Magnetic Bag Research Articles

Cold and dense perturbative QCD in a very strong magnetic background

We compute the pressure from first principles within perturbative QCD at finite baryon density and very high magnetic fields up to two-loops and with physical quark masses. The region of validity for our framework is given by ms≪μq≪eB, where ms is the strange quark mass, μq is the quark chemical potential, e is the fundamental electric charge, and B is the magnetic field strength. We include the effects of the renormalization scale in the running coupling, αs(μq,eB), and running strange quark mass. We also discuss the simplifications that come about in the chiral limit. The effectively negligible contribution of the exchange diagram allows for building a simple analytic model for the equation of state for pure quark magnetars and computing their mass and radius at very large values of B. These results provide constraints on the behavior of the maximum mass and associated radius from perturbative QCD. We also discuss the magnetic bag model for extreme magnetic fields. Published by the American Physical Society 2024

Vortices and magnetic bags in Abelian models with extended scalar sectors and some of their applications

A detailed study of vortices is presented in Ginzburg-Landau (or Abelian Higgs) models with two complex scalars (order parameters) assuming a general U(1)$\times$U(1) symmetric potential. Particular emphasis is given to the case, when only one of the scalars obtains a vacuum expectation value (VEV). It is found that for a significantly large domain in parameter space vortices with a scalar field condensate in their core (condensate core, CC) coexist with Abrikosov-Nielsen-Olesen (ANO) vortices. Importantly CC vortices are stable and have lower energy than the ANO ones. Magnetic bags or giant vortices of the order of 1000 flux quanta are favoured to form for the range of parameters ("strong couplings") appearing for the superconducting state of liquid metallic hydrogen (LMH). Furthermore, it is argued that finite energy/unit length 1VEV vortices are smoothly connected to fractional flux 2VEV ones. Stable, finite energy CC-type vortices are also exhibited in the case when one of the scalar fields is neutral.

Magnetic bags in hyperbolic space

A magnetic bag is an abelian approximation to a large number of coincident SU(2) BPS monopoles. In this paper we consider magnetic bags in hyperbolic space and derive their Nahm transform from the large charge limit of the discrete Nahm equation for hyperbolic monopoles. An advantage of studying magnetic bags in hyperbolic space, rather than Euclidean space, is that a range of exact charge N hyperbolic monopoles can be constructed, for arbitrarily large values of N, and compared with the magnetic bag approximation. We show that a particular magnetic bag (the magnetic disc) provides a good description of the axially symmetric N-monopole. However, an abelian magnetic bag is not a good approximation to a roughly spherical N-monopole that has more than N zeros of the Higgs field. We introduce an extension of the magnetic bag that does provide a good approximation to such monopoles and involves a spherical non-abelian interior for the bag, in addition to the conventional abelian exterior.

Magnetic Bag Like Solutions to the SU(2) Monopole Equations on $${{\mathbb R}^{3}}$$ R 3

Solutions to the SU(2) monopole equations in the Bogolmony limit are constructed that look very much like Bolognesis conjectured magnetic bag solutions. Three theorems are also stated and proved that give bounds in terms of the topological charge for the radii of balls where the solutions Higgs field has very small norm.

Magnetic domains

Recently a Nahm transform has been discovered for magnetic bags, which are conjectured to arise in the large n limit of magnetic monopoles with charge n. We interpret these ideas using string theory and present some partial proofs of this conjecture. We then extend the notion of bags and their Nahm transform to higher gauge theories and arbitrary domains. Bags in four dimensions conjecturally describe the large n limit of n self-dual strings. We show that the corresponding Basu-Harvey equation is the large n limit of an equation describing n M2-branes, and that it has a natural interpretation in loop space. We also formulate our Nahm equations using strong homotopy Lie algebras.

Hyperbolic vortices with large magnetic flux

There has been some recent interest in the study of non-abelian BPS monopoles in the limit of large magnetic charge. Most investigations have used a magnetic bag approximation, in which spherical symmetry is assumed within an abelian description. In particular, this approach has been used to suggest the existence of two types of magnetic bag, with differing distributions of the zeros of the Higgs field, together with multi-layer structures, containing several magnetic bags. This paper is concerned with the analogous situation of abelian BPS vortices in the hyperbolic plane, in the limit of large magnetic flux. This system has the advantage that explicit exact solutions can be obtained and compared with a magnetic bag approximation. Exact BPS vortex solutions are presented that are analogous to the two types of magnetic bags predicted for BPS monopoles and it is shown that these structures can be combined to produce exact multi-layer solutions.

