Singlet-triplet transition in a lateral quantum dot

We study transport through a lateral quantum dot in the vicinity of the singlet-triplet transition in its ground state. This transition, being sharp in an isolated dot, is broadened to a crossover by the exchange interaction of the dot electrons with the conduction electrons in the leads. For a generic set of system's parameters, the linear conductance has a maximum in the crossover region. At zero temperature and magnetic field, the maximum is the strongest. It becomes less pronounced at finite Zeeman splitting, which leads to an increase of the background conductance and a decrease of the conductance in the maximum

Observational physics of mirror world

The existence of the whole world of shadow particles, interacting with each other and having no mutual interactions with ordinary particles except gravity is a specific feature of modern superstring models, being considered as models of the theory of everything. The presence of shadow particles is the necessary condition in the superstring models, providing compensation of the asymmetry of left and right chirality states of ordinary particles. If compactification of additional dimensions retains the symmetry of left and right states, shadow world turns to be the mirror one, with particles and fields having properties strictly symmetrical to the ones of corresponding ordinary particles and fields. Owing to the strict symmetry of physical laws for ordinary and mirror particles, the analysis of cosmological evolution of mirror matter provides rather definite conclusions on possible effects of mirror particles in the universe. A general qualitative discussion of possible astronomical impact of mirror matter is given, in order to make as wide as possible astronomical observational searches for the effects of mirror world, being the unique way to test the existence of mirror partners of ordinary particles in the Nature

Correlations in an expanding gas of hard-core bosons

We consider a longitudinal expansion of a one-dimensional gas of hard-core bosons suddenly released from a trap. We show that the broken translational invariance in the initial state of the system is encoded in correlations between the bosonic occupation numbers in the momentum space. The correlations are protected by the integrability and exhibit no relaxation during the expansion

Dynamic response of one-dimensional interacting fermions

We evaluate the dynamic structure factor $S(q,\omega)$ of interacting one-dimensional spinless fermions with a nonlinear dispersion relation. The combined effect of the nonlinear dispersion and of the interactions leads to new universal features of $S(q,\omega)$. The sharp peak $S\propto q\delta(\omega-uq)$, characteristic for the Tomonaga-Luttinger model, broadens up; $S(q,\omega)$ for a fixed $q$ becomes finite at arbitrarily large $\omega$. The main spectral weight, however, is confined to a narrow frequency interval of the width $\delta\omega\sim q^2/m$. At the boundaries of this interval the structure factor exhibits power-law singularities with exponents depending on the interaction strength and on the wave number $q$

HI study of extremely metal-deficient dwarf galaxies. I. The Nancay Radio Telescope observations of twenty-two objects

The goal of this study is to measure parameters of the integrated HI emission for twenty-two dwarf galaxies with oxygen abundance 12+log(O/H) in the range of 7.42 to 7.65, which are representatives of the eXtremely Metal-Deficient (XMD) galaxy group. Some of them are expected to be similar to the well-known candidates for local young galaxies, IZw18 and SBS 0335-052 that have most of their baryon mass in the form of neutral gas. Therefore, the HI 21-cm line observations are crucial to understanding their group and individual properties. The Nancay Radio Telescope (NRT) with the upgraded focal receiver was used for observations of the 21-cm HI-line. This permitted the detection of the faintest sources with rms of ~1 mJy per 10.5 km/s resolution element. For eighteen detected galaxies we present the parameters of their integrated HI line emission and describe the data on individual objects in more detail. For four undetected XMD galaxies, we give upper limits on their M$(HI). For 70% of the twenty studied non low surface brightness XMD galaxies, we find evidence (both from HI and optical data) for their interaction with neighboring objects. In the brief discussion of the group HI properties of the observed subsample (the total O/H range is of 0.23 dex, or a factor of 1.7), we underline the broad distributions of the HI mass (range is of 2 orders of magnitude), of the ratio M(HI)/L_B (of 1 order of magnitude), and of the blue luminosity (range is of 2 orders of magnitude). We also obtained HI parameters of six galaxies that do not belong to the XMD sample. These data increase the number of XMD galaxies with known integrated HI parameters (or upper limits) by a factor of two. This allows us to address statistical properties of this group, which will be presented in a forthcoming paper. (Abridged).Comment: 11 pages, including 2 tables and 2 postscript figures. Accepted to Astronomy and Astrophysic