic capacitors. In understanding these phenomena, the magnetic scalar potential plays an important role. We study the composite solitons from the viewpoints of the Nambu-Goto and Dirac-Born-Infeld actions, and find the semi-local BIon as the counterpart of the semi-local Boojum.

hep-th↗

arXiv2016

Head butting sheep: Kink Collisions in the Presence of False Vacua

We investigate numerically kink collisions in a $1+1$ dimensional scalar field theory with multiple vacua. The domain wall model we are interested in involves two scalar fields and a potential term built from an asymmetric double well and (double) sine-Gordon potential together with an interaction term. Depending on the initial kink setup and impact velocities, the model allows for a wide range of scattering behaviours. Kinks can repel each other, annihilate, form true or false domain walls and reflect off each other.

hep-th↗

arXiv2016

Stabilizing semilocal strings by polarization

Semilocal strings are vortices in the extended Abelian-Higgs model with two complex Higgs scalar fields among which a global $SU(2)$ symmetry acts. They are known to be stable (unstable against expansion) in type-I (II) superconductors, in which gauge field is heavier (lighter) than the Higgs scalar field. In this paper, we find that vortices can be stabilized in the whole parameter region including the type-II region by adding a potential term breaking the $SU(2)$ symmetry. We construct numerical solutions in various parameters and determine the vortex phase diagram consisting of six phases. In two phases, a vortex is polarized, that is, split into two half-quantized vortices with a certain distance, to form a vortex molecule, while in the rests a vortex is identical to the conventional Abrikosov-Nielsen-Olesen vortex.

hep-th↗

arXiv2016

Semilocal Fractional Instantons

We find semi-local fractional instantons of codimension four in Abelian and non-Abelian gauge theories coupled with scalar fields and the corresponding ${\mathbb C}P^{N-1}$ and Grassmann sigma models at strong gauge coupling. They are 1/4 BPS states in supersymmetric theories with eight supercharges, carry fractional (half) instanton charges characterized by the fourth homotopy group $π_4 (G/H)$, and have divergent energy in infinite spaces. We construct exact solutions for the sigma models and numerical solutions for the gauge theories. Small instanton singularity in sigma models is resolved at finite gauge coupling (for the Abelian gauge theory). Instantons in Abelian and non-Abelian gauge theories have negative and positive instantons charges, respectively, which are related by the Seiberg-like duality that changes the sign of the instanton charge.

hep-th↗

arXiv2015

Short range inter-vortex interaction and interacting dynamics of half-quantized vortices in two-component Bose-Einstein condensates

We study the interaction and dynamics of two half-quantized vortices in two-component Bose- Einstein condensates. Using the Pade approximation for the vortex core profile, we calculate the intervortex potential, whose asymptotic form for a large distance has been derived by Eto et al. [Phys. Rev. A, 83, 063603 (2011)]. Through numerical simulations of the two-dimensional Gross-Pitaevskii equations, we reveal different kinds of dynamical trajectories of the vortices depending on the combinations of signs of circulations and the intercomponent density coupling. Under the adiabatic limit, we derive the equations of motion for the vortex coordinates, in which the motion is caused by the balance between Magnus force and the intervortex forces. The initial velocity of the vortex motion can be explained quantitatively by this point vortex approximation, but under- standing the long-time behavior of the dynamics needs more consideration beyond our model.

cond-mat.quant-gas↗

arXiv2015

Speed limit in internal space of domain walls via all-order effective action of moduli motion

We find that motion in internal moduli spaces of generic domain walls has an upper bound for its velocity. Our finding is based on our generic formula for all-order effective actions of internal moduli parameter of domain wall solitons. It is known that the Nambu-Goldstone mode $Z$ associated with spontaneous breaking of translation symmetry obeys a Nambu-Goto effective Lagrangian $\sqrt{1 - (\partial_0 Z)^2}$ detecting the speed of light ($|\partial_0 Z|=1$) in the target spacetime. Solitons can have internal moduli parameters as well, associated with a breaking of internal symmetries such as a phase rotation acting on a field. We obtain, for generic domain walls, an effective Lagrangian of the internal moduli $ε$ to all order in $(\partial ε)$. The Lagrangian is given by a function of the Nambu-Goto Lagrangian: $L = g(\sqrt{1 + (\partial_με)^2})$. This shows generically the existence of an upper bound on $\partial_0 ε$, i.e. a speed limit in the internal space. The speed limit exists even for solitons in some non-relativistic field theories, where we find that $ε$ is a type I Nambu-Goldstone mode which also obeys a nonlinear dispersion to reach the speed limit. This offers a possibility of detecting the speed limit in condensed matter experiments.

hep-th↗