Showing papers on "Anomaly (physics) published in 1992"

Duality Anomaly Cancellation, Minimal String Unification and the Effective Low-Energy Lagrangian of 4-D Strings

Abstract: We present a systematic study of the constraints coming from target-space duality and the associated duality anomaly cancellations on orbifold-like 4-D strings. A prominent role is played by the modular weights of the massless fields. We present a general classification of all possible modular weights of massless fields in Abelian orbifolds. We show that the cancellation of modular anomalies strongly constrains the massless fermion content of the theory, in close analogy with the standard ABJ anomalies. We emphasize the validity of this approach not only for (2,2) orbifolds but for (0,2) models with and without Wilson lines. As an application one can show that one cannot build a ${\bf Z}_3$ or ${\bf Z}_7$ orbifold whose massless charged sector with respect to the (level one) gauge group $SU(3)\times SU(2) \times U(1)$ is that of the minimal supersymmetric standard model, since any such model would necessarily have duality anomalies. A general study of those constraints for Abelian orbifolds is presented. Duality anomalies are also related to the computation of string threshold corrections to gauge coupling constants. We present an analysis of the possible relevance of those threshold corrections to the computation of $\sin^2\theta_W$ and $\alpha_3$ for all Abelian orbifolds. Some particular {\it minimal} scenarios, namely those based on all ${\bf Z}_N$ orbifolds except ${\bf Z}_6$

The renormalization of the axial anomaly in dimensional regularization

Abstract: The prescription for the γ5 matrix within dimensional regularization in multiloop calculations is elaborated. The three-loop anomalous dimension of the singlet axial current is calculated.

Nonlinear Balance and Potential-Vorticity Thinking At Large Rossby Number

Abstract: Two rational approximations are made to the divergence, potential-vorticity, and potential-temperature equations resulting in two different nonlinear balance models. Semi-balance is similar (but not identical to) the nonlinear balance model of Lorenz. Quasi-balance is a simpler model which is equivalent to quasi-geostrophy at low Rossby number and to the barotropic model at high Rossby number. Practical solutions involving methods that work for all Rossby numbers are outlined for both models. A variety of simple initial-value problems are then solved with the aim of fortifying our insight into the behaviour of flows at large Rossby numbers. the flows associated with a potential-vorticity anomaly at very large Rossby numbers differ in significant ways from the corresponding low Rossby number results. In particular, an isolated anomaly has zero vertical radius of influence at infinite Rossby number, while the induced tangential velocity in a horizontal plane containing the anomaly decreases inversely as, rather than inversely as the square of, the radius. the effects of heating and frictional forces are approached from a point of view somewhat different from that recently expressed by Haynes and McIntyre, though the physical content is the same.

Note on discrete gauge anomalies.

Abstract: We consider the problem of gauging discrete symmetries. All valid constraints on such symmetries can be understood in the low-energy theory in terms of instantons. We note that string perturbation theory often exhibits global discrete symmetries, which are broken nonperturbatively.

A practicableγ5-scheme in dimensional regularization

Abstract: We present a new simpleγ5 regularization scheme. We discuss its use in the standard radiative correction calculations including the anomaly contributions. The new scheme features an anticommutingγ5 which leads to great simplifications in practical calculations. We carefully discuss the underlying mathematics of ourγ5-scheme which is formulated in terms of simple projection operations.

Evaluating Explanations: A Content Theory

Abstract: Contents: Explanation and Understanding. Perspective on the Theory. Anomalies and Routine Understanding. Pattern-Based Anomaly Detection. Anomaly Characterization. A Vocabulary for Anomalies. Nonmotivational Anomaly Types. Evaluating Relevance and Plausibility. Focusing on Important Factors. Conclusions and Future Directions.

More About Discrete Gauge Anomalies

Abstract: I discuss and extend several results concerning the cancellation of discrete gauge anomalies. I show how heavy fermions do not decouple in the presence of discrete gauge anomalies. As a consequence, in general, cancellation of discrete gauge anomalies cannot be described merely in terms of low energy operators involving only the light fermions. I also discuss cancellation of discrete gauge anomalies through a discrete version of the Green-Schwarz (GS) mechanism as well as the possibility of discrete gauge R-symmetries and their anomalies. Finally, some phenomenological applications are discussed. This includes symmetries guaranteeing absence of FCNC in two-Higgs models and generalized matter parities stabilizing the proton in the supersymmetric standard model. In the presence of a discrete GS mechanism or/and gauge R-symmetries, new possibilities for anomaly free such symmetries are found.

