250 research outputs found
Constraints on the parameters of radiatively decaying dark matter from the dark matter halo of the Milky Way and Ursa Minor
We improve the earlier restrictions on parameters of the dark matter (DM) in
the form of a sterile neutrino. The results were obtained from non-observing
the DM decay line in the X-ray spectrum of the Milky Way (using the recent
XMM-Newton PN blank sky data). We also present a similar constraint coming from
the recent XMM-Newton observation of Ursa Minor -- dark, X-ray quiet dwarf
spheroidal galaxy. The new Milky way data improve on (by as much as the order
of magnitude at masses ~3.5 keV) existing constraints. Although the observation
of Ursa Minor has relatively poor statistics, the constraints are comparable to
those recently obtained using observations of the Large Magellanic Cloud or
M31. This confirms a recent proposal that dwarf satellites of the MW are very
interesting candidates for the DM search and dedicated studies should be made
to this purpose.Comment: 8 pp. v.2 - Final version to appear in A&
Sterile neutrinos in cosmology and how to find them in the lab
A number of observed phenomena in high energy physics and cosmology lack
their resolution within the Standard Model of particle physics. These puzzles
include neutrino oscillations, baryon asymmetry of the universe and existence
of dark matter. We discuss the suggestion that all these problems can be solved
by new physics which exists only below the electroweak scale. The dedicated
experiments that can confirm or rule out this possibility are discussed.Comment: Invited talk at XXIII Int. Conf. on Neutrino Physics and
Astrophysics, May 25-31, Christchurch, New Zealan
Role of the cyclic lipopeptide massetolide A in biological control of Phytophthora infestans and in colonization of tomato plants by Pseudomonas fluorescens
Pseudomonas strains have shown promising results in biological control of late blight caused by Phytophthora infestans. However, the mechanism(s) and metabolites involved are in many cases poorly understood. Here, the role of the cyclic lipopeptide massetolide A of Pseudomonas fluorescens SS101 in biocontrol of tomato late blight was examined. Pseudomonas fluorescens SS101 was effective in preventing infection of tomato (Lycopersicon esculentum) leaves by P. infestans and significantly reduced the expansion of existing late blight lesions. Massetolide A was an important component of the activity of P. fluorescens SS101, since the massA-mutant was significantly less effective in biocontrol, and purified massetolide A provided significant control of P. infestans, both locally and systemically via induced resistance. Assays with nahG transgenic plants indicated that the systemic resistance response induced by SS101 or massetolide A was independent of salicylic acid signalling. Strain SS101 colonized the roots of tomato seedlings significantly better than its massA-mutant, indicating that massetolide A was an important trait in plant colonization. This study shows that the cyclic lipopeptide surfactant massetolide A is a metabolite with versatile functions in the ecology of P fluorescens SS101 and in interactions with tomato plants and the late blight pathogen P. infestans
Search for the light dark matter with an X-ray spectrometer
Sterile neutrinos with the mass in the keV range are interesting warm dark
matter (WDM) candidates. The restrictions on their parameters (mass and mixing
angle) obtained by current X-ray missions (XMM-Newton or Chandra) can only be
improved by less than an order of magnitude in the near future. Therefore the
new strategy of search is needed. We compare the sensitivities of existing and
planned X-ray missions for the detection of WDM particles with the mass ~1-20
keV. We show that existing technology allows an improvement in sensitivity by a
factor of 100. Namely, two different designs can achieve such an improvement:
[A] a spectrometer with the high spectral resolving power of 0.1%, wide
(steradian) field of view, with small effective area of about cm^2 (which can
be achieved without focusing optics) or [B] the same type of spectrometer with
a smaller (degree) field of view but with a much larger effective area of 10^3
cm^2 (achieved with the help of focusing optics). To illustrate the use of the
"type A" design we present the bounds on parameters of the sterile neutrino
obtained from analysis of the data taken by an X-ray microcalorimeter. In spite
of the very short exposure time (100 sec) the derived bound is comparable to
the one found from long XMM-Newton observation.Comment: 9pp, revtex
The masses of active neutrinos in the nuMSM from X-ray astronomy
In an extention of the Standard Model by three relatively light right-handed
neutrinos (the nuMSM model) the role of the dark matter particle is played by
the lightest sterile neutrino. We demonstrate that the observations of the
extragalactic X-ray background allow to put a strong upper bound on the mass of
the lightest active neutrino and predict the absolute values of the mass of the
two heavier active neutrinos in the nuMSM, provided that the mass of the dark
matter sterile neutrino is larger than 1.8 keV.Comment: 6 pages. revtex
Where to find a dark matter sterile neutrino?
