2,332 research outputs found
Non-relativistic pair annihilation of nearly mass degenerate neutralinos and charginos II. P-wave and next-to-next-to-leading order S-wave coefficients
This paper is a continuation of an earlier work (arXiv:1210.7928) which
computed analytically the tree-level annihilation rates of a collection of
non-relativistic neutralino and chargino two-particle states in the general
MSSM. Here we extend the results by providing the next-to-next-to-leading order
corrections to the rates in the non-relativistic expansion in momenta and mass
differences, which include leading P-wave effects, in analytic form. The
results are a necessary input for the calculation of the Sommerfeld-enhanced
dark matter annihilation rates including short-distance corrections at
next-to-next-to-leading order in the non-relativistic expansion in the general
MSSM with neutralino LSP.Comment: LaTeX, 16 pages (+ 36 pages Appendix), 4 figures; v2 - new appendix
with analytic results for the P-wave and rest of v^2 corrections to
annihilation rates in the wino limit added, matches published versio
Heavy neutralino relic abundance with Sommerfeld enhancements - a study of pMSSM scenarios
We present a detailed discussion of Sommerfeld enhancements in neutralino
dark matter relic abundance calculations for several popular benchmark
scenarios in the general MSSM. Our analysis is focused on models with heavy
wino- and higgsino-like neutralino LSP and models interpolating between these
two scenarios. This work is the first phenomenological application of effective
field theory methods that we have developed in earlier work and that allow for
the consistent study of Sommerfeld enhancements in non-relativistic neutralino
and chargino co-annihilation reactions within the general MSSM, away from the
pure-wino and pure-higgsino limits.Comment: 38 pages, 14 figures, 3 table
Non-relativistic pair annihilation of nearly mass degenerate neutralinos and charginos I. General framework and S-wave annihilation
We compute analytically the tree-level annihilation rates of a collection of
non-relativistic neutralino and chargino two-particle states in the general
MSSM, including the previously unknown off-diagonal rates. The results are
prerequisites to the calculation of the Sommerfeld enhancement in the MSSM,
which will be presented in subsequent work. They can also be used to obtain
concise analytic expressions for MSSM dark matter pair annihilation in the
present Universe for a large number of exclusive two-particle final states.Comment: LATeX, 24 pages (+ 25 pages Appendix), 11 figures; v2 - replaced
incorrect version of Fig. 4 and fixed typos listed in the JHEP erratu
Magnetism in 2D BNO and BSiN: polarized itinerant and local electrons
We use density functional theory based first-principles methods to study the
magnetism in a 2D hexagonal BN sheet induced by the different concentrations of
oxygen and silicon atoms substituting for nitrogen (O) and boron
(Si) respectively. We demonstrate the possible formation of three
distinct phases based on the magnetization energy calculated self-consistently
for the ferromagnetic (ME) and antiferromagnetic
(ME) states, i.e. the paramagnetic phase with
ME=ME, the ferromagnetic phase with
MEME and finally the polarized itinerant
electrons with finite ME but zero ME. While
the O system was found to exist in all three phases, no tendency
towards the formation of the polarized itinerant electrons was observed for the
Si system though the existence of the other two phases was
ascertained. The different behavior of these two systems is associated with the
diverse features in the magnetization energy as a function of the oxygen and
silicon concentrations. Finally, the robustness of the polarized itinerant
electron phase is also discussed with respect to the O substitute atom
distributions and the applied strains to the system.Comment: accepted by RP
Analysis of band-gap formation in squashed arm-chair CNT
The electronic properties of squashed arm-chair carbon nanotubes are modeled
using constraint free density functional tight binding molecular dynamics
simulations. Independent from CNT diameter, squashing path can be divided into
{\it three} regimes. In the first regime, the nanotube deforms with negligible
force. In the second one, there is significantly more resistance to squashing
with the force being nN/per CNT unit cell. In the last regime,
the CNT looses its hexagonal structure resulting in force drop-off followed by
substantial force enhancement upon squashing. We compute the change in band-gap
as a function of squashing and our main results are: (i) A band-gap initially
opens due to interaction between atoms at the top and bottom sides of CNT. The
orbital approximation is successful in modeling the band-gap opening at
this stage. (ii) In the second regime of squashing, large
interaction at the edges becomes important, which can lead to band-gap
oscillation. (iii) Contrary to a common perception, nanotubes with broken
mirror symmetry can have {\it zero} band-gap. (iv) All armchair nanotubes
become metallic in the third regime of squashing. Finally, we discuss both
differences and similarities obtained from the tight binding and density
functional approaches.Comment: 16 pages and 6 figures, To appear in PR
Relic density of wino-like dark matter in the MSSM
The relic density of TeV-scale wino-like neutralino dark matter in the MSSM
is subject to potentially large corrections as a result of the Sommerfeld
