123163587
Improved loop expansion for the effective potential of coupled boson-fermion systems at finite temperature and density
The effective potential V(phi) of a scalar field theory coupled to fermions is undefined near phi = 0 if the scalar field has a spontaneously broken symmetry. This shows up in a loop expansion as an imaginary part in V(phi) which persists to all temperatures and densities, even when the symmetry is restored. This paper presents a modification of the loop expansion which yields a real V(phi) whenever the one-loop fermion corrections restore the symmetry.
34427103
Cosmology with an extremely light scalar field.
A theory with a vanishing cosmological constant can have a nonzero effective cosmological constant of cosmological significance if the theory has a scalar field with a mass m of the order of the inverse age of the Universe (tau/similar to/10/sup 33/ eV/sup -1/) provided the field has a nonzero but evolving expectation value. We discuss the cosmological consequences of scalar fields with masses mapprox. <10/sup -28/ eV. The effect on the age of the Universe and on the growth of density perturbations is discussed in detail. For small masses (mapprox.
122529357
Momentum boundary conditions and Euclidean field theory
The authors discuss the effect of the imposition of momentum boundary conditions on the semiclassical approximation to Euclidean path integrals. For free field theories they derive an explicit simple expression for the resulting Euclidean path integral. As an example they discuss the relationship between the formulation of a massless scalar field theory in terms of a 2-form potential which is used in the context of wormholes and its usual formulation.
120480610
Screening Solutions to Classical Yang-Mills Theory
We present two new solutions to the classical Yang-Mills field equations in the presence of a localized external source. These solutions totally screen the charge of the source. They have lower energy than the corresponding Coulomb solution.
40079538
Consistency of Hamiltonian diagonalization for field theories in a Robertson-Walker background.
6193348
How to distinguish a confining from a deconfining phase in gauge theories with fermions.
119300936
Differential rotation in fully convective stars
Under the assumption of thermal wind balance and effective entropy mixing in constant rotation surfaces, the isorotational contours of the solar convective zone may be reproduced with great fidelity. Even at this early stage of development, this helioseismology fit may be used to put a lower bound on the mid-latitude radial solar entropy gradient, which is in good accord with standard mixing length theory. In this paper, we generalize this solar calculation to fully convective stars (and potentially planets), retaining the assumptions of thermal wind balance and effective entropy mixing in isorotational surfaces. It is found that each isorotation contour is of the form R 2 = A + B� (r), where R is the radius from the rotation axis, � (r) is the (assumed spherical) gravitational potential, and A and B are constants along the contour. This result is applied to simple models of fully convective stars. Both solar-like surface rotation profiles (angular velocity decreasing toward the poles) as well as ‘antisolar’ profiles (angular velocity increasing toward the poles) are modelled; the latter bear some suggestive resemblance to numerical simulations. We also perform exploratory studies of zonal surface flows similar to those seen in Jupiter and Saturn. In addition to providing a practical framework for understanding the results of large-scale numerical simulations, our findings may also prove useful in dynamical calculations for which a simple but viable model for the background rotation profile in a convecting fluid is needed. Finally, our work bears directly on an important goal of the CoRoT programme: to elucidate the internal structure of rotating, convecting stars.
7847831
FINE STRUCTURE IN SUNSPOTS
▪ Abstract Important physical processes on the Sun, and especially in sunspots, occur on spatial scales at or below the limiting resolution of current solar telescopes. Over the past decade, using ...
16284410
Differential rotation and convection in the Sun
We show that the differential rotation profile of the solar convection zone, apart from inner and outer boundary layers, can be reproduced with great accuracy if the isorotation contours correspond to characteristics of the thermal wind equation. This requires that there be a formal quantitative relationship involving the entropy and the angular velocity. Earlier work has suggested that this could arise from magnetohydrodynamic stability constraints; here, we argue that purely hydrodynamical processes could also lead to such a result. Of special importance to the hydrodynamical solution is the fact that the thermal wind equation is insensitive to radial entropy gradients. This allows a much more general class of solutions to fit the solar isorotation contours, beyond just those in which the entropy itself must be a function of the angular velocity. In particular, for this expanded class, the thermal wind solution of the solar rotation profile remains valid even when large radial entropy gradients are present. A clear and explicit example of this class of solution appears to be present in published numerical simulations of the solar convective zone. Though hydrodynamical in character, the theory is not sensitive to the presence of weak magnetic fields. Thus, the identification of solar isorotation contours with the characteristics of the thermal wind equation appears to be robust, accommodating, but by no means requiring, magnetic field dynamics.
119105808
Global model of differential rotation in the Sun
The isorotation contours of the solar convective zone (SCZ) show three distinct morphologies, corresponding to two boundary layers (inner and outer), and the bulk of the interior. Previous work has shown that the thermal wind equation (TWE) together with informal arguments on the nature of convection in a rotating fluid could be used to deduce the shape of the isorotation surfaces in the bulk of the SCZ with great fidelity, and that the tachocline contours could also be described by relatively simple phenomenology. In this paper, we show that the form of these surfaces can be understood more broadly as a mathematical consequence of the TWE and a narrow convective shell. The analysis does not yield the angular velocity function directly; an additional surface boundary condition is required. However, much can already be deduced without constructing the entire rotation profile. The mathematics may be combined with dynamical arguments put forth in previous works to the mutual benefit of each. An important element of our approach is to regard the constant angular velocity surfaces as an independent coordinate variable for what is termed the ‘residual entropy’, a quantity that plays a key role in the equation of thermal wind balance. The difference between the dynamics of the bulk of the SCZ and the tachocline is due to a different functional form of the residual entropy in each region. We develop a unified theory for the rotational behaviour of both the SCZ and the tachocline, using the solutions for the characteristics of the TWE. These characteristics are identical to the isorotation contours in the bulk of the SCZ, but the two deviate in the tachocline. The outer layer may be treated, at least descriptively, by similar mathematical techniques, but this region probably does not obey thermal wind balance.