On weaker forces than gravity

The limits on hypothetical new interactions with a range accessible to detection by laboratory and geophysical experiments are briefly reviewed, and the limits at larger distances imposed by a rich body of astronomical observations are elaborated on. The systematic deviations correlated with baryon number that have recently been unearthed from the data of Eötvös' classical experiment, can bravely but consistently be interpreted as a new force whose range is narrowly bracketed somewhere in between Mercury's distance to the sun and our distance to the moon. This hypothetical long-range interaction would be five and a half orders of magnitude weaker than gravity. The new force would make like bodies attract, and would therefore not constitute an elegant explanation of why protons have not been seen to decay.     

Faster than Hermitian quantum mechanics

Given an initial quantum state |psi(I)> and a final quantum state |psi(F)>, there exist Hamiltonians H under which |psi(I)> evolves into |psi(F)>. Consider the following quantum brachistochrone problem: subject to the constraint that the difference between the largest and smallest eigenvalues of H is held fixed, which H achieves this transformation in the least time tau? For Hermitian Hamiltonians tau has a nonzero lower bound. However, among non-Hermitian PT-symmetric Hamiltonians satisfying the same energy constraint, tau can be made arbitrarily small without violating the time-energy uncertainty principle. This is because for such Hamiltonians the path from |psi(I)> to |psi(F)> can be made short. The mechanism described here is similar to that in general relativity in which the distance between two space-time points can be made small if they are connected by a wormhole. This result may have applications in quantum computing.     

Critical points in less than two dimensions

From a study of the liquid-vapour equilibrium at low temperatures in the lattice-gas and penetrable-sphere models it is concluded that the phase transformation can occur as soon as the dimensionality of the fluid exceeds one, even if, formally, by a small, non-integral amount. A hypothetical fluid of dimensionality s only slightly greater than 1 is defined through its cluster integrals, and its thermodynamic properties are deduced. It is found that its behaviour is identical to that of a one-dimensional system for temperatures above some critical temperature T _c (with T _c →0 as s →1), while for temperatures below T _c its behaviour is that of a two-phase system of dimensionality s greater than 1.     

Krichever-Novikov algebras for more than two points

Krichever-Novikov algebras of meromorphic vector fields with more than two poles on higher genus Riemann surfaces are introduced. The structure of these algebras and their induced modules of forms of weight is studied.     

More than three decades of ISOLDE physics

The ISOLDE on-line isotope separator started its operation in an external beam from the CERN SC in 1967. Since then there has been a steady development of its technical performance and its physics programme so that ISOLDE today is a major facility at CERN. This revised version was published online in July 2006 with corrections to the Cover Date.     

Real polarizers and faster than light signaling

An imperfection of real polarizers (as opposite to ideal ones) seems to provide a method for faster than light signaling, threatening the structural stability of quantum field theory. The cause of the unphysical result is explained, and the problem of structural stability is solved.     

Massless gauge bosons other than the photon

Gauge bosons associated with unbroken gauge symmetries, under which all standard model fields are singlets, may interact with ordinary matter via higher-dimensional operators. A complete set of dimension-six operators involving a massless U(1) field, gamma('), and standard model fields is presented. The mu-->egamma(') decay, primordial nucleosynthesis, star cooling, and other phenomena set lower limits on the scale of chirality-flip operators in the 1-15 TeV range if the operators have coefficients given by the corresponding Yukawa couplings. Simple renormalizable models induce gamma(') interactions with leptons or quarks at two loops, and may provide a cold dark matter candidate.     

Nonlinear optics with less than one photon

We demonstrate suppression and enhancement of spontaneous parametric down-conversion via quantum interference with two weak fields from a local oscillator (LO). Effectively, pairs of LO photons up-convert with high efficiency for appropriate phase settings, exhibiting an effective nonlinearity enhanced by at least 10 orders of magnitude. This constitutes a two-photon switch and promises to be applicable to a wide variety of quantum nonlinear optical phenomena.     

How to do better·than Brueckner-Hartree-Fock

A triple self-consistent Faddeev-Brueckner-Hartree-Fock method is shortly introduced. Its superiority over other self-consistent approaches is sketched.¹⁶O and⁴He are calculated in FBHF scheme with available realistic forces. It is suggested that two-body forces themselves cannot account for all structure effects satisfactorily.     

Massless spinors in more than four dimensions

We consider fermions in theories of higher dimensional gravity where the four-dimensional gauge group is embedded in the invariance group of d dimensional (d>4) Lorentz and general co-ordinate transformations. It is a necessary condition for obtaining massless chiral fermions from dimensional reduction that the d dimensional spinor does not admit a mass term consistent with Lorentz and general co-ordinate transformations. This is the case for a Weyl spinor for d = 6 8 mod 8, a Majorana spinor for d = 9 mod 8 or a Majorana-Weyl spinor for d = 2 mod 8.     

An axiomatic scheme more general than quantum theory

An axiomatic scheme generalizing the operational approach to quantum theory is described. Only quite general axioms ensuring the existence of well-behaved probabilities are postulated. The space-time location of macroscopic apparatus interacting with the object is explicitly taken into consideration. The states and observables are defined and their time development is considered. The classification of physical processes with respect to their reversibility or irreversibility in time is given. The conditions of Lorentz and translational invariance are formulated. Linear transformations corresponding to operations on the object are introduced. In the case of reversible processes these transformations form an algebra and linear representations of the Poincaré group arise naturally. These results are, in general, invalid for irreversible processes. The position of quantum theory in the scheme described is clarified.     

Separable states are more disordered globally than locally

A remarkable feature of quantum entanglement is that an entangled state of two parties, Alice ( A) and Bob ( B), may be more disordered locally than globally. That is, S(A)>S(A,B), where S(*) is the von Neumann entropy. It is known that satisfaction of this inequality implies that a state is nonseparable. In this paper we prove the stronger result that for separable states the vector of eigenvalues of the density matrix of system AB is majorized by the vector of eigenvalues of the density matrix of system A alone. This gives a strong sense in which a separable state is more disordered globally than locally and a new necessary condition for separability of bipartite states in arbitrary dimensions.     

Particle velocities faster than the speed of light

In connection with another article by the author, we show how it might be possible to travel faster than the speed of light. We show that for clocks and rods moving faster than the speed of light, we get instead of time dilation and Lorentz contraction, respectively, time contraction and Lorentz expansion, respectively. It is shown that this paper is in confirmation with earlier articles dealing with this subject.     

Power content M 2-values smaller than one

The M ² beam propagation factor or times-diffraction-factor is widely used to characterize the quality of laser radiation and its propagation. When M ² is defined by the normalized product of the second moments, it is easily to prove that, for each radiation field in the paraxial approach, M ²≥1, with the equality in the case of the fundamental mode. For many applications, it is more convenient to use the power content values, also proposed by ISO. They are defined as the radii of the circles which contain a certain amount of the total power, normally η=86.5%. For the corresponding power content M _pc ² , it is often assumed that its minimum is again obtained for the fundamental mode, but no proof exists. In this paper it is shown that fields can be generated with M _pc ² <1 and that it strongly depends on the power content η. One example is the superposition of two coherent Gauss–Laguerre modes with radial symmetry. The beam radius as a function of the propagation distance is calculated, and for the 86.5% power content, the value M _pc ² =0.95 is obtained. This does not mean that such a beam is of higher quality than the fundamental mode but rather that the M _pc ² is not a reliable parameter for beam characterization.     

More Events than expected from the Standard Model

Deep inelastic electron-proton scattering measurements at the DESY accelerator HERA in a previously unexplored kinematic region.DESY Information