3,487 research outputs found
Testing Supersymmetry with Lepton Flavor Violating tau and mu decays
In this work the following lepton flavor violating and decays
are studied: , , , , and . We work in a supersymmetric scenario consisting of the minimal
supersymmetric standard model particle content, extended by the addition of
three heavy right handed Majorana neutrinos and their supersymmetric partners,
and where the generation of neutrino masses is done via the seesaw mechanism.
Within this context, a significant lepton flavor mixing is generated in the
slepton sector due to the Yukawa neutrino couplings, which is transmited from
the high to the low energies via the renormalization group equations. This
slepton mixing then generates via loops of supersymmetric particles significant
contributions to the rates of and the correlated decays. We analize here in full detail these rates in terms of the
relevant input parameters, which are the usual minimal supergravity parameters
and the seesaw parameters. For the decays, a full one-loop
analytical computation of all the contributing supersymmetric loops is
presented. This completes and corrects previous computations in the literature.
In the numerical analysis compatibility with the most recent experimental upper
bounds on all these and decays, with the neutrino data, and with
the present lower bounds on the supersymmetric particle masses are required.
Two typical scenarios with degenerate and hierarchical heavy neutrinos are
considered. We will show here that the minimal supergravity and seesaw
parameters do get important restrictions from these and decays in
the hierarchical neutrino case.Comment: Version to appear in Physical Review
Generation of broad XUV continuous high harmonic spectra and isolated attosecond pulses with intense mid-infrared lasers
We present experimental results showing the appearance of a near-continuum in
the high-order harmonic generation (HHG) spectra of atomic and molecular
species as the driving laser intensity of an infrared pulse increases. Detailed
macroscopic simulations reveal that these near-continuum spectra are capable of
producing IAPs in the far field if a proper spatial filter is applied. Further,
our simulations show that the near-continuum spectra and the IAPs are a product
of strong temporal and spatial reshaping (blue shift and defocusing) of the
driving field. This offers a possibility of producing IAPs with a broad range
of photon energy, including plateau harmonics, by mid-IR laser pulses even
without carrier-envelope phase stabilization.Comment: 7 pages, 5 figures, submitted to J.Phys. B (Oct 2011
Probing the Higgs mechanism via
We investigate the sensitivity of the reaction to
the Higgs sector based on the complete one-loop corrections in the minimal
Standard Model and the gauged non-linear -model. While this sensitivity
is very strong for the suppressed cross-section of equally polarized photons
and longitudinal W bosons, it is only marginal for the dominant mode of
transverse polarizations. The corrections within the -model turn out to
be UV-finite in accordance with the absence of \log\MH terms in the Standard
Model with a heavy Higgs boson.Comment: 12 pages uuencoded postscrip
Analysis of the evolution of Xe-135 in a KWU-PWR reactor using coupled codes
[EN] The fission product Xe-135 has a tremendous impact on the operation of the nuclear reactor and may interfere with the plant's operational capacity. Therefore, the incorporation of Flexible Operation (non baseload) in nuclear power plants requires studies that assess the effect of Xenon oscillations in power production taking into account the requirements of the electrical network as well as the nuclear safety.
To analyze the evolution of the neutronic poison Xe-135, a 3D thermal-hydraulic-neutronic model of the core of a pressurized water nuclear reactor (PWR), with three cooling loops and German Siemens-KWU technology, was developed with the coupled code RELAP5/PARCSv3.2. The model was carried out from the real information of the core state and taking into account the data referring to the position of the Incore detectors of the studied plant.
After validating the 3D thermal-hydraulic-neutronic RELAP5/PARCSv3.2 model, an operational transient of the PWR-KWU reactor is carried out in non-baseload operation.
The results verified that the modeling provides good accuracy in predicting the trend of Xenon oscillation behavior. Furthermore, Xenon oscillations in the reactor core are dampened in the same way although the control bank insertion is executed at different ramp rates.
The final goal is to use this model in order to define a strategy to move the control rod banks when there is a requirement to decrease the power in the reactor core.The authors would like to acknowledge the economic support provided by CNAT for the
realization of this work and express their great appreciation to CNAT and IBERDROLA for
sharing the data needed to develop this work.Navarro, B.; Barrachina, T.; Miró Herrero, R.; Verdú Martín, GJ.; Garcia-Fenoll, M.; Posada, JM. (2021). Analysis of the evolution of Xe-135 in a KWU-PWR reactor using coupled codes. European Nuclear Society. 1-10. http://hdl.handle.net/10251/19108711
The Ultraviolet Spectrum and Physical Properties of the Mass Donor Star in HD 226868 = Cygnus X-1
We present an examination of high resolution, ultraviolet spectroscopy from
Hubble Space Telescope of the photospheric spectrum of the O-supergiant in the
massive X-ray binary HD 226868 = Cyg X-1. We analyzed this and ground-based
optical spectra to determine the effective temperature and gravity of the O9.7
Iab supergiant. Using non-local thermodynamic equilibrium (non-LTE), line
blanketed, plane parallel models from the TLUSTY grid, we obtain T_eff = 28.0
+/- 2.5kK and log g > 3.00 +/- 0.25, both lower than in previous studies. The
optical spectrum is best fit with models that have enriched He and N
abundances. We fit the model spectral energy distribution for this temperature
and gravity to the UV, optical, and IR fluxes to determine the angular size of
and extinction towards the binary. The angular size then yields relations for
the stellar radius and luminosity as a function of distance. By assuming that
the supergiant rotates synchronously with the orbit, we can use the radius -
distance relation to find mass estimates for both the supergiant and black hole
as a function of the distance and the ratio of stellar to Roche radius. Fits of
