Search Results (27 total)

The effects of a nonvanishing value for the cosmological constant in the scenario of Lorentz symmetry breaking recently proposed by Cohen and Glashow (which they denote as very special relativity) are explored and observable consequences are pointed out.

The interaction between charged particles and the vacuum fluctuations of the electromagnetic field induces decoherence, and therefore affects the contrast of fringes in an interference experiment. In this article we show that if a double slit experiment is performed near a conducting grating, the fringe visibility is reduced. We find that the reduction of contrast is proportional to the number of grooves in the conducting surface, and that for realistic values of the parameters it could be large enough to be observed. The effect can be computed and understood in terms of the Smith-Purcell radiation produced by the surface currents induced in the conductor.

We point out a generic inconsistency of the coupling of ordinary gravity as described by general relativity with matter invariant only under unimodular diffeomorphisms, and some previously studied exceptions are pointed out. The most general Lagrangian invariant under unimodular diffeomorphism up to dimension-five operators is determined, and consistency with existing observations is studied in some cases.

Some models are presented in which the strength of the gravitational coupling of the potential energy relative to the same coupling for the kinetic energy is, in a precise sense, adjustable. The gauge symmetry of these models consists of those coordinate changes with unit Jacobian.

Several ways of computing the radiative corrections to the heavy boson masses in Kaluza-Klein theory are discussed. It is argued that only an intrinsically higher dimensional approach embodies all the desired physical properties. This contradicts earlier results in the literature.

We compute the vacuum polarization associated with quantum massless fields around stars with spherical symmetry. The nonlocal contribution to the vacuum polarization is dominant in the weak field limit and induces quantum corrections to the static exterior metric that depend on the inner structure of the star. It also violates the null energy conditions. We argue that similar results also hold in the low energy limit of quantum gravity. Previous calculations of the vacuum polarization in spherically symmetric spacetimes, based on local approximations, are not adequate for Newtonian stars.

We consider possible effects of new physics (NP) on the angular distributions of the decay B⁰→ϕK^*0, showing how these effects depend on the nature of nonstandard interactions. In a general framework based on factorization, we show that triple products can be used to probe the chirality of NP currents. In this analysis we take into account the presence of nonvanishing strong phases, which is motivated by recent experimental evidence. It is seen that the observability of right-handed NP is strongly dependent on the relation between the relative magnitude of these phases and the ratio of standard model and NP scales. As an application we estimate the expected values of relevant observables in a particular left-right symmetric model.

Several quantum proper time derivatives are obtained from the Beck one in the usual framework of relativistic quantum mechanics (spin-1/2 case). The ‘‘scalar Hamiltonians’’ of these derivatives should be thought of as the conjugate variables of the proper time. Then, the Hamiltonians would play the role of mass operators, suggesting the formulation of an adequate extended indefinite mass framework. We propose and briefly develop the framework corresponding to the Feynman parametrization of the Dirac equation. In such a case we derive the other parametrizations known in the literature, linking the extension of the different proposals of quantum proper time derivatives again.

A new arena for the dynamics of spacetime is proposed, in which the basic quantum variable is the two-point distance on a metric space. The scaling dimension (that is, the Kolmogorov capacity) in the neighborhood of each point then defines in a natural way a local concept of dimension. We study our model in the region of parameter space in which the resulting spacetime is not too different from a smooth manifold.

Using an explicit expression for the thermal soliton sector, we compute the would-be divergent terms of the free energy of heterotic strings when a nontrivial homology cycle in the Riemann surface is pinched. Modulo a plausible hypothesis, we find exactly the same critical temperature as in the lowest order. We also make some comments on the validity of our hypothesis. Our result is consistent with recent findings on the constant asymptotic form of the decay width for closed strings.

It was observed some time ago that the high-temperature limit of an even number of chiral fermions with a gauge interaction contains at finite density a Chern-Simons term. Using the fact that this term actually dominates when βμ≫1, we compute exactly the partition function in this limit, both for an ordinary gauge theory and for fermions interacting gravitationally.

We study the behavior of Wilson lines at finite temperature in the simple situation in which there are only one or two Wilson lines present, and the topology of the spacetime is R²×S¹×S¹. We find that the pattern of symmetry breaking is not affected by thermal fluctuations in this case and, in particular, the symmetry is not restored above a characteristic temperature.

Both β duality and R duality in the toroidal compactification of heterotic strings are shown to be symmetries of the contribution of arbitrary genus to the free energy. This symmetry relates physics at radius R and coupling κ with physics at radius α^′ / R and coupling κ(α^′ / R²)^{d / 2} where d is the number of dimensions compactified. Some comments on the possible breaking of duality by nonperturbative effects are also included.

This article presents a general overview of the problems involved in the application of the quantum principle to a theory of gravitation. The ultraviolet divergences that appear in any perturbative computation are reviewed in some detail, and it is argued that it is unlikely that any theory based on local quantum fields could be consistent. This leads in a natural way to a supersymmetric theory of extended objects as the next candidate theory to study. An elementary introduction to superstrings closes the review, and some speculations about the most promising avenues of research are offered.

This article presents a general overview of the problems involved in the application of the quantum principle to a theory of gravitation. The ultraviolet divergences that appear in any perturbative computation are reviewed in some detail, and it is argued that it is unlikely that any theory based on local quantum fields could be consistent. This leads in a natural way to a supersymmetric theory of extended objects as the next candidate theory to study. An elementary introduction to superstrings closes the review, and some speculations about the most promising avenues of research are offered.

The free energy of the heterotic string is computed in the one-loop approximation. Its infrared and ultraviolet behaviors are carefully analyzed, and their physical meaning is discussed. The properties of the zero-temperature limit are explored, as well as the possibility of a phase transition at a temperature of the order of the Planck mass.

Some cosmological consequences of the assumption that superstrings are more fundamental objects than ordinary local quantum fields are examined. We study, in particular, the dependence of both the string tension and the temperature of the primordial string soup on cosmic time. A particular scenario is proposed in which the universe undergoes a contracting ‘‘string phase’’ before the ordinary ‘‘big bang,’’ which according to this picture is nothing but the outcome of the transition from nonlocal to local fundamental physics.

Freund and Rubin's ansatz for the ground state of N=1 supergravity in 11 dimensions can be easily generalized by allowing a cosmological time dependence of the vacuum expectation value of the antisymmetric tensor field. Some numerical solutions of the corresponding field equations (in the classical approximation) are presented, and the resulting physical picture of the primeval universe is discussed.

It is shown that a large class of supersymmetric models in quantum mechanics with dynamical supersymmetry breaking (generalizations of the one proposed by Witten) do not have a consistent extension to local supersymmetry.

By means of a formal expansion of the partition function presumably valid at large baryon densities, the propagator of the quarks is expressed in terms of the gluon propagator. This result is interpreted as implying that correlations between quarks and gluons are unimportant at high enough density, so that a kind of mean-field approximation gives a very accurate description of the physical system.

The phenomenon of "dynamical compactification" in a universe with 4+n_c dimensions is studied, and it is found that if the whole process is adiabatic, entropy is pumped into the effective four-dimensional universe. Some cosmological consequences of this fact are discussed.

A calculation is made of the critical density ρ_t at which it is more favorable for matter to be in the quark phase than in the nuclear phase. The equation of state of the quark phase is obtained assuming that the quantumchromodynamic effective Lagrangian satisfactorily describes the interaction at all energies, and by making a relativistic Hartree-Fock approximation. The main result we get is that ρ_t>ρ_m, the maximum central density of stable neutron stars.