arXiv subjects

Chandrasekhar Chatterjee

Publications and source records attributed to Chandrasekhar Chatterjee.

At least 19 recordsLinked to original sources

arXiv2020

Chemical bonds of two vortex species with a generalized Josephson term and arbitrary charges

We consider the Abelian-Higgs model with two complex scalar fields and arbitrary positive integer charges with the addition of a higher-order generalization of the Josephson term. The theory possesses vortices of both local and global variants. The only finite-energy configurations are shown to be the local vortices for which a certain combination of vortex numbers and electric charges -- called the global vortex number -- vanishes. The local vortices have rational fractional magnetic flux, as opposed to the global counterparts that can have an arbitrary fractional flux. The global vortices have angular domain walls, which we find good analytic approximate solutions for. Finally, we find a full classification of the minimal local vortices as well as a few nonminimal networks of vortices, using numerical methods.

hep-th↗

arXiv2020

Topological defects at the boundary of neutron $^{3}P_{2}$ superfluids in neutron stars

We study surface effects of neutron $^{3}P_{2}$ superfluids in neutron stars. $^{3}P_{2}$ superfluids are in uniaxial nematic (UN), D$_{2}$ biaxial nematic (BN), or D$_{4}$ BN phase, depending on the strength of magnetic fields from small to large. We suppose a neutron $^{3}P_{2}$ superfluid in a ball with a spherical boundary. Adopting a suitable boundary condition for $^{3}P_{2}$ condensates, we solve the Ginzburg-Landau equation to find several surface properties for the neutron $^{3}P_{2}$ superfluid. First, the phase on the surface can be different from that of the bulk, and symmetry restoration or breaking occurs in general on the surface. Second, the distribution of the surface energy density has an anisotropy depending on the polar angle in the sphere, which may lead to the deformation of the geometrical shape of the surface. Third, the order parameter manifold induced on the surface, which is described by two-dimensional vector fields induced on the surface from the condensates, allows topological defects (vortices) on the surface, and there must exist such defects even in the ground state thanks to the Poincaré-Hopf theorem: although the numbers of the vortices and antivortices depend on the bulk phases, the difference between them is topologically invariant (the Euler number $χ=2$) irrespective of the bulk phases. These vortices, which are not extended to the bulk, are called boojums in the context of liquid crystals and helium-3 superfluids. The surface properties of the neutron $^{3}P_{2}$ superfluid found in this paper may provide us useful information to study neutron stars.

nucl-th↗

arXiv2020

Vortex confinement transitions in the modified Goldstone model

The modified XY model is a variation of the XY model extended by a half periodic term, exhibiting a rich phase structure. As the Goldstone model, also known as the linear O(2) model, can be obtained as a continuum and regular model for the XY model, we define the modified Goldstone model as that of the modified XY model. We construct a vortex, a soliton (domain wall), and a molecule of two half-quantized vortices connected by a soliton as regular solutions of this model. Then we investigate its phase structure in two Euclidean dimensions via the functional renormalization group formalism and full numerical simulations. We argue that the field dependence of the wave function renormalization factor plays a crucial role in the existence of the line of fixed points describing the Berezinskii-Kosterlitz-Thouless (BKT) transition, which can ultimately terminate not only at one but at two end points in the modified model. This structure confirms that a two-step phase transition of the BKT and Ising types can occur in the system. We compare our renormalization group results with full numerical simulations, which also reveal that the phase transitions show a richer scenario than expected.

cond-mat.stat-mech↗

arXiv2019

Reexamining Ginzburg-Landau theory for neutron $^3P_2$ superfluidity in neutron stars