We propose a strategy of how to look for dark matter (DM) particles
possessing a radiative decay channel and derive constraints on their parameters
from observations of X-rays from our own Galaxy and its dwarf satellites. When
applied to the sterile neutrinos in keV mass range, it allows a significant
improvement of restrictions to its parameters, as compared with previous works.Comment: 5 pp, revtex; v3: 1-sigma limits have been replaced by more
conservative 3-sigma limits, a picture illustrating the data analysis methods
has been ade
Effects of resveratrol and SIRT1 on PGC-1α activity and mitochondrial biogenesis: A reevaluation
It has been reported that feeding mice resveratrol activates AMPK and SIRT1 in skeletal muscle leading to deacetylation and activation of PGC-1α, increased mitochondrial biogenesis, and improved running endurance. This study was done to further evaluate the effects of resveratrol, SIRT1, and PGC-1α deacetylation on mitochondrial biogenesis in muscle. Feeding rats or mice a diet containing 4 g resveratrol/kg diet had no effect on mitochondrial protein levels in muscle. High concentrations of resveratrol lowered ATP concentration and activated AMPK in CâCââ myotubes, resulting in an increase in mitochondrial proteins. Knockdown of SIRT1, or suppression of SIRT1 activity with a dominant-negative (DN) SIRT1 construct, increased PGC-1α acetylation, PGC-1α coactivator activity, and mitochondrial proteins in CâCââ cells. Expression of a DN SIRT1 in rat triceps muscle also induced an increase in mitochondrial proteins. Overexpression of SIRT1 decreased PGC-1α acetylation, PGC-1α coactivator activity, and mitochondrial proteins in CâCââ myotubes. Overexpression of SIRT1 also resulted in a decrease in mitochondrial proteins in rat triceps muscle. We conclude that, contrary to some previous reports, the mechanism by which SIRT1 regulates mitochondrial biogenesis is by inhibiting PGC-1α coactivator activity, resulting in a decrease in mitochondria. We also conclude that feeding rodents resveratrol has no effect on mitochondrial biogenesis in muscle
Freeze-In Production of FIMP Dark Matter
We propose an alternate, calculable mechanism of dark matter genesis,
"thermal freeze-in," involving a Feebly Interacting Massive Particle (FIMP)
interacting so feebly with the thermal bath that it never attains thermal
equilibrium. As with the conventional "thermal freeze-out" production
mechanism, the relic abundance reflects a combination of initial thermal
distributions together with particle masses and couplings that can be measured
in the laboratory or astrophysically. The freeze-in yield is IR dominated by
low temperatures near the FIMP mass and is independent of unknown UV physics,
such as the reheat temperature after inflation. Moduli and modulinos of string
theory compactifications that receive mass from weak-scale supersymmetry
breaking provide implementations of the freeze-in mechanism, as do models that
employ Dirac neutrino masses or GUT-scale-suppressed interactions. Experimental
signals of freeze-in and FIMPs can be spectacular, including the production of
new metastable coloured or charged particles at the LHC as well as the
alteration of big bang nucleosynthesis.Comment: 30 pages, 7 figures, PDFLaTex. References adde
Composite Dirac Neutrinos
We present a mechanism that naturally produces light Dirac neutrinos. The
basic idea is that the right-handed neutrinos are composite. Any realistic
composite model must involve `hidden flavor' chiral symmetries. In general some
of these symmetries may survive confinement, and in particular, one of them
manifests itself at low energy as an exact symmetry. Dirac neutrinos are
therefore produced. The neutrinos are naturally light due to compositeness. In
general, sterile states are present in the model, some of them can naturally be
warm dark matter candidates.Comment: 12 pages; Sec. IIC updated; minor corrections; published versio
Dilaton Destabilization at High Temperature
Many compactifications of higher-dimensional supersymmetric theories have
approximate vacuum degeneracy. The associated moduli fields are stabilized by
non-perturbative effects which break supersymmetry. We show that at finite
temperature the effective potential of the dilaton acquires a negative linear
term. This destabilizes all moduli fields at sufficiently high temperature. We
compute the corresponding critical temperature which is determined by the scale
of supersymmetry breaking, the beta-function associated with gaugino
condensation and the curvature of the K"ahler potential, T_crit ~ (m_3/2
M_P)^(1/2) (3/\beta)^(3/4) (K'')^(-1/4). For realistic models we find T_crit ~
10^11-10^12 GeV, which provides an upper bound on the temperature of the early
universe. In contrast to other cosmological constraints, this upper bound
cannot be circumvented by late-time entropy production.Comment: 19 pages, 9 figure
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