the orbital light curve yield an additional constraint that limits the
solutions in the mass plane. Our results indicate masses of 23^{+8}_{-6} M_sun
for the supergiant and 11^{+5}_{-3} M_sun for the black hole.Comment: ApJ in pres
The nature of supernovae 2010O and 2010P in Arp 299 - II. Radio emission
We report radio observations of two stripped-envelope supernovae (SNe), 2010O
and 2010P, which exploded within a few days of each other in the luminous
infrared galaxy Arp 299. Whilst SN 2010O remains undetected at radio
frequencies, SN 2010P was detected (with an astrometric accuracy better than 1
milli arcsec in position) in its optically thin phase in epochs ranging from ~1
to ~3yr after its explosion date, indicating a very slow radio evolution and a
strong interaction of the SN ejecta with the circumstellar medium. Our
late-time radio observations toward SN 2010P probe the dense circumstellar
envelope of this SN, and imply a mass-loss rate (Msun/yr) to wind velocity (in
units of 10 km/s) ratio of (3.0-5.1)E-05, with a 5 GHz peak luminosity of
~1.2E+27 erg/s/Hz on day ~464 after explosion. This is consistent with a Type
IIb classification for SN 2010P, making it the most distant and most slowly
evolving Type IIb radio SN detected to date.Comment: 14 pages, 8 tables and 7 figures. Accepted for publication in MNRA
Lepton flavor violating Higgs boson decays from massive seesaw neutrinos
Lepton flavor violating Higgs boson decays are studied within the context of
seesaw models with Majorana massive neutrinos. Two models are considered: The
SM-seesaw, with the Standard Model Particle content plus three right handed
neutrinos, and the MSSM-seesaw, with the Minimal Supersymmetric Standard Model
particle content plus three right handed neutrinos and their supersymmetric
partners. The widths for these decays are derived from a full one-loop
diagrammatic computation in both models, and they are analyzed numerically in
terms of the seesaw parameters, namely, the Dirac and Majorana mass matrices.
Several possible scenarios for these mass matrices that are compatible with
neutrino data are considered. In the SM-seesaw case, very small branching
ratios are found for all studied scenarios. These ratios are explained as a
consequence of the decoupling behaviour of the heavy right handed neutrinos. In
contrast, in the MSSM-seesaw case, sizeable branching ratios are found for some
of the leptonic flavor violating decays of the MSSM neutral Higgs bosons and
for some choices of the seesaw matrices and MSSM parameters. The relevance of
the two competing sources of lepton flavor changing interactions in the
MSSM-seesaw case is also discussed. The non-decoupling behaviour of the
supersymmetric particles contributing in the loop-diagrams is finally shown.Comment: 44pgs. Version to appear in Phys.Rev.
Imperfect Homoclinic Bifurcations
Experimental observations of an almost symmetric electronic circuit show
complicated sequences of bifurcations. These results are discussed in the light
of a theory of imperfect global bifurcations. It is shown that much of the
dynamics observed in the circuit can be understood by reference to imperfect
homoclinic bifurcations without constructing an explicit mathematical model of
the system.Comment: 8 pages, 11 figures, submitted to PR
Stellar Wind Variations During the X-ray High and Low States of Cygnus X-1
We present results from Hubble Space Telescope UV spectroscopy of the massive
X-ray binary system, HD226868 = Cyg X-1. The spectra were obtained at both
orbital conjunction phases in two separate runs in 2002 and 2003 when the
system was in the X-ray high/soft state. The stellar wind lines suffer large
reductions in strength when the black hole is in the foreground due to the
X-ray ionization of the wind ions. A comparison of HST and archival IUE spectra
shows that similar photoionization effects occur in both the X-ray states. We
constructed model UV wind line profiles assuming that X-ray ionization occurs
everywhere in the wind except the zone where the supergiant blocks the X-ray
flux. The good match between the observed and model profiles indicates that the
wind ionization extends to near to the hemisphere of the supergiant facing the
X-ray source. The H-alpha emission strength is generally lower in the high/soft
state compared to the low/hard state, but the He II 4686 emission is relatively
constant between states. The results suggest that mass transfer in Cyg X-1 is
dominated by a focused wind flow that peaks along the axis joining the stars
and that the stellar wind contribution is shut down by X-ray photoionization
effects. The strong stellar wind from the shadowed side of the supergiant will
stall when Coriolis deflection brings the gas into the region of X-ray
illumination. This stalled gas component may be overtaken by the orbital motion
of the black hole and act to inhibit accretion from the focused wind. The
variations in the strength of the shadow wind component may then lead to
accretion rate changes that ultimately determine the X-ray state.Comment: ApJ, in press, 41 pages, 15 figure
Exact Solutions for Domain Walls in Coupled Complex Ginzburg - Landau Equations
The complex Ginzburg Landau equation (CGLE) is a ubiquitous model for the
evolution of slowly varying wave packets in nonlinear dissipative media. A
front (shock) is a transient layer between a plane-wave state and a zero
background. We report exact solutions for domain walls, i.e., pairs of fronts
with opposite polarities, in a system of two coupled CGLEs, which describe
transient layers between semi-infinite domains occupied by each component in
the absence of the other one. For this purpose, a modified Hirota bilinear
operator, first proposed by Bekki and Nozaki, is employed. A novel
factorization procedure is applied to reduce the intermediate calculations
considerably. The ensuing system of equations for the amplitudes and
frequencies is solved by means of computer-assisted algebra. Exact solutions
for mutually-locked front pairs of opposite polarities, with one or several
free parameters, are thus generated. The signs of the cubic gain/loss, linear
amplification/attenuation, and velocity of the coupled-front complex can be
adjusted in a variety of configurations. Numerical simulations are performed to
study the stability properties of such fronts.Comment: Journal of the Physical Society of Japan, in pres
- …