2,374 research outputs found
Region of hadron-quark mixed phase in hybrid stars
Hadron--quark mixed phase is expected in a wide region of the inner structure
of hybrid stars. However, we show that the hadron--quark mixed phase should be
restricted to a narrower region to because of the charge screening effect. The
narrow region of the mixed phase seems to explain physical phenomena of neutron
stars such as the strong magnetic field and glitch phenomena, and it would give
a new cooling curve for the neutron star.Comment: to be published in Physical Review
Higgs Mass from D-Terms: a Litmus Test
We explore supersymmetric theories in which the Higgs mass is boosted by the
non-decoupling D-terms of an extended gauge symmetry, defined here to
be a general linear combination of hypercharge, baryon number, and lepton
number. Crucially, the gauge coupling, , is bounded from below to
accommodate the Higgs mass, while the quarks and leptons are required by gauge
invariance to carry non-zero charge under . This induces an irreducible
rate, BR, for relevant to
existing and future resonance searches, and gives rise to higher dimension
operators that are stringently constrained by precision electroweak
measurements. Combined, these bounds define a maximally allowed region in the
space of observables, (BR, ), outside of which is excluded by
naturalness and experimental limits. If natural supersymmetry utilizes
non-decoupling D-terms, then the associated boson can only be observed
within this window, providing a model independent `litmus test' for this broad
class of scenarios at the LHC. Comparing limits, we find that current LHC
results only exclude regions in parameter space which were already disfavored
by precision electroweak data.Comment: 7 pages, 9 figure
Orbital phase spectroscopy of X-ray pulsars to study the stellar wind of the companion
High Mass X-ray Binary Pulsars (HMXBP), in which the companion star is a
source of supersonic stellar wind, provide a laboratory to probe the velocity
and density profile of such winds. Here, we have measured the variation of the
absorption column density along with other spectral parameters over the binary
orbit for two HMXBP in elliptical orbits, as observed with the Rossi X-ray
Timing Explorer (RXTE) and the BeppoSAX satellites. A spherically symmetric
wind profile was used as a model to compare the observed column density
variations. In 4U 1538-52, we find the model corroborating the observations;
whereas in GX 301-2, the stellar wind appears to be very clumpy and a smooth
symmetric wind model seems to be inadequate in explaining the variation in
column density.Comment: 4 pages, 4 figures. To be Published in Elsevier/AS
Orbital Phase Spectroscopy of GX 301--2 with RXTE-PCA
We have investigated the orbital phase dependence of the X-ray spectrum of
the High Mass X-ray Binary pulsar GX 301--2. Here we present the results from a
spectral analysis of two sets of observations of GX 301--2 with the Rossi X-ray
Timing Explorer (RXTE). Of particular interest are the variations of the
absorption column density and the iron line flux along with other parameters of
the spectral model with the orbital phase. We found that the X-ray spectrum can
almost always be fitted with a partial covering absorption model. We have
detected enhanced absorption near the periastron. However, the column density
variation with orbital phase is not smooth, as is expected in a smooth stellar
wind model. We discuss the results of the column density variation in the light
of the two proposed models for GX 301-2, an equatorial disk emanating from the
companion star Wray 977 and a gas stream following the neutron star. We also
found that the iron K_alpha and K_beta line fluxes have peaks near the
periastron and are well correlated with the continuum hard X-ray flux. The line
equivalent width shows an interesting pattern with the column density,
reasonably constant for low values of the column density and increasing rapidly
beyond a certain value.Comment: 15 pages, 7 figures. accepted in Astronomy and Astrophysic
TeV scale mirage mediation in NMSSM
We study the next-to-minimal supersymmetric standard model. We consider soft
supersymmetry breaking parameters, which are induced by the mirage mediation
mechanism of supersymmetry breaking. We concentrate on the mirage mediation,
where the so-called mirage scale is the TeV scale. In this scenario, we can
realize the up-type Higgs soft mass of O(200) GeV, while other masses such as
gaugino masses and stop masses are heavy such as 1 TeV or more. Cancellation
between the effective \mu-term and the down-type Higgs soft mass ameliorates
the fine-tuning in the electroweak symmetry breaking even for \mu=O(500) GeV.
