arXiv subjects

Michael McNeil Forbes

Publications and source records attributed to Michael McNeil Forbes.

43 records · Page 3Linked to original sources

arXiv2006

Kaon Condensation in a Nambu--Jona-Lasinio (NJL) Model at High Density

We demonstrate a fully self-consistent microscopic realization of a kaon-condensed colour-flavour locked state (CFLK0) within the context of a mean-field NJL model at high density. The properties of this state are shown to be consistent with the QCD low-energy effective theory once the proper gauge neutrality conditions are satisfied, and a simple matching procedure is used to compute the pion decay constant, which agrees with the perturbative QCD result. The NJL model is used to compare the energies of the CFLK0 state to the parity even CFL state, and to determine locations of the metal/insulator transition to a phase with gapless fermionic excitations in the presence of a non-zero hypercharge chemical potential and a non-zero strange quark mass. The transition points are compared with results derived previously via effective theories and with partially self-consistent NJL calculations. We find that the qualitative physics does not change, but that the transitions are slightly lower.

hep-ph↗

arXiv2005

Stability Criteria for Breached Pair Superfluidity

We present simple, concrete, two-fermion models that exhibit thermodynamically stable isotropic translationally-invariant gapless superfluid states (breached pair superfluidity). The mass ratio between the components and the momentum structure of the interaction are crucial for determining the stability of such states: Idealized, momentum-independent (``contact'') interactions are insufficient.

hep-ph↗

arXiv2001

Domain Walls in QCD

QCD was shown to have a nontrivial vacuum structure due to the topology of the theta = theta+2*pi*n parameter. As a result of this nontrivial topology, in the large N_c limit, quasi-stable QCD domain walls appear, characterized by a transition in the singlet eta' field. We discuss the physics of these QCD domain walls as well as related axion domain walls and we present a new type of axion wall which also contains an eta' transition. We argue that these domain walls are topologically stable in the limit N_c->infinity and classically stable for large but finite N_c, however, they can decay through a tunneling process. We argue that the qualitative features of these QCD domain walls -- namely their classical stability -- persist to the realistic case of N_c=3 and that it is at least possible that their lifetime could be macroscopically large. If it is, then QCD domain walls could play an important role in the evolution of early universe and may be detectable in energetic collisions such as those at the Relativistic Heavy Ion Collider (RHIC).

hep-ph↗

arXiv2001

Global Strings in High Density QCD

We show that several types of global strings occur in colour superconducting quark matter due to the spontaneous violation of relevant U(1) symmetries. These include the baryon U(1)_B, and approximate axial U(1)_A symmetries as well as an approximate U(1)_S arising from kaon condensation. We discuss some general properties of these strings and their interactions. In particular, we demonstrate that the U(1)_A strings behave as superconducting strings. We draw some parallels between these strings and global cosmological strings and discuss some possible implications of these strings to the physics in neutron star cores.

hep-ph↗

arXiv2001

Primordial Galactic Magnetic Fields: An Application of QCD Domain Walls

We present a mechanism for generating primordial magnetic fields with large correlation lengths on the order of 100 kpc today. The mechanism is based on recently conjectured QCD domain walls or similar CP violating domain walls with QCD scale structure. Such domain walls align the electric and magnetic dipole moments of the nucleons shortly after the QCD phase transition, producing electromagnetic fields correlated along the domain walls. Through the Kibble mechanism, the domain walls attain Hubble-scale correlations which they transfer to the aligned electromagnetic fields. Due to the CP violation, the Hubble-scale walls produce helical (non-zero Chern-Simons) magnetohydrodynamic turbulence which then undergoes an inverse cascade, allowing the correlation lengths to grow to 100 kpc today. We present an estimate the magnitude of the generated electromagnetic fields in terms of the QCD parameters. We also discuss some other unexplained astrophysical phenomena which may be related to this mechanism. In particular, we discuss the relation between primordial magnetic fields and the Greisen-Zatsepin-Kuzmin (GZK) cutoff violations. We also outline how, by creating inhomogeneities in the nucleon density, QCD domain walls may lead to inhomogeneous big bang nucleosynthesis (IBBN) explaining the Omega_B excess recently measured through cosmic microwave background (CMB) distortions.

hep-ph↗

arXiv2001

Primordial galactic magnetic fields from domain walls at the QCD phase transition

We propose a mechanism to generate large-scale magnetic fields with correlation lengths of 100 kpc. Domain walls with QCD scale internal structure form and coalesce obtaining Hubble scale correlations and align nucleon spins. Due to strong CP violation, nucleons in these walls have anomalous electric and magnetic dipole moments and thus the walls are ferromagnetic. This induces electromagnetic fields with Hubble size correlations. The same CP violation also induces a maximal helicity (Chern-Simons) correlated through the Hubble volume which supports an inverse cascade allowing the initial correlations to grow to 100 kpc today. We estimate the generated electromagnetic fields in terms of the QCD parameters and discuss the effects of the resulting fields.

hep-ph↗

arXiv2000

Primordial Galactic Magnetic Fields from the QCD Phase Transition

In this paper, we propose a mechanism to generate large-scale magnetic fields with correlations lengths of 100 kpc. Domain walls with QCD scale internal structure form and coalesce obtaining Hubble size correlations and align nucleon spins. Due to strong CP violation, nucleons in these walls have anomalous electric and magnetic dipole moments and thus the walls are ferromagnetic. This induces electromagnetic fields with Hubble size correlations. The same CP violation also induces maximal helicity (Chern-Simons) correlated through the Hubble volume which supports an "inverse cascade" allowing the initial correlations to grow to 100 kpc today. We estimate the generated electromagnetic fields in terms of the QCD parameters and discuss the effects of the resulting fields.

hep-ph↗