effect. A recently developed framework enables us to calculate the
Sommerfeld-enhanced relic density in general MSSM scenarios, properly treating
mixed states and multiple co-annihilating channels as well as including
off-diagonal contributions. Using this framework, including on-shell one-loop
mass splittings and running couplings and taking into account the latest
experimental constraints, we perform a thorough study of the regions of
parameter space surrounding the well known pure-wino scenario: namely the
effect of sfermion masses being non-decoupled and of allowing non-negligible
Higgsino or bino components in the lightest neutralino. We further perform an
investigation into the effect of thermal corrections and show that these can
safely be neglected. The results reveal a number of phenomenologically
interesting but so far unexplored regions where the Sommerfeld effect is
sizeable. We find, in particular, that the relic density can agree with
experiment for dominantly wino neutralino dark matter with masses ranging from
1.7 to beyond 4 TeV. In light of these results the bounds from Indirect
Detection on wino-like dark matter should be revisited.Comment: 49 pages, 15 figure
Ab initio Studies of the Possible Magnetism in BN Sheet by Non-magnetic Impurities and Vacancies
We performed first-principles calculations to investigate the possible
magnetism induced by the different concentrations of non-magnetic impurities
and vacancies in BN sheet. The atoms of Be, B, C, N, O, Al and Si are used to
replace either B or N in the systems as impurities. We discussed the changes in
density of states as well as the extent of the spatial distributions of the
defect states, the possible formation of magnetic moments, the magnitude of the
magnetization energies and finally the exchange energies due to the presence of
these defects. It is shown that the magnetization energies tend to increase as
the concentrations of the defects decreases in most of the defect systems which
implies a definite preference of finite magnetic moments. The calculated
exchange energies are in general tiny but not completely insignificant for two
of the studied defect systems, i.e. one with O impurities for N and the other
with B vacancies.Comment: 8 pages, 10 figures, submitted to Phys. Rev.
Fluctuation-induced forces between inclusions in a fluid membrane under tension
We discuss the fluctuation-induced force, a finite-temperature analog of the
Casimir force, between two inclusions embedded in a fluid membrane under
tension. We suggest a method to calculate this Casimir interaction in the most
general case, where membrane fluctuations are governed by the combined action
of surface tension, bending modulus, and the Gaussian rigidity. We find that
the surface tension strongly modifies the power law in the separation
dependence of the Casimir interaction. This results in a strong suppression of
the Casimir force at separations beyond a characteristic length, which could
affect protein aggregation dynamics in cell membranes.Comment: 4 pages, 1 figur
Venture Capital in Japan: A Financial Instrument Supporting the Innovativeness of the Japanese Economy
Two factors: First, the relatively small number of new companies as well as the number of companies subject to liquidation over the year ("firm turnover") in Japan, and second, the insignificant prestige associated with the profession of entrepreneur do not foster growth in the dynamics of this form of financing ventures. The cited indicator for Japan in among the lowest in comparison with other highly developed countries1, while the profession of entrepreneur is not the foremost dream of college graduates. They would much rather prefer realizing their professional careers as members of the government bureaucracy or employees of a major corporation2. However, this mindset is slowly changing, if for no other reason then, in spite of popular conviction, because most small companies are not established during periods of prosperity, but near the end of the downward phase of the economic cycle. That is exactly the phase Japan has been dealing with for several years now. Young, creative people, recruited from the unemployed, are seeking self-employment, using all possible opportunities embedded in the "again starting up" machinery of the economy.Dwa czynniki: pierwszy - stosunkowo mała liczba nowych firm, a także firm likwidowanych w skali roku ("firm turnover") w Japonii oraz drugi - niewielki prestiż, jakim cieszy się zawód przedsiębiorcy, nie sprzyjają dynamizacji omawianej formy finansowania przedsięwzięć. Cytowany wskaźnik, dla Japonii należy do najniższych w porównaniu z innymi krajami wysoko rozwiniętymi (Grabowiecki 2000), zaś profesja przedsiębiorcy nie jest szczytem marzeń ludzi po studiach. Znacznie bardziej chcieliby oni swoją karierę zawodową realizować jako członkowie rządowej biurokracji lub pracownicy dużej korporacji (Corver 2008, s. 2). Ta świadomość ulega jednak stopniowej zmianie, chociażby dlatego, że wbrew popularnym przekonaniom, większość niewielkich przedsiębiorstw, powstaje nie w okresie prosperity, lecz pod koniec spadkowej fazy cyklu koniunkturalnego. Z taką fazą mamy do czynienia w Japonii od paru lat. Młodzi, kreatywni ludzie, rekrutujący się z bezrobotnych, poszukują samozatrudnienia, wykorzystują wszelakie szanse, tkwiące w "ruszającej na powrót" maszynerii gospodark (Yonekura, Lynskey 2003, s. 11)
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