The Ginzburg-Landau (GL) effective theory is a useful tool to study a superconductivity or superfluidity near the critical temperature, and usually the expansion up to the 4th order in terms of order parameters is sufficient for the description of the second-order phase transition. In this paper, we discuss the GL equation for the neutron $^{3}P_{2}$ superfluidity relevant for interior of neutron stars. We derive the GL expansion up to the 8th order in the condensates and find that this order is necessary for the system to have the unique ground state, unlike the ordinary cases. Starting from the $LS$ potential, which provides the dominant attraction between two neutrons at the high density, we derive the GL equation in the path-integral formalism, where the auxiliary field method and the Nambu-Gor'kov representation are used. We present the detailed description for the trace calculation necessary in the derivation of the GL equation. As numerical results, we show the phase diagram of the neutron $^{3}P_{2}$ superfluidity on the plane spanned by the temperature and magnetic field, and find that the 8th order terms lead to a first-order phase transition, whose existence was predicted in the Bogoliubov-de Gennes equation but has not been found thus far within the framework of the GL expansion up to the 6th order.The first-order phase transition will affect the interior structures inside the neutron stars.

nucl-th↗

arXiv2019

Aharonov-Bohm defects

We discuss what happens when a field receiving an Aharonov-Bohm (AB) phase develops a vacuum expectation value (VEV), with an example of an Alice string in a $U(1) \times SU(2)$ gauge theory coupled with complex triplet scalar fields. We introduce scalar fields belonging to the doublet representation of $SU(2)$, charged or chargeless under the $U(1)$ gauge symmetry, that receives an AB phase around the Alice string. When the doublet develops a VEV, the Alice string turns to a global string in the absence of the interaction depending on the relative phase between the doublet and triplet, while, in the presence of such an interaction, the Alice string is confined by a soliton or domain wall and therefore the spontaneous breaking of a spatial rotation around the string is accompanied. We call such an object induced by an AB phase as an ``AB defect'', and argue that such a phenomenon is ubiquitously appearing in various systems.

hep-th↗

arXiv2019

Phase structure of neutron $^{3}P_{2}$ superfluids in strong magnetic fields in neutron stars

We discuss the effect of a strong magnetic field on neutron $^{3}P_{2}$ superfluidity. Based on the attraction in the $^{3}P_{2}$ pair of two neutrons, we derive the Ginzburg-Landau equation in the path-integral formalism by adopting the bosonization technique and leave the next-to-leading order in the expansion of the magnetic field $B$. We determine the $(T,B)$ phase diagram with temperature $T$, comprising three phases: the uniaxial nematic (UN) phase for $B=0$, D$_{2}$-biaxial nematic (BN) and D$_{4}$-BN phases in finite $B$ and strong $B$ such as magnetars, respectively, where D$_{2}$ and D$_{4}$ are dihedral groups. We find that, compared with the leading order in the magnetic field known before, the region of the D$_{2}$-BN phase in the $(T,B)$ plane is extended by the effect of the next-to-leading-order terms of the magnetic field. We also present the thermodynamic properties, such as heat capacities and spin susceptibility, and find that the spin susceptibility exhibits anisotropies in the UN, D$_{2}$-BN, and D$_{4}$-BN phases. This information will be useful to understand the internal structures of magnetars.

nucl-th↗

arXiv2019

Effects of strong magnetic fields on neutron $^{3}P_{2}$ superfluidity with spin-orbit interactions

We discuss neutron $^{3}P_{2}$ phases in the core of neutron stars in strong magnetic field (magnetars). The neutron $^{3}P_{2}$ pairing provides a wide variety of condensates, such as the uniaxial nematic and (D$_{2}$ and D$_{4}$) biaxial nematic, with different symmetries stemming from the combinations of spin and momentum. Based on the spin-orbital angular momentum coupling and the spin-magnetic field coupling of the neutrons, we derive the Ginzburg-Landau equation containing higher order terms of the magnetic field. We investigate the phase diagram of the neutron $^{3}P_{2}$ superfluidity, and find that the D$_{2}$ biaxial nematic phase is extended by the higher order terms of the magnetic field. We also discuss the thermodynamic properties, the heat capacity and the spin susceptibility.

nucl-th↗

arXiv2019

Note on a solution to domain wall problem with the Lazarides-Shafi mechanism in axion dark matter models

