Causality violation in spatially closed space-times

Some results are obtained which establish conditions under which causality violation cannot occur in space-times admitting a compact, but not necessarily acausal, spacelike hypersurface. For example, it is shown that causality violation can occur in a space-time admitting a compact spacelike slice and obeying fairly reasonable energy conditions only if it is “singular” in the sense that some “causal interval”J ⁺(p) ∩J ^? (q) has noncompact closure.     

Properties of straight and curved neutron guide tubes

The properties of straight and curved neutron guides for neutrons of the energy region 4·10^?7 eV≦E≦2·10^?6 eV (very cold neutrons) are investigated. Experimental data for the angular distribution of neutrons emerging from a straight neutron guide are presented and it is shown that they can be theoretically verified using Steyerl's approximation. In the second part we consider a strongly curved neutron guide. The effect of laminating such a guide is investigated experimentally and theoretically and the conditions for optimum transmission are discussed.     

Tachyons in X-ray films deep under the lead and soil

The study of double extensive air showers (EAS) with N _e ≥ 5 · 10⁶ particles separated in time by intervals of the order of 100 ns showed (JETP Lett. 85, 101 (2007)) that to explain the origin of “delayed” showers as a result of formation in the first interaction of heavy particles, the mass of such particles must reach 5 · 10⁵ GeV. Such an explanation seems improbable. That is why it was assumed that advanced showers can be generated by tachyons. In this connection we decided to return to the analysis of our unpublished data on the anomalous events in X-ray films deep under the lead and soil. These events, we believe, can also be explained by the tachyon hypothesis.     

In search of the ηc

We argue that the X(2.88) detected in π^?p → γγ + n at 40 GeV/c cannot be the η_c. We discuss the possibility that a qq?cc? state is produced there, probably the same state discovered in radiative decay of the J/ψ. Only at much higher energies is the η_c expected to dominate over qq?cc? in the π^?p interaction. We also discuss coherent photoproduction and find that four quark state production would dominate over η_c.     

Measurement of np elastic scattering at high energies and very small momentum transfers

The np elastic differential cross section has been measured for incident neutron momenta 100–400 GeV/c in the |t| range 6 · 10^?6 ? 5 · 10^?1 (GeV/c)². The np data of this experiment provide a first direct measurement of the hadronic amplitude for |t| < 10^?2 (GeV/c)², which is consistent with the extrapolations from higher |t| values. Our data for |t| < 10^?4 (GeV/c)² are consistent with a rise which can be attributed to Schwinger scattering, caused by the interaction of the neutron magnetic moment with the proton.     

Light induced molecular magnetic polaron in EuO

Stoechiometric EuO samples do not present insulator metal transition below Curie temperature (T_c = 70 K). Experimental data presented in this paper show that when these samples are illuminated, it appears: an insulator metal transition below T_c, and, at room temperature, a decrease of activation energy, as well as a small increase in conductivity. Oxygen deficient samples exhibit usually this insulator metal transition. When they are illuminated room temperature activation energy remains unchanged, and the insulator metal transition is more important. These results cannot be explained by means of a free electron model. Electrons are photoexcitated from 4? levels, or donor levels, to conduction band. Then, these electrons polarise Eu²⁺ spins and make magnetic polarons. These polarons cannot be “Bound Magnetic Polarons” because samples do not contain oxygen vacancies. In addition these polarons would be stable until room temperature. Thus, they are expected to be “Molecular Magnetic Polarons”. Our results confirm then this model proposed by Kusuya.     

Estimation of sound velocities from resonance measurements on tungsten carbide calibration spheres

Tungsten carbide spheres have been used as reference targets to calibrate echosounders. The target strength depends upon the longitudinal and transverse stress wave speeds, c₁ and c₂, in the sphere. These may be estimated from the resonance frequencies, which can be measured precisely given two or more resonances whose coupling characteristics are sufficiently different to provide well conditioned equations for these wave speeds. The resonance frequencies may be measured by sampling the echo amplitude or by spectrum analysis. The latter method is more accurate but requires more sophisticated equipment. The measurements have been corrected to remove the bias resulting from the finite bandwidth of the apparatus. Experimental results are given for 11 spheres 38·1 mm in diameter containing a nominal 6% of cobalt binder, procured in two batches from different production runs. Both stress wave speeds are significantly different between but not within the batches, and likewise the sphere density which indicates variation of the cobalt content. For a density of 14 900 kg m^?3 (6% cobalt) and at 11°C, c₁ and c₂ are estimated to be 6853 ± 19 and 4171 ± 7 m s^?1, respectively, within 95% confidence limits. Empirical equations are presented for the speeds as functions of density. The temperature coefficient of c₂ is estimated to be ?1·3 ± 0·6 m s^?1°C^?1. These results demonstrate the high accuracy of the resonance technique for estimating the stress wave speeds in spheres. The small differences observed between the spheres would have a negligible effect on the target strength at 38 kHz.     