Monopole planets and galaxies

Spherical clusters of SU(2) BPS monopoles are investigated here. A large class of monopole solutions is found using an abelian approximation, where the clusters are spherically symmetric, although exact solutions cannot have this symmetry precisely. Monopole clusters generalise the Bolognesi magnetic bag solution of the same charge, but they are always larger. Selected density profiles give structures analogous to planets of uniform density, and galaxies with a density decaying as the inverse square of the distance from the centre. The Bolognesi bag itself has features analogous to a black hole, and this analogy between monopole clusters and astrophysical objects with or without black holes in their central region is developed further. It is also shown that certain exact, platonic monopoles of small charge have sizes and other features consistent with what is expected for magnetic bags.

The Large N Limit of the Nahm Transform

We consider the large N limit of the Nahm transform, which relates charge N monopoles to solutions to the Nahm equation involving N × N matrices. In the large N limit the former approaches a magnetic bag, and the latter approaches a solution of the Nahm equation based on the Lie algebra of area-preserving vector fields on the 2-sphere. We show that the Nahm transform simplifies drastically in this limit.

Monopoles in AdS

Applications to holographic theories have led to some recent interest in magnetic monopoles in four-dimensional Anti-de Sitter spacetime. This paper is concerned with a study of these monopoles, using both analytic and numerical methods. An approximation is introduced in which the fields of a charge N monopole are explicitly given in terms of a degree N rational map. Within this approximation, it is shown that the minimal energy monopole of charge N has the same symmetry as the minimal energy Skyrmion with baryon number N in Minkowski spacetime. Beyond charge two the minimal energy monopole has only a discrete symmetry, which is often Platonic. The rational map approximation provides an upper bound on the monopole energy and may be viewed as a smooth non-abelian refinement of the magnetic bag approximation, to which it reverts under some additional approximations. The analytic results are supported by numerical solutions obtained from simulations of the non-abelian field theory. A similar analysis is performed on the monopole wall that emerges in the large N limit, to reveal a hexagonal lattice as the minimal energy architecture.

Magnetic bags and black holes

We discuss gravitational magnetic bags, i.e., clusters of large numbers of monopoles in the presence of gravitational effects. Physics depends on the dimensionless ratio between the vev of the Higgs field at infinity and the Planck mass. We solve the equations for the gravitational bags, and study the transition from monopole to black hole. The critical coupling for this transition is v cr = π / ( 4 G ) , and it is larger than that of a single 't Hooft–Polyakov monopole. We investigate the black hole limit in detail.

Multi-monopoles and magnetic bags

By analogy with the multi-vortices, we show that also multi-monopoles become magnetic bags in the large n limit. This simplification allows us to compute the spectrum and the profile functions by requiring the minimization of the energy of the bag. We consider in detail the case of the magnetic bag in the limit of vanishing potential and we find that it saturates the Bogomol'nyi bound and there is an infinite set of different shapes of allowed bags. This is consistent with the existence of a moduli space of solutions for the BPS multi-monopoles. We discuss the string theory interpretation of our result and also the relation between the 't Hooft large n limit of certain supersymmetric gauge theories and the large n limit of multi-monopoles. We then consider multi-monopoles in the cosmological context and provide a mechanism that could lead to their production.

The 1998 Outburst of XTE J1550−564: A Model Based on Multiwavelength Observations

The 1998 September outburst of the black hole X-ray binary XTE J1550-564 was monitored at X-ray, optical, and radio wavelengths. We divide the outburst sequence into five phases and discuss their multiwavelength properties. The outburst starts with a hard X-ray spike, while the soft X-ray flux rises with a longer timescale. We suggest that the onset of the outburst is determined by an increased mass transfer rate from the companion star, but the outburst morphology is determined by the distribution of specific angular momentum in the accreting matter. The companion in XTE J1550-564 is likely to be an active magnetic star, with a surface field strong enough to influence the dynamics of mass transfer. We suggest that its magnetic field can create a magnetic bag capable of confining gas inside the Roche lobe of the primary. The impulsive rise in the hard X-rays is explained by the inflow of material with low angular momentum onto the black hole, on a free-fall timescale, when the magnetic confinement breaks down. At the same time, high angular momentum matter, transferred via ordinary Roche lobe overflow, is responsible for the formation of a disk.

Portable Magnetic Flaw Detector Equipped with a Magnetic Indicator Bag

The design of a magnetic flaw detector with a magnetic bag used as a flaw indicator is discussed. Technical parameters of the detector and those of detected flaws are given.