The mixing between the doublet and singlet Higgs bosons is suppressed by
(\lambda/\kappa)/tan\beta. Then the lightest doublet Higgs mass naturally
reaches 125 GeV lifted by the new quartic coupling. The higgsino and singlino
are light and their linear combination is the lightest superparticle.Comment: 24 pages, 24 figures, Numerical analysis is replaced with the version
calculated by NMSSMTools. Comments and references are added on the suppressed
doublet-singlet mixing and cases in which the 125 GeV boson is the 2nd
lightest CP-even scalar. The version accepted by JHE
Higgs Boson Mass in Low Scale Gauge Mediation Models
We consider low scale gauge mediation models with a very light gravitino
m_{3/2}~16 eV, in the light of recent experimental hints on the Higgs boson
mass. The light gravitino is very interesting since there is no gravitino
over-production problem, but it seems difficult to explain the Higgs boson mass
of ~125 GeV. This is because of the conflict between the light gravitino mass
and heavy SUSY particle masses needed for producing the relatively heavy Higgs
boson mass. We consider two possible extensions in this paper: a singlet
extension of the Higgs sector, and strongly coupled gauge mediation. We show
that there is a large parameter space, in both scenarios, where the Higgs boson
mass of ~125 GeV is explained without any conflict with such a very light
gravitino.Comment: 23 pages, 5 figure
Phenomenological Aspects of Gauge Mediation with Sequestered Supersymmetry Breaking in light of Dark Matter Detection
In a recent work, a model of gauge mediation with sequestered supersymmetry
(SUSY) breaking was proposed. In this model, the mass of the gravitino is
O(100) GeV without causing the flavor-changing neutral-current problem. In
contrast to traditional gauge mediation, the gravitino is not the lightest SUSY
particle and the neutralino is the candidate of the dark matter. In this paper,
we investigate phenomenological aspects of this model and discuss the
possibility of the direct detection of the dark matter. In particular, we focus
on the light neutralino case and find that the light-Higgsino scenario such as
the focus point is interesting, taking account of the recent CDMS result.Comment: 17 pages, 8 figures; v2:references added, some corrections;
v3:version accepted for publication in JHE
Quasi periodic oscillations in XTE J0111.2--7317, highest frequency among the HMXB pulsars
We report here discovery of Quasi Periodic Oscillations (QPOs) in the High
Mass X-ray Binary (HMXB) Pulsar XTE J0111.20-7317 during a transient outburst
in this source in December 1998. Using observations made with the proportional
counter array of the Rossi X-ray Timing Explorer during the second peak and the
declining phase of this outburst we have discovered a QPO feature at a
frequency of 1.27 Hz. We have ruled out the possibility that the observed QPOs
can instead be from the neighbouring bright X-ray pulsar SMC X-1. This is the
highest frequency QPO feature ever detected in any HMXB pulsar. In the absence
of a cyclotron absorption feature in the X-ray spectrum, the QPO feature, along
with the pulse period and X-ray flux measurement measurement helps us to
constrain the magnetic field strength of the neutron star.Comment: Accepted for publication in The Astrophysical Journa
Crystal growth and characterization of MgB2: Relation between structure and superconducting properties
We discuss the important aspects of synthesis and crystal growth of MgB2
under high pressure (P) and temperature (T) in Mg-B-N system, including the
optimisation of P-T conditions for reproducible crystal growth, the role of
liquid phases in this process, the temperature dependence of crystal size and
the effect of growing instabilities on single crystals morphology. Extensive
experiments have been carried out on single crystals with slightly different
lattice constants and defects concentration, which revealed and possible
effects of Mg-deficiency and lattice strain on the superconducting properties
of MgB2 (Tc, Jc, residual resistivity ratio, anisotropy etc.).Comment: 29 pages, 9 figures, 1 table, Proc.of International Workshop on
Superconductivity in Magnesium Diboride and Related Materials "BOROMAG",
17-19 June 2002, Genoa, Italy (submitted to Supercond.Sci and Technol.
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