9,023 research outputs found
Dirac Triplet Extension of the MSSM
In this paper we explore extensions of the Minimal Supersymmetric Standard
Model involving two triplet chiral superfields that share a
superpotential Dirac mass yet only one of which couples to the Higgs fields.
This choice is motivated by recent work using two singlet superfields with the
same superpotential requirements. We find that, as in the singlet case, the
Higgs mass in the triplet extension can easily be raised to
without introducing large fine-tuning. For triplets that carry hypercharge, the
regions of least fine tuning are characterized by small contributions to the
parameter, and light stop squarks, ; the latter is a result of the dependence of
the triplet contribution to the Higgs mass. Despite such light stop masses,
these models are viable provided the stop-electroweakino spectrum is
sufficiently compressed.Comment: 26 pages, 4 figure
Staircase to Higher-Order Topological Phase Transitions
We find a series of topological phase transitions of increasing order, beyond
the more standard second-order phase transition in a one-dimensional
topological superconductor. The jumps in the order of the transitions depend on
the range of the pairing interaction, which is parametrized by an algebraic
decay with exponent . Remarkably, in the limit the order
of the topological transition becomes infinite. We compute the critical
exponents for the series of higher-order transitions in exact form and find
that they fulfill the hyperscaling relation. We also study the critical
behaviour at the boundary of the system and discuss potential experimental
platforms of magnetic atoms in superconductors.Comment: 5+5pages, 7 figures. Accepted as a Rapid Communicatio
Multiwavelength analysis of the young open cluster NGC 2362
We present a multiwavelength analysis of the young open cluster NGC 2362.
UBVRcIc CCD photometric observations, together with available data in the
Chandra data base, near infrared data from the Two Micron All Sky Survey
(2MASS), and recently published Halpha spectroscopy were used to get
information about the evolutionary stage of the cluster and the main physical
properties of its stellar content. Cluster membership is estimated for every
individual star by means of ZAMS and isochrone fitting. The cluster is
confirmed to host a richly populated pre-main sequence (PMS), and to contain a
large amount of X-ray emitting stars, which reach from the PMS members of GK
spectral type, up to the most luminous OB type main sequence (MS) members. The
PMS cluster members show no significant age spread, and the comparison to both
PMS and post-MS isochrones suggests a younger age for the more massive MS than
for lower mass PMS members. The analysis allows to asses the validity of
currently used pre-main sequence evolutionary models, and supports the
suggestion of a well defined positive correlation of the X-ray emission from
PMS stars with their bolometric luminosity. Clear differences are found on the
other hand, between the X-ray activity properties of MS and PMS cluster
members, both in the relation between X-ray luminosity and bolometric
luminosity, and in spectral properties as well.Comment: 1 gzipped file: 1 tex file with 9 pages text. 5 ps files with
figures. Submitted to Astrophysical Journa
Quantum simulation of Anderson and Kondo lattices with superconducting qubits
We introduce a mapping between a variety of superconducting circuits and a
family of Hamiltonians describing localized magnetic impurities interacting
with conduction bands. This includes the Anderson model, the single impurity
one- and two-channel Kondo problem, as well as the 1D Kondo lattice. We compare
the requirements for performing quantum simulations using the proposed circuits
to those of universal quantum computation with superconducting qubits, singling
out the specific challenges that will have to be addressed.Comment: Longer versio
VLT and GTC observations of SDSS J0123+00: a type 2 quasar triggered in a galaxy encounter?
We present long-slit spectroscopy, continuum and [OIII]5007 imaging data
obtained with the Very Large Telescope and the Gran Telescopio Canarias of the
type 2 quasar SDSS J0123+00 at z=0.399. The quasar lies in a complex, gas-rich
environment. It appears to be physically connected by a tidal bridge to another
galaxy at a projected distance of ~100 kpc, which suggests this is an
interacting system. Ionized gas is detected to a distance of at least ~133 kpc
from the nucleus. The nebula has a total extension of ~180 kpc. This is one of
the largest ionized nebulae ever detected associated with an active galaxy.