Investigation of the decay of charmed particles produced in neutrino interactions

The decay of charmed particles produced by high-energy neutrinos has been studied by an experiment using simultaneously emulsion, bubble chamber and counter techniques. Eight charmed particle candidates, 5 positively charged and 3 neutral, have been found in the emulsion, where their production and decay have been directly observed. One of these events is identified as a Λ_c⁺ baryon of mass 2.26±0.02 GeV/c² which undergoes the decay Λ_c⁺→pK^?π⁺ after a proper time of (7.3±0.1) · 10^?13 s.A statistical analysis of the other observed decays leads to the mean-life values τ⁺=(2.5_?1.1^+2.2) · 10^?13 s, τ⁰=(0.53_?0.25^+0.57) · 10^?13 s, for the sample of charged particles enriched by a similar event found in a previous experiment, and for the sample of 3 neutral particles, respectively. The former value is only slightly affected by including in the sample the Λ_c⁺ event or excluding that of the previous experiment.     

Quantum and classical relativistic energy states in stationary geometries

The positive and negative root states (E⁺, E^?) for a particle moving along a geodesic in a stationary background, introduced by Christodoulou and Ruffini, are here interpreted in the framework of a relativistic quantum field theory. It is shown how E⁺ and E^? have to be considered as the classical correspondent of the positive and negative energy states of a quantized field. It is explicitly shown that crossing between the states E⁺ and E^? can occur and consequently the necessary condition for particle creation as given by Klein, Sauter, Heisenberg and Euler can be encountered.     

Klein paradox in a kerr geometry

The crossing of the classical positive and negative energy states E⁺ and E^? introduced by Christodoulou-Ruffini and interpreted within the framework of a relativistic quantum field theory by Deruelle and Ruffini, leads to a Klein paradox. It has been shown by Euler and Heisenberg that when the transmission coefficient T² through the barrier between the E⁺ and E^? states is small it is proportional to the probability of pair creation. Numerical computations show that, in the case of a small Kerr black hole (GM/c² ??/muc), the probability of pair creation of particles of mass μ is maximum when $\text{E ～ ?Ω}$, where E is the energy of the created particles and Ω and M the angular velocity and the mass of the back hole.     

Mass and lifetime limits on new long-lived particles in 300 GeV/c π− interactions

A sensitive search has been done for the production of new long-lived and penetrating particles by 300 GeV/c negative pions. No new state —decaying into at least two charged known particles —has been detected with mass above 1 GeV/c² and lifetime in the range 5·10^?11 s to 5·10^?7s. We give upper limits on production cross sections, and consequences on the existence of heavy “axion-like” particles, heavy neutrinos and supersymmetric particles. In particular, this experiment excludes the existence of light gluinos with lifetime in the range 5·10^?11 to 10^?8s: this closes the last “window of opportunity” for gluinos withM<2 GeV/c² and lifetime measurable in particle physics experiments.     

Transport properties of n-type ferromagnetic semiconductor HgCr2−xInxSe4(x = 0.100)

Measurements of the electrical conductivity, magnetoresistance, and Hall effect were performed on a n-type ferromagnetic semiconductor HgCr_2?xIn_xSe₄(x = 0.100) single crystal from 6.3 to 296 K in magnetic fields up to 1.19×l0⁶A/m. The conductivity decreases rapidly near the Curie temperatureT_c (≈120 K) as the temperature is raised. A large peak in the magnetoresistance is observed near T_c. The Hall effect measurements indicate that the temperature dependence of the conductivity and the magnetoresistance are due mostly to a change in electron mobility. The electron mobility is 1.2 × 10^?2 m²/V · s at 6.3 K, and decreases rapidly near T_c with the rise in temperature. Then it increases slowly from 5.5 × 10^?4 m²/V · s at 160 K to 7.5 × 10^?4 m²/V · s at 241 K. This temperature dependence of the electron mobility can be explained in terms of the spin-disorder scattering which takes into account the exchange interaction between charge carriers and localized magnetic moments.     