Axion is a promising candidate of dark matter. After the Peccei-Quinn symmetry breaking, axion strings are formed and attached by domain walls when the temperature of the universe becomes comparable to the QCD scale. Such objects can cause cosmological disasters if they are long-lived. As a solution for it, the Lazarides-Shafi mechanism is often discussed through introduction of a new non-Abelian (gauge) symmetry. We study this mechanism in detail and show configuration of strings and walls. Even if Abelian axion strings with a domain wall number greater than one are formed in the early universe, each of them is split into multiple Alice axion strings due to a repulsive force between the Alice strings even without domain wall. When domain walls are formed as the universe cools down, a single Alice string can be attached by a single wall because a vacuum is connected by a non-Abelian rotation without changing energy. Even if an Abelian axion string attached by domain walls are created due to the Kibble Zurek mechanism at the chiral phase transition, such strings are also similarly split into multiple Alice strings attached by walls in the presence of the domain wall tension. Such walls do not form stable networks since they collapse by the tension of the walls, emitting axions.

hep-ph↗

arXiv2019

Quark-hadron continuity under rotation: Vortex continuity or boojum?

Quark-hadron continuity was proposed as crossover between hadronic matter and quark matter without a phase transition, based on the matching of the symmetry and excitations in both phases. In the limit of a light strange-quark mass, it connects hyperon matter and the color-flavor-locked (CFL) phase exhibiting color superconductivity. Recently, it was proposed that this conjecture could be generalized in the presence of superfluid vortices penetrating both phases (arXiv:1803.05115 [hep-ph]), and it was suggested that one hadronic superfluid vortex in hyperon matter could be connected to one non-Abelian vortex (color magnetic flux tube) in the CFL phase. Here, we argue that their proposal is consistent only at large distances; instead, we show that three hadronic superfluid vortices must combine with three non-Abelian vortices with different colors with the total color magnetic fluxes canceled out, where the junction is called a colorful boojum. We rigorously prove this in both a macroscopic theory based on the Ginzburg-Landau description in which symmetry and excitations match (including vortex cores), and a microscopic theory in which the Aharonov-Bohm phases of quarks around vortices match.

hep-ph↗

arXiv2019

Quark-Hadron Crossover with Vortices

The quark-hadron crossover conjecture was proposed as a continuity between hadronic matter and quark matter with no phase transition. It is based on matching of symmetry and excitations in both the phases. It connects hyperon matter and color-flavor locked (CFL) phase of color superconductivity in the limit of light strange quark mass. We study generalization of this conjecture in the presence of topological vortices. We propose a picture where hadronic superfluid vortices in hyperon matter could be connected to non-Abelian vortices (color magnetic flux tubes) in the CFL phase during this crossover. We propose that three hadronic superfluid vortices must join together to three non-Abelian vortices with different color fluxes with the total color magnetic fluxes canceled out, where the junction is called a colorful boojum.

hep-ph↗

arXiv2018

Topological Defects in the Georgi-Machacek Model

We study topological defects in the Georgi-Machacek model in a hierarchical symmetry breaking in which extra triplets acquire vacuum expectation values before the doublet. We find a possibility of topologically stable non-Abelian domain walls and non-Abelian flux tubes (vortices) in this model. In the limit of the vanishing $U(1)_{\rm Y}$ gauge coupling in which the custodial symmetry becomes exact, the presence of a vortex spontaneously breaks the custodial symmetry, giving rise to $S^2$ Nambu-Goldstone (NG) modes localized around the vortex corresponding to non-Abelian fluxes. Vortices are continuously degenerated by these degrees of freedom, thereby called non-Abelian. By taking into account the $U(1)_{\rm Y}$ gauge coupling, the custodial symmetry is explicitly broken, the NG modes are lifted, and all non-Abelian vortices fall into a topologically stable $Z$-string. This is in contrast to the SM in which $Z$-strings are non-topological and are unstable in the realistic parameter region.Non-Abelian domain walls also break the custodial symmetry and are accompanied by localized $S^2$ NG modes. Finally, we discuss the existence of domain wall solutions bounded by flux tubes, where their $S^2$ NG modes match. The domain walls may quantum mechanically decay by creating a hole bounded by a flux tube loop, and would be cosmologically safe. Gravitational waves produced from unstable domain walls could be detected by future experiments

hep-ph↗

arXiv2017

Collective excitations of a quantized vortex in $^3P_2$ superfluids in neutron stars