Based on the environmental properties, we propose that the origin of the nebula
is tidal debris from a galactic encounter, which could as well be the
triggering mechanism of the nuclear activity. SDSS J0123+00 demonstrates that
giant, luminous ionized nebulae can exist associated with type 2 quasars of low
radio luminosities, contrary to expectations based on type 1 quasar studies.Comment: 6 pages, 5 figures. Accepted for publication in MNRAS Letter
Starburst radio galaxies: general properties, evolutionary histories and triggering
In this paper we discuss the results of a programme of spectral synthesis
modelling of a sample of starburst radio galaxies in the context of scenarios
for the triggering of the activity and the evolution of the host galaxies. The
starburst radio galaxies -- comprising ~15 - 25% of all powerful extragalactic
radio sources -- frequently show disturbed morphologies at optical wavelengths,
and unusual radio structures, although their stellar masses are typical of
radio galaxies as a class. In terms of the characteristic ages of their young
stellar populations (YSP), the objects can be divided into two groups: those
with YSP ages t_ysp < 0.1 Gyr, in which the radio source has been triggered
quasi-simultaneously with the main starburst episode, and those with older YSP
in which the radio source has been triggered or re-triggered a significant
period after the starburst episode. Combining the information on the YSP with
that on the optical morphologies of the host galaxies, we deduce that the
majority of the starburst radio galaxies have been triggered in galaxy mergers
in which at least one of the galaxies is gas rich. However, the triggering (or
re-triggering) of the radio jets can occur immediately before, around, or a
significant period after the final coalescence of the merging nuclei,
reflecting the complex gas infall histories of the merger events. Overall, our
results provide further evidence that powerful radio jet activity can be
triggered via a variety of mechanisms, including different evolutionary stages
of major galaxy mergers; clearly radio-loud AGN activity is not solely
associated with a particular stage of a unique type of gas accretion event.Comment: 16 pages, 3 Figures, accepted for publication in MNRA
Phase diagram of the anti-ferromagnetic xxz model in the presence of an external magnetic field
The anisotropic s=1/2 anti-ferromagnetic Heisenberg chain in the presence of
an external magnetic field is studied by using the standard quantum
renormalization group. We obtain the critical line of the transition from
partially magnetized (PM) phase to the saturated ferromagnetic (SFM) phase. The
crossover exponent between the PM phase and anti-ferromagnetic Ising (AFI)
phase is evaluated. Our results show that the anisotropy(\d) term is relevant
and causes crossover. These results indicate that the standard RG approach
yields fairly good values for the critical points and their exponents. The
magnetization curve, correlation functions and the ground state energy per site
are obtained and compared with the known exact results.Comment: A LaTex file(20 pages) and 9 PS figure
VIMOS-VLT spectroscopy of the giant Ly-alpha nebulae associated with three z~2.5 radio galaxies
The morphological and spectroscopic properties of the giant (>60 kpc)
Ly-alpha nebulae associated with three radio galaxies at z~2.5 (MRC 1558-003,
MRC 2025-218 and MRC 0140-257) have been investigated using integral field
spectroscopic data obtained with VIMOS on VLT.
The morphologies are varied. The nebula of one source has a centrally peaked,
rounded appearance. In the other two objects, it consists of two spatial
components. The three nebulae are aligned with the radio axis within <30 deg.
The total Ly-alpha luminosities are in the range (0.3-3.4) x 1e44 erg s-1. The
Ly-alpha spectral profile shows strong variation through the nebulae, with FWHM
values in the range ~400-1500 km s-1 and velocity shifts V~120-600 km s-1.
We present an infall model which can explain successfully most Ly-alpha
morphological and spectroscopic properties of the nebula associated with MRC
1558-003. This adds further support to our previous conclusion that the
_quiescent_ giant nebulae associated with this and other high redshift powerful
radio galaxies are in infall. A problem for this model is the difficulty to
reproduce the large Ly-alpha FWHM values.
We have discovered a giant (~85 kpc) Ly-alpha nebula associated with the
radio galaxy MRC 0140-257 at z=2.64. It shows strikingly relaxed kinematics
(FWHM2) radio galaxies.Comment: 14 pages, 13 figures. Accepted for publication in MNRA
Quantum Spins and Quasiperiodicity: a real space renormalization group approach
We study the antiferromagnetic spin-1/2 Heisenberg model on a two-dimensional
bipartite quasiperiodic structure, the octagonal tiling -- the aperiodic
equivalent of the square lattice for periodic systems.
An approximate block spin renormalization scheme is described for this
problem. The ground state energy and local staggered magnetizations for this
system are calculated, and compared with the results of a recent Quantum Monte
Carlo calculation for the tiling. It is conjectured that the ground state
energy is exactly equal to that of the quantum antiferromagnet on the square
lattice.Comment: To appear in Physical Review Letter
Non-relativistic limit in the 2+1 Dirac Oscillator: A Ramsey Interferometry Effect
We study the non-relativistic limit of a paradigmatic model in Relativistic
Quantum Mechanics, the two-dimensional Dirac oscillator. Remarkably, we find a
novel kind of Zitterbewegung which persists in this non-relativistic regime,
and leads to an observable deformation of the particle orbit. This effect can
be interpreted in terms of a Ramsey Interferometric phenomenon, allowing an
insightful connection between Relativistic Quantum Mechanics and Quantum
Optics. Furthermore, subsequent corrections to the non-relativistic limit,
which account for the usual spin-orbit Zitterbewegung, can be neatly understood
in terms of a Mach-Zehnder interferometer.Comment: RevTex4 file, color figures, submitted for publicatio
- …