Enhancement of dark matter relic density from late time dark matter conversions

We demonstrate that if the dark matter (DM) in the Universe contains multiple components, the possible interactions between the DM components may convert the heavier DM components into lighter ones. It is then possible that the lightest DM component with an annihilation cross section significantly larger than that of the typical weakly interacting massive particle (WIMP) may lead to a relic density in agreement with cosmological observations, due to an enhancement of number density from the DM conversion process at late time after the thermal decoupling. This may provide an alternative source of boost factor relevant to the positron and electron excesses reported by the recent DM indirect search experiments.     

The frequency dependent relaxation time of free carriers in PbSnTe

The recently observed frequency dependence of free carrier relaxation time in the plasma reflectivity studies of semiconductors is accounted for on a two carrier model by including the energy dependence of carrier relaxation time. The results are discussed with special reference to the case of p-type PbSnTe.     

Dark matter, neutron stars, and strange quark matter

We show that self-annihilating weakly interacting massive particle (WIMP) dark matter accreted onto neutron stars may provide a mechanism to seed compact objects with long-lived lumps of strange quark matter, or strangelets, for WIMP masses above a few GeV. This effect may trigger a conversion of most of the star into a strange star. We use an energy estimate for the long-lived strangelet based on the Fermi-gas model combined with the MIT bag model to set a new limit on the possible values of the WIMP mass that can be especially relevant for subdominant species of massive neutralinos.     

Theoretical calculation of turn-on delay time of VCSEL and effect of carriers recombination

It is known that the turn-on delay time, t_d, for semiconductor lasers depends on the functional form of the recombination rate. Previously, an analytic expression for t_d had been obtained, following simple approximations. In this paper, on the basis of the rate equations for quantum well vertical cavity surface emitting lasers (VCSEL), an explicit analytical expression for the turn-on delay of the VCSEL has also been deduced for the general case. The time evolution of the carrier density within the turn-on period of VCSEL has been derived for the case, where the Auger effect is considered as a term proportional to the cube of the carrier density.     

Mind,matter, and physicists

Some aspects of the problem of measurement in quantum theory are treated. We stress that the problem is both physical and conceptual, that the physical problem has been solved and the conceptual one is inherent in quantum theory. We also deal with some remarks made by Wigner concerning physics and the explanation of life, and present alternative positions on the mind-matter relationship within a deterministic framework, as we see them.     

Superheavy matter, strange matter, antimatter and the structure of the vacuum

The extension of the periodic system into various new areas is investigated. Experiments for the synthesis of superheavy elements and the predictions of magic numbers are reviewed. Further on, investigations on hypernuclei and the possible production of antimatter clusters in heavy-ion collisions are reported. Various versions of the meson field theory serve as effective field theories at the basis of modern nuclear structure and suggest structure in the vacuum which might be important for the production of hyper- and antimatter.     

How to measure diffusion constant and absolute susceptibility of charge carriers at the same time

Multiple spin echos can be excited for spin-1/2 systems by two radiofrequency pulses with tipping angles unequal to 180°, if the absolute magnetization is sufficiently large. If a magnetic field gradient is applied, the attenuation of the primary echo reveals the diffusion constant of these spins, whereas the ratio of primary and secondary echo amplitudes indicates the absolute magnetic susceptibility of the resonating spins. This potentiality is examined here numerically and by application of nuclear magnetic resonance to liquid samples containing protons. We analyse the complications that have to be overcome, if this technique is used for the study of the charge and spin carriers in low-symmetry quasi-one-dimensional organic conductors. Reasonable accuracy is obtained for the parameters derived for the conduction electrons of perylene radical cation salts.     

Reflectivity and transmittance investigations of photoexcited charge carriers in silicon in the picosecond time domain

Using picosecond laser pulses of a NdYAG laser system we studied relaxation processes in high-excited monocrystalline silicon by transient reflectivity and transmittance. An experimental setup will be presented which is very sensitive to small refractive index changes. By different excitation radiations, i.e. different induced carrier distributions it is possible to separate the influence of different relaxation processes as surface and bulk recombination and diffusion on the simultaneously measured transient reflectivity and transmittance. The parameters of these relaxation processes were found by fitting the experimental results with computer calculations.     

Mind,matter, and quantum mechanics

A theory of psychophysical phenomena is proposed. It resolves simultaneously four basic problems of science, namely the problems of the connections between:(1) mind and matter,(2) quantum theory and reality,(3) relativity theory and becoming, and (4) relativity theory and Bell's theorem.This work was supported by the Director, Office of Energy Research, Office of High Energy and Nuclear Physics, Division of High Energy Physics of the U.S. Department of Energy under Contract W-7405-EN-G-48.     

Picosecond dynamics of quantum structure carriers measured by time resolved photoinduced intersubband absorption

A novel interband-pump intersubband-probe technique is developed in order to study the dynamics of photogenerated carriers and excitons in GaAs/AlGaAs superlattices by time resolved photoinduced absorption. The photogenerated population reaches a thermal distribution a few picoseconds after the excitation. The time dependence of the intersubband absorption strength and its time resolved excitation spectra yield a measure for the time it takes for that population to cool first to the lattice temperature and then to radiatively decay. The first time is roughly 70-100 ps depending on the excess energy with which the photogenerated carriers are created. The second is on a sub-nanosecond scale and depends linearly on the lattice temperature.     