We discuss collective excitations (both fundamental and solitonic excitations) of quantized superfluid vortices in neutron $^3P_2$ superfluids, which likely exist in high density neutron matter such as neutron stars. Besides the well-known Kelvin modes (translational zero modes), we find a gapfull mode whose low-energy description takes the simple form of a double sine-Gordon model. The associated kink solution and its effects on spontaneous magnetization inside the vortex core are analyzed in detail.

nucl-th↗

arXiv2017

BPS Alice strings

When a charged particle encircles around an Alice string, it changes the sign of the electric charge. In this paper we find a BPS-saturated Alice string in $U(1)\times SO(3)$ gauge theory with charged complex scalar fields belonging to the vector representation. After performing BPS completion we solve the BPS equations numerically. We further embed the Alice string into an ${\cal N}=1$ supersymmetric gauge theory to show that it is half BPS.

hep-th↗

arXiv2017

The effective action of a BPS Alice string

Recently a BPS Alice string has been found in a $U(1)\times SU(2)$ gauge theory coupled with a charged complex adjoint scalar field arXiv:1703.08971. It is a half BPS state preserving a half of supercharges when embedded into a supersymmetric gauge theory. In this paper, we study zero modes of a BPS Alice string. After presenting $U(1)$ and translational zero modes, we construct the effective action of these modes. In contrast to previous analysis of the conventional Alice string for which only large distance behaviors are known, we can perform calculation exactly in the full space thanks to BPS properties.

hep-th↗

arXiv2017

Stable non-Abelian semi-superfluid vortices in dense QCD

Color superconductivity is expected to be formed in high density quark matter where color symmetry is spontaneously broken in the presence of di-quark condensate. Stable non-Abelian vortices or color magnetic flux tubes exist in the color-flavor locked phase at asymptotically high density. $\mathbb{C}P^2$ Nambu-Goldstone(NG) bosons and Majorana fermions belonging to the triplet representation are localized around a non-Abelian vortex. We discuss the zero mode analysis and the low-energy effective world sheet theory of a non-Abelian vortex. We determine the interactions of these bosonic and fermionic modes by using the nonlinear realization method. We also discuss the Aharanov-Bohm (AB) phases of charged particles, such as, electrons, muons, and color-flavor locked mesons made of tetra-quarks encircling around a non-Abelian vortex in the presence of electro-magnetic fields. This is a review based on our recent works arXiv:1602.01677, arXiv:1512.06603, arXiv:1612.09419.

hep-ph↗

arXiv2017

Meissner effect and a stringlike interaction

We find that a recently proposed interaction involving the vorticity current of electrons, which radiatively induces a photon mass in 3+1 dimensions in the low-energy effective theory, corresponds to confining strings (linear potential) between electrons.

hep-th↗

arXiv2017

Low-energy Effective Worldsheet theory of a non-Abelian vortex in high-density QCD Revisited: A regular gauge construction

Color symmetry is spontaneously broken in quark matter at high density as a consequence of di-quark condensations with exhibiting color superconductivity. Non-Abelian vortices or color magnetic flux tubes stably exist in the color-flavor locked phase at asymptotically high-density. The effective worldsheet theory of a single non-Abelian vortex was previously calculated in the singular gauge to obtain the ${\mathbb C}P^2$ model [ arXiv:0908.4470 , arXiv:0912.1352 ]. Here, we reconstruct the effective theory in a regular gauge without taking a singular gauge, confirming the previous results in the singular gauge. As a byproduct of our analysis, we find that non-Abelian vortices in high-density QCD do not suffer from any obstruction for the global definition of a symmetry breaking.

hep-ph↗

arXiv2016

Aharonov-Bohm Phase in High Density Quark Matter

Stable non-Abelian vortices, which are color magnetic flux tubes as well as superfluid vortices, are present in the color-flavor locked phase of dense quark matter with diquark condensations. We calculate the Aharanov-Bohm phases of charged particles, that is, electrons, muons, and color-flavor locked mesons made of tetraquarks around a non-Abelian vortex.

hep-ph↗