1,494 research outputs found
The quark strange star in the enlarged Nambu-Jona-Lasinio model
The strange quark star is investigated within the enlarged SU(3)
Nambu-Jona-Lasinio (NJL). The stable quark star exists till maximal
configutation with rho_m=3.1, 10^15, g/cm^3 with M_m=1.61, M_Sun and R_m=8.74,
km is reached. Strange quarks appear for density above rho_c=9.84 g/cm^3 for
the quark star with radius R_c=8.003 km and M_c=0.77, M_Sun. The comparison of
a quark star properties obtained in the Quark Mean Field (QMF) approach to a
neutron star model constructed within the Relativistic Mean Field (RMF) theory
is presented.Comment: 23 pages, iop latex2e + hyperref, 11 figures, to appear in NJ
Photon-Photon Absorption of Very High Energy Gamma-Rays from Microquasars: Application to LS 5039
Very high energy (VHE) gamma-rays have recently been detected from the
Galactic black-hole candidate and microquasar LS 5039. A plausible site for the
production of these VHE gamma-rays is the region close to the mildly
relativistic outflow. However, at distances comparable to the binary
separation, the intense photon field of the stellar companion will lead to
substantial gamma-gamma absorption of VHE gamma-rays. If the system is viewed
at a substantial inclination (i > 0), this absorption feature will be modulated
on the orbital period of the binary as a result of a phase-dependent
stellar-radiation intensity and pair-production threshold. We apply our results
to LS 5039 and find that (1) gamma-gamma absorption effects will be substantial
if the photon production site is located at a distance from the central compact
object of the order of the binary separation (~ 2.5e12 cm) or less; (2) the
gamma-gamma absorption depth will be largest at a few hundred GeV, leading to a
characteristic absorption trough; (3) the gamma-gamma absorption feature will
be strongly modulated on the orbital period of the binary, characterized by a
spectral hardening accompanying periodic dips of the VHE gamma-ray flux; and
(4) gamma rays can escape virtually unabsorbed, even from within ~ 10^{12} cm,
when the star is located behind the production site as seen by the observer.Comment: Submitted to ApJ Letters. AASTeX, 12 ms pages, including 4 eps
figure
Gated combo nanodevice for sequential operations on single electron spin
An idea for a nanodevice in which an arbitrary sequence of three basic
quantum single qubit gates - negation, Hadamard and phase shift - can be
performed on a single electron spin. The spin state is manipulated using the
spin-orbit coupling and the electron trajectory is controlled by the electron
wave function self-focusing mechanism due to the electron interaction with the
charge induced on metal gates. We present results of simulations based on
iterative solution of the time dependent Schr\"odinger equation in which the
subsequent operations on the electron spin can be followed and controlled.
Description of the moving electron wave packet requires evaluation of the
electric field within the entire nanodevice in each time step
Occurrence of the neotropical moss Dicranella hilariana (Mont.) Mitt. in the Antarctic
Dicranella hilariana (Mont.) Mitt., a pan-neotropical moss species, is reported for the first time from the Antarctic botanical zone. It was found on geothermally heated ground near fumaroles on Visokoi, Candlemas and Bellingshausen Islands in the volcanic archipelago of the South Sandwich Islands. Dicranella recurvata Ochyra, Arts & Lewis-Smith, nom. nud., is reduced to synonymy with D. hilariana. The Antarctic plants of D. hilariana are briefly described and illustrated, including the rhizoidal tubers which have not previously been reported in this species. The global distribution of D. hilariana is briefly reviewed and mapped. It is suggested that the species reached the Antarctic via long-distance dispersal from South America by the prevailing strong westerly winds
Hyperons in neutron-star cores and two-solar-mass pulsar
Recent measurement of mass of PSR J1614-2230 rules out most of existing
models of equation of state (EOS) of dense matter with high-density softening
due to hyperonization or a phase transition to quark matter or a boson
condensate.
We look for a solution of an apparent contradiction between the consequences
stemming from up-to-date hypernuclear data, indicating appearance of hyperons
at 3 nuclear densities and existence of a two-solar-mass neutron star.
We consider a non-linear relativistic mean field (RMF) model involving baryon
octet coupled to meson fields. An effective lagrangian includes quartic terms
in the meson fields. The values of the parameters of the model are obtained by
fitting semi-empirical parameters of nuclear matter at the saturation point, as
well as potential wells for hyperons in nuclear matter and the strength of the
Lambda-Lambda attraction in double-Lambda hypernuclei.
We propose a non-linear RMF model which is consistent with up-to-date
semiempirical nuclear and hypernuclear data and allows for neutron stars with
hyperon cores and M larger than 2 solar masses. The model involves
hidden-strangenes scalar and vector mesons, coupled to hyperons only, and
quartic terms involving vector meson fields.
Our EOS involving hyperons is stiffer than the corresponding nucleonic EOS
(with hyperons artificially suppressed) above five nuclear densities. Required
stiffening is generated by the quartic terms involving hidden-strangeness
vector meson.Comment: 7 pages, 5 figures. Main results of this paper were already presented
at the MODE-SNR-PWN Workshop in Bordeaux, France, November 15-17, 2010, and
in a poster at the CompStar 2011 Workshop in Catania, Italy, May 9-12, 2011.
The paper is being submitted to Astronomy & Astrophysic
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