Computing the Weak Mixing Angle from Anomaly Cancellation

Abstract: I remark that the weak mixing angle in the standard model may be computed even in the absence of a grand unification symmetry. In particular, if there is an additional gauged $U(1)$ symmetry at some large scale which can be made anomaly-free only by a Green-Schwarz (GS) mechanism, this typically results in a prediction for the weak angle. In the case of the standard model one can see that the standard Peccei-Quinn symmetry may be gauged and the anomalies cancelled through a GS mechanism. Remarkably enough, cancelation of anomalies works only for the `canonical' value $sin^2\theta _W=3/8$. In the case of the supersymmetric standard model one can also find $U(1)$ currents which may be made anomaly-free through a GS but the canonical value is only obtained in the absence of any Higgs multiplet. If the analysis is extended to include $U(1)$ R-symmetries, there is a unique class of $U(1)$s which give rise to the canonical value. The R-symmetry is only anomaly-free for $sin^2\theta _W=(4N_g-3)/(10N_g-3N_D-3)$, where $N_g,N_D$ are the number of generations and Higgs pairs. The natural context in which the above scenario may naturally arise is string theory. I also emphasize other interesting possibilities offered by the GS mechanism to model-building.

Nonrelativistic field-theoretic scale anomaly.

Abstract: We construct a nonrelativistic scalar field theory with a quartic self-interaction in 2+1 dimensions as an infinite mass limit of a relativistic theory, and calculate the two-particle scattering amplitude and two-particle bound-state energy. We show that the results are the same as for quantum mechanics of two scalar particles interacting via a $\ensuremath{\delta}$-function potential. Renormalization of the theory reveals an anomalous breaking of scale symmetry. The renormalization group structure is presented and the anomaly is expressed in terms of the trace of the energy-momentum tensor.

Earth's gravitational field: Seismic tomography resolves the enigma of the Laurentian Anomaly

Abstract: We demonstrate that the negative free air gravity anomaly over Hudson Bay is not due to glacial isostatic disequilibrium but rather to the influence of large scale mantle convection.

Calculated surface-energy anomaly in the 3d metals.

Abstract: Local-spin-density theory and a Green's-function technique based on the linear muffin-tin orbitals method have been used to calculate the surface energy of the 3d metals. The theory explains the variation of the values derived from measurements of the surface tension of liquid metals including the pronounced anomaly occurring between vanadium and nickel in terms of a decrease in the d contribution caused by spin polarization.

Electric charge quantization

Abstract: It has been established experimentally for a long time that the electric charges of the observed particles appear to be quantized. An approach to understanding electric-charge quantization that can be used for gauge theories with explicit U(1) factors-such as the standard model and its variants-is pedagogically reviewed and discussed. This approach uses the allowed invariances of the Lagrangian and their associated anomaly cancellation equations. The authors demonstrate that charge may be dequantized in the three-generation standard model with massless neutrinos, because differences in family-lepton numbers are anomaly free. They also review the relevant experimental limits. Their approach too charge quantization suggests that the minimal standard model should be extended so that family-lepton number differences are explicitly broken. They briefly discuss some candidate extensions (e.g. the minimal standard model augmented by Majorana right-handed neutrinos).

Analytical on-shell QED results: 3-loop vacuum polarization, 4-loop beta-function and the muon anomaly

Abstract: We present the results of analytical calculations of the 3-loop contributions to the asymptotic photon vacuum polarization function, in the on shell scheme, and of the 4-loop contributions to the on shell QED beta-function. These are used to evaluate various 4-loop and 5-loop contributions to the muon anomaly. Our analytical contributions to (g-2)_\mu differ significantly from previous numerical results. A very recent numerical re-evaluation of 4-loop muon-anomaly contributions has yielded results much closer to ours.

Electron-phonon scattering rates in disordered metallic films below 1 K.

Abstract: We have studied thin disordered metal films at low temperatures under nonequilibrium conditions. The electron temperature was raised above the lattice temperature by applying a dc bias. The Coulomb anomaly and weak localization were used as thermometers for the electrons. We confirm that at temperatures below 1 K the electron temperatures as derived from either the Coulomb anomaly or weak localization are consistent. The electron-phonon energy relaxation rate was measured to be proportional to T 3

Topological aspects of a fermion, chiral anomaly, and Berry phase

Abstract: The relationship of the Berry phase with the topological aspects of a fermion and chiral anomaly is studied here. It is observed that this phase reflects the effect of quantum geometry when the quantization procedure of a Fermi field is considered from a classical system and may be considered as the manifestation of the multiply connected nature of quantum space‐time.

