The triple-alpha-reaction at low temperatures

We have studied the triple-α-reaction at low temperatures which is of importance on accreting white dwarfs and neutron stars. Although we have improved a recent investigation of Nomoto, Thielemann and Miyaji on several points, we find a reaction rate for the relevant temperature range (T=10⁷?10⁸K) which is rather similar to the previous result. In particular, our improved study confirms that helium might be ignited on accreting white dwarfs at temperaturesT≦4.10⁷ K.     

Light quarks at low temperatures

We show that for small quark masses, low temperatures and large volumes, the main features of the QCD partition function can be predicted on the basis of chiral symmetry. In particular, we establish a low-temperature theorem which governs the temperature dependence of the fermion condensate.     

Baryogenesis at low reheating temperatures

We note that the maximum temperature during reheating can be much greater than the reheating temperature T(r) at which the universe becomes radiation dominated. We show that the standard model anomalous (B+L)-violating processes can therefore be in thermal equilibrium for 1 GeV less, similarT(r)<100 GeV. Electroweak baryogenesis could work and the traditional upper bound on the Higgs mass coming from the requirement of the preservation of the baryon asymmetry may be relaxed. Alternatively, the baryon asymmetry may be reprocessed by sphaleron transitions either from a (B-L) asymmetry generated by the Affleck-Dine mechanism or from a chiral asymmetry between e(R) and e(L) in a B-L = 0 universe.     

Photoconductivity of semiconductors at low temperatures

Low-temperature oscillations in the photoconductivity of semiconductors are discussed. It is shown that oscillations will be observed if the probability for energy relaxation with optical phonons exceeds both the probability of carrier recombination and the energy-relaxation time for acoustic phonons. The oscillation shape is studied for momentum relaxation with acoustic phonons and with ionized impurities for the case in which interelectronic collisions can be neglected and when an account of these collisions leads to the establishment of an electron temperature.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 85–92, September, 1968.     

Vacancies in a strongly strained crystal at low temperatures

It is shown that an equilibrium vacancy concentration can be noticeable even at a temperature close to absolute zero. This will be the case if the volume deformation of a crystal is higher than a critical value, which is a second-order phase transition point.     

Electron and phonon mechanisms of friction in crystalline solids in atomically close contact at low temperatures

Recent experimental and theoretical studies have shown that an atomically close contact between two crystalline solids can be free from friction of rest in the event that their lattice constants are incommensurate and the interaction at their interface does not exceed a certain threshold value. In this case, the sole mechanisms of friction are the phonon emission and the excitation of conduction electrons. Theoretical estimations of both phonon and electron contributions to the frictional force have been carried out (the latter contribution has been considered both in the normal and superconducting states of metal).     

Thermomagnetic effect in a Knudsen gas at low temperatures

The thermomagnetic effect (TME) in nitrogen interacting with a gold surface is investigated. It has been found that at temperatures T<100K the sign of the effect and the dependence of the heat flux on the magnitude and direction of the field do change.     

Josephson current through a half metal at low temperatures

We study the Josephson effect in the superconductor/diffusive half metal/superconductor junctions by using the recursive Green function method. In the presence of spin-flip scatterings at the interface, odd-frequency spin-triplet Cooper pairs penetrate deeply into a half metal and carry Josephson current. The critical Josephson current increases with decreasing temperatures near the transition temperature. At low temperatures, however, the critical current decreases with decreasing temperatures. Such reentrant behavior is unusual in the case of s-wave superconductor junctions. The penetration of odd-frequency pairs modifies quasiparticle density of states in a half metal near the Fermi energy, which is responsible for the nonmonotonic temperature dependence of critical Josephson current.     

Relaxation in glasses at low temperatures

JETP Letters - The interaction between tunneling system inherent in amorphous solids is established to be responsible for the universal behavior of their kinetics and thermodynamic properties at...     

Quintessential inflation at low reheating temperatures

We have tested some simple quintessential inflation models, imposing the requirement that they match with the recent observational data provided by the BICEP and Planck team and leading to a reheating temperature, which is obtained via gravitational particle production after inflation, supporting the nucleosynthesis success. Moreover, for the models coming from supergravity one needs to demand low temperatures in order to avoid problems such as the gravitino overproduction or the gravitational production of moduli fields, which are obtained only when the reheating temperature is due to the production of massless particles with a coupling constant very close to its conformal value.     

High pressure techniques at low temperatures

Pramana - The article reviews the experimental techniques used in high pressure-low temperature investigations to study a variety of physico-chemical phenomena. The general principles of producing...     

Transitions in glasses at low temperatures

Length-temperature measurements from ?180°C to the glass transition temperature have been made on a poly(vinyl alkyl ether) series, poly(ethylene terephthalate), and a tetrafluoroethylene-trifluoropropylene copolymer series.

Consistent with low frequency dynamic measurements, the poly(vinyl alkyl ethers) exhibit a glass-glass transition? Tgg [1] between Tg and Tg ?70°C with evidence of another at about ?160 to ?180°C. With increasing side-chain length, the expansion coefficient below Tg- and the magnitude of the g-g transition increase, and the value of the Simha-Boyer free-volume product decreases, suggesting retention of excess free volume by the flexible pendant group. This behavior is analogous to that observed for poly(alkyl methacrylates) except that the latter system exhibited two g-g transitions, the lower of which coincided with Tgg [1] observed here.

Poly(ethylene terephthalate) samples, both amorphous and crystalline, exhibit two T > Tg transitions at about ?85 and ?40°C. Dynamic results resolve only one relaxation in this temperature range.

The glass temperatures of the tetrafluoroethylene-trifluoropropylene copolymer series, as determined by both dilatometry and differential scanning calorimetry, extrapolate to a Tg, for 100% amorphous PTFE of 11-16°C. Two g-g transitions, present in each homo-polymer, persist in the copolymers, indicating that only a small number of molecular units are involved. The magnitude of these relaxations, however, as measured by the change in expansion coefficient, is dependent on copolymer composition.     

Cosmological baryon generation at low temperatures

Mechanisms for generating the net baryon number of the universe which do not involve grand unification are considered. Detailed calculations in a simple extension of the standard SU(3)×SU(2)×U(1) model are used to show that physics at temperatures of order 1 TeV can account for the observed baryon to entropy ratio. Some comments regarding alternatives to this simple model and some speculations concerning the implications for cosmology are offered.     

High field magnetoresistance at low temperatures

To explain recent experiments on n-InSb we calculate the transverse and longitudinal electrical conductivity in strong magnetic fields. We consider a free electron-point impurity system in the generalized Born approximation, and in the self-consistentt-matrix approximation. The position, shape and amplitude of the Shubnikovde Haas oscillations and the quantum limit behaviour are in good agreement with experiment.