On the investigation of laser-induced carriers in silicon in the picosecond time range

The dependence of the time behaviour of optically-induced carriers on linear recombination and diffusion is studied taking into account the exciting pulse duration. If the pulse duration becomes comparable to the carrier lifetime in the case of linear recombination the exciting pulse influences the temporal behaviour of the carriers significantly. If the temporal behaviour of the carriers is to be determined by diffusion an exciting pulse, short with respect to a characteristic diffusion time, strongly influences this behaviour. These calculations were used to fit some experimental results of time-resolved reflectivity measurements of silicon.

---

Zusammenfassung Es wird das zeitliche Verhalten von optisch angeregten Ladungsträgern bei linearer Rekombination und Diffusion unter Berücksichtigung der Anregungsimpulslänge untersucht. Während die Anregungsimpulslänge im Fall der linearen Rekombination erst einen merklichen Einfluß auf das Zeitverhalten der Ladungsträger gewinnt, wenn sie in die Größe der Rekombinationszeit gelangt, wird ihr Einfluß auf das Diffusionsverhalten bemerkbar, wenn sie klein gegen die Diffusionszeit ist. Die numerischen Rechnungen wurden zur Interpretation von zeitaufgelösten Reflexionsmessungen an Silizium angewandt.

     

Formation time of hadrons and density of matter produced in relativistic heavy-ion collisions

Density of matter produced in relativistic heavy-ion collisions depends substantially on the spacetime evolution of the collision and on the formation time of hadrons produced. Interactions of hadrons younger than their formation time are attenuated with respect to their normal values (transparency of hadronic matter for newly formed hadrons). The system of secondary hadrons produced in a heavy-ion collision thus expands as a gas of almost non interacting particles before hadrons reach their formation time. Densities of interacting hadronic matter produced in oxygen-lead and sulphur-lead collisions at 200 GeV/nucleon are estimated as a function of the formation time of hadrons. Uncertainties in our knowledge of the critical temepratureT _c and of the formation time of hadrons τ₀ permit at present three scenarios: an optimistic one (QGP has already been produced in collisions of oxygen and sulphur with heavy ions and will be copiously produced in Lead collisions), a pessimistic one (QGP cannot be produced at 200 GeV/nucleon) and an intermediate one (QGP has not been produced in oxygen and sulphur interactions with heavy ions and will be at best produced only marginally in Pb-collisions). We find the last opinion as most probable.     

Theory of a Pair of Quantum Bits

In this paper we present a thorough study of the theory of a pair of qubits, whose Hilbert space can be identified with ^{2 2}. Given an hermitian operator of trace 1 in ^{2 2} we focus on the following Problems: Problem 1: Find conditions that guarantee that is a state, that is, positive semidefinite. Problem 2: Find conditions that guarantee that a given state is separable, or that is a convex combination of products of one-particle states. The language we develop for our investigation makes use of the observation that ^{2 2} carries representations of the special unitary group SU(2) in two dimensions and of the direct product of this group by itself. We introduce a new type of observable called Bell observable (section 5) and a new measure of entanglement called concurrence, which is closely related to the concurrence introduced by Wootters (Physical Review Letters (1998) 80, 2245–2248) (section 8). The work has been inspired by the works of Wootters (Physical Review Letters (1997) 78, 5022–5025; Physical Review Letters (1998) 80, 2245–2248) and members of the Horodecki family (cf Horodecki and Horodecki, Physical Review A (1996) 54, 1838–1843; Horodecki et al., Physics Letters A (1996a) 223, 1–8; Physics Letters A (1996b) 222, 21–25) and reproduces some of their results.     

Probing the space- time evolution of hot parton matter by hard jets

The propagation of hard parton jets through an expanding quark-gluon plasma is investigated in the framework of hydrodynamical approach. The influence of viscosity and transverse expansion of plasma on the intensity of jet rescattering is estimated for initial conditions, predicted to be achieved at LHC. The sensitivity of jet quenching and dijet acoplanarity to the space-time evolution of hot parton matter created in ultrarelativistic heavy ion collisions is analyzed.     

Warped unification, proton stability, and dark matter

We show that solving the problem of baryon-number violation in nonsupersymmetric grand unified theories (GUT's) in warped higher-dimensional spacetime can lead to a stable Kaluza-Klein particle. This exotic particle has gauge quantum numbers of a right-handed neutrino, but carries fractional baryon number and is related to the top quark within the higher-dimensional GUT. A combination of baryon number and SU(3) color ensures its stability. Its relic density can easily be of the right value for masses in the 10 GeV-few TeV range. An exciting aspect of these models is that the entire parameter space will be tested at near future dark matter direct detection experiments. Other exotic GUT partners of the top quark are also light and can be produced at high energy colliders with distinctive signatures.     

PAMELA,FGST and sub-TeV dark matter

PAMELA's observation that the cosmic ray positron fraction increases rapidly with energy implies the presence of primary sources of energetic electron–positron pairs. Of particular interest is the possibility that dark matter annihilations in the halo of the Milky Way provide this anomalous flux of antimatter. The recent measurement of the cosmic ray electron spectrum by the Fermi Gamma Ray Space Telescope, however, can be used to constrain the nature of any such dark matter particle. In particular, it has been argued that in order to accommodate the observations of Fermi and provide the PAMELA positron excess, annihilating dark matter particles must be as massive as ∼1 TeV or heavier. In this Letter, we revisit Fermi's electron spectrum measurement within the context of annihilating dark matter, focusing on masses in the range of 100–1000 GeV, and considering effects such as variations in the astrophysical backgrounds from the presence of local cosmic ray accelerators, and the finite energy resolution of the Fermi Gamma Ray Space Telescope. When these factors are taken into account, we find that dark matter particles as light as ∼300 GeV can be capable of generating the positron fraction observed by PAMELA.