DiP256: The temperature coefficient of the relative permittivity of complex perovskites and its relation to structural transformations

Abstract: The dielectric behaviour and structure of the BaxSr1–x(Zn1/3Nb2/3)O3 (BSZN) solid solution have been investigated with the intention of understanding an anomaly which exists in the temperature coefficient of the dielectric constant (τϵ) at x ≈ 0.5. A correlation between τe and the occurrence of O-octahedra tilts has been established.

Two-dimensional Lorentz-Weyl anomaly and gravitational Chern-Simons theory

Abstract: Two-dimensional chiral fermions and bosons, more generally conformal blocks of two-dimensional conformal field theories, exhibit Weyl-, Lorentz- and mixed Lorentz-Weyl anomalies. A novel way of computing these anomalies for a system of chiral bosons of arbitrary conformal spinj is sketched. It is shown that the Lorentz- and mixed Lorentz-Weyl anomalies of these theories can be cancelled by the anomalies of a three-dimensional classical Chern-Simons action for the spin connection, expressed in terms of the dreibein field. Some tentative applications of this result to string theory are indicated.

The Chern-Simons model with boundary: A Cohomological approach

Abstract: We consider a Chern–Simons model in the Landau gauge and introduce, following Symanzik ideas, a plane boundary which modifies the propagators The BRS symmetry, restored at the classical level by a suitable choice of boundary counterterms becomes anomalous due to the lower dimensionality boundary breakings The anomaly is recognized as the central charge of an algebra of conserved chiral currents defined on the boundary itself

Instability of layered quantum liquids: 1. Local-field correction in superlattices

Abstract: For a superlattice with periodd the Singwi et al. (Phys. Rev.176, 589 (1968)) approach for the local-field correction and the static structure factor is formulated. With two approximations we reduce the resulting three-dimensional integral-equation into a one-dimensional integral-equation. For the local-field correction we present analytical results for small wave numbers and large wave numbers. An expression of Hubbard-typ is derived for the local-field correction. Explicit results for boson superlattices and electron superlattice are given. A charge-density-wave instability in a layered Bose condensate withr s>rsc∝d3/4 is discovered.r s is the small parameter of the random-phase-approximation. The charge-density-wave instability is due to a many-body anomaly (short-range correlations) in layered structures and is a general property of layered quantum liquids. We find the charge-density-wave instability in a layered electron gas forr s>rsc∝d. Double-quantum-well structures are also considered. The effects of a finite well width is calculated. The general implications of the charge-density-wave instability for microscopically layered quantum liquids are pointed out.

Chain-length distribution in a model of equilibrium polymerization.

Abstract: Using renormalization-group techniques, I derive a general scaling form of the chain-length distribution for the equilibrium-polymerization model of des Cloizeaux [J. Phys. (Paris) 36, 281 (1975)]. The result allows more freedom than was assumed in some previous work. This disproves arguments suggesting that in semidilute polymer solutions there exists a phase related to some anomaly of the zero-component field theory. The scaling function of the chain-length distribution is calculated to first order in \ensuremath{\epsilon}. It varies with the overlap of the chains and, in general, differs somewhat from a Schultz distribution. No anomaly related to the semidilute limit is found. Some rather nontrivial aspects of the result are well understood in terms of de Gennes ``blob'' concept.

Anomalies in curved spacetime at finite temperature.

Abstract: We discuss the problem of the breakdown of conformal and gauge symmetries at finite temperature in curved-spacetime background, when the changes in the background are gradual, in order to have a well-defined quantum field theory at finite temperature. We obtain the expressions for Seeley's coefficients and the heat-kernel expansion in this regime. As applications, we consider the self-interacting $\ensuremath{\lambda}{\ensuremath{\varphi}}^{4}$ and chiral Schwinger models in curved backgrounds at finite temperature.

Energy-momentum of the self-fields of a moving charge in classical electromagnetism

Abstract: The fundamental problem of the energy and momentum of the self-fields of a moving charge in the classical theory of electromagnetism has not yet been solved to full satisfaction. The widely-held belief that the energy and momentum of the electromagnetic field of a moving charge should behave as components of a 4-vector under a Lorentz transformation, is not borne out by the conventional theory. This apparent anomaly has led to extensive attempts on reinterpretations or even to suggestions for outright modifications of some basic aspects of the classical theory of electromagnetism. The author shows that such drastic steps are not actually needed and that the above mentioned belief is ill-founded. A relativistically consistent picture emerges in the conventional theory when a proper account is taken of all the energy and momentum associated with the electromagnetic phenomenon in the system.