Twenty-parameter eigenfunctions and energy values of the 23 S States of He and He-like Ions

Twenty-parameter calculations of the energies and wave functions of the first excited states 2³ S of He, Li⁺, Be⁺⁺, B⁺⁺⁺, O⁶⁺, Ne⁸⁺, Mg¹⁰⁺, have been carried out using Hylleraas' method. The energy values have been corrected for mass polarization. The coefficients of the best wave functions are listed. Similar calculations for the 2³ S state of the H^? ion yield an energy value which cannot be distinguished from the energy of a free H atom. For He and Li⁺, in addition, forty-parameter calculations have been carried out. The results compare well with the recent calculations of Pekeris using a somewhat different method. Even after the inclusion of the relativistic correction, the theoretical energy values deviate slightly from the observed. The differences, ?0·10±0·05 cm^?1 for He and ?1·07±0·10 cm^?1 for Li⁺, represent observed values of the Lamb shifts in the 2³ S states. These values agree within their uncertainties with the values predicted from quantum electrodynamics.     

Structure in momentum-transfer for (pπ−) systems produced in diffractive dissociation of neutrons on protons

The four-momentum transfer distribution of (pπ^?) systems produced in the neutron dissociation reaction n + p → (pπ^?) + p has substantial structure which depends strongly on the mass and on the angular decay properties of the produced (pπ^?) system. No significant energy dependence is observed in the data for incident neutrons in the momentum range between 50 GeV/c and 300 GeV/c. The results are compared with a Deck-type of model.     

Reconciling causality with superluminal travel

A tachyon or a superluminal wave group appears as a spacelike structure through a region in the reference frame in which it is at rest. Such a structure can arise from residue left (a) by a particle or wave group traveling at fundamental speed c or less, or (b) in the creation or separation of particles. Thus, Maund's argument does not prove that tachyons cannot exist. Creation may include lepton-quark production as well as particle-antiparticle production.     

Search for charginos,neutralinos and gravitinos in e+e− interactions at s=183 GeV

An update of the searches for charginos and neutralinos is presented, based on a data sample corresponding to the 53.9 pb⁻¹ recorded by the DELPHI detector in 1997, at a centre-of-mass energy of 183 GeV. No evidence for a signal was found. The lower mass limits are 4–5 GeV/c² higher than those obtained at a centre-of-mass energy of 172 GeV. The (μ,M₂) domain excluded by combining the neutralino and chargino searches implies a limit on the mass of the lightest neutralino which, for a heavy sneutrino, is constrained to be above 29.1 GeV/c² for tanβ≥ 1.     

A study of e+e− pairs in the mass range 11 to 25 GeV/c2 at the CERN intersecting storage rings

A sample of 58e⁺e^? events with an invariant mass greater than 11 GeV/c² produced in pp collisions at a centre-of-mass energy of 62.3 GeV is discussed. The cross sections are presented as a function of the mass and transverse momentum. The electron pairs produced with a mean transverse momentum of 2.50 ± 0.25 GeV/c.     

Noninversive partial velocity amplification of radiation by ions due to their rotation in a magnetic field

It is shown that upon the application of an external magnetic field, a gas of ionized particles may experience noninversive partial velocity amplification of radiation by ions due to their Larmor rotation. In this case, virtually all ions may be in the ground state. It may happen that approximately half the number of ions in the medium amplify the incident radiation. The integrated absorption coefficient remains positive due to the enhancement of absorption of radiation by the other half of ions. Noninversive amplification of radiation takes place when the condition ω_c?Γ²/kv _T is satisfied ωw_c is the cyclotron frequency of ions in the magnetic field; Γ is the homogeneous half-width of the absorption line for ions, and kv _T is the Doppler width). In the case of interaction of atomic ions with radiation in the optical range, this corresponds to magnetic fields B?600 G (for the ion mass M～10 amu). Noninversive partial velocity amplification of radiation is a “latent” effect in the sense that it disappears upon averaging over all velocity directions of ions. This effect is associated with the emergence of phase incursion of the induced dipole moment oscillations for ions moving in circular cyclotron orbits, which depends on the ion velocity.     

On the ground state energy of free excitons in group IV and III–V semiconductors

An approximate calculation of the ground state energy of direct and indirect free excitons for group IV and group III–V semiconductors is presented. The basic assumption in this treatment is that the anisotropy of the effective masses can be neglected, however, the degeneracy of the valence band cannot. The resulting exciton ground state energy has the usual form but with a reduced mass \(\overline \mu \) given by ( \(\overline \mu \) )^?1=(m _e)^?1+(m _lh)^?1+(m _hh)^?1. The agreement with experiments is considerably improved as compared to the conventional ground state energy comprising the reduced mass defined as (μ)^?1=(m _e)^?1+(m _hh)^?1. Anisotropy corrections are shown to be of minor importance in many cases. However, for the heavier III–V-compounds the neglect of linear terms inE(k) for the valence band results in more serious errors, which invalidate the present theoretical approach.