4,768 research outputs found
Instanton induced charged fermion and neutrino masses in a minimal Standard Model scenario from intersecting D-branes
String instanton Yukawa corrections from Euclidean D-branes are investigated
in an effective Standard Model theory obtained from the minimal U(3)xU(2)xU(1)
D-brane configuration. In the case of the minimal chiral and Higgs spectrum, it
is found that superpotential contributions are induced by string instantons for
the perturbatively forbidden entries of the up and down quark mass matrices.
Analogous non-perturbative effects generate heavy Majorana neutrino masses and
a Dirac neutrino texture with factorizable Yukawa couplings. For this latter
case, a specific example is worked out where it is shown how this texture can
reconcile the neutrino data.Comment: 17 pages, 3 figure
Neutrino Masses and Mixings from String Theory Instantons
We study possible patterns of neutrino masses and mixings in string models in
which Majorana neutrino masses are generated by a certain class of string
theory instantons recently considered in the literature. These instantons may
generate either directly the dim=5 Weinberg operator or right-handed neutrino
Majorana masses, both with a certain flavour-factorised form. A hierarchy of
neutrino masses naturally appears from the exponentially suppressed
contributions of different instantons. The flavour structure is controlled by
string amplitudes involving neutrino fields and charged instanton zero modes.
For some simple choices for these amplitudes one finds neutrino mixing patterns
consistent with experimental results. In particular, we find that a
tri-bimaximal mixing pattern is obtained for simple symmetric values of the
string correlators.Comment: 24 pages, 2 figure
Fine tuning as an indication of physics beyond the MSSM
We investigate the amount of fine tuning of the electroweak scale in the
presence of new physics beyond the MSSM, parametrized by higher dimensional
operators. We show that these significantly reduce the MSSM fine tuning to
Delta<10 for a Higgs mass between the LEPII bound and 130 GeV, and a
corresponding scale M_* of new physics as high as 30 to 65 times the Higgsino
mass. If the fine-tuning criterion is indeed of physical relevance, the
findings indicate the presence of new physics in the form of new states of mass
of O(M_*) that generated the effective operators in the first instance. At
small these states can be a gauge singlet or a SU(2) triplet. We
derive analytical results for the EW scale fine-tuning for the MSSM with higher
dimensional operators, including the quantum corrections which are also
applicable to the pure MSSM case in the limit the coefficients of the higher
dimension operators vanish. A general expression for the fine-tuning is also
obtained for an arbitrary two-Higgs doublet potential.Comment: 27 pages, 6 Figures; Eqs.(15)-(18) and (A.2)-(A.5) simplified;
figures 1-3 update
Background Symmetries In Orbifolds With Discrete Wilson Lines
Target space symmetries are studied for orbifold compactified string theories
containing Wilson line background fields. The symmetries determined are for
those moduli which contribute to the string loop threshold corrections of the
gauge coupling constants. The groups found are subgroups of the modular group
and depend on the choice of discrete Wilson lines and the shape of
the underlying six-dimensional lattice.Comment: 31 pages, QMW--TH--94/0
Securitization and Lending Standards: Evidence from the Wholesale Loan Market
securitization;bank risk taking;syndicated loans;financial crisis
Radiative B-L symmetry breaking in supersymmetric models
We propose a scheme where the three relevant physics scales related to the
supersymmetry, electroweak, and baryon minus lepton (B-L) breakings are linked
together and occur at the TeV scale. The phenomenological implications in the
Higgs and leptonic sectors are discussed.Comment: 4 page
Using Paper Theatres as an Expressive Arts Therapy Method: Activating Imaginal Worlds in Community Arts Practice
Paper theatres are an artistic form that became widely popular in 19th century Europe. Also known as toy theatre and model theatre, a paper theatre has a small build-your-own proscenium and pre-cut paper characters that can be manipulated. Different styles of paper theatre can be found in several cultures.
In contemporary art, the use of paper theatres in several modalities led to an exploration of whether such theatres also could be used as an art therapy method. Research was conducted into expressive art therapy principles, Jungian perspectives, and recent studies in neurosciences. The studies included in the literature review confirmed that the 2020-21 covid-19 pandemic was having a major impact on the mental health of the adult population. That led to two arts-based group research projects online, and one arts-based heuristic exploration. The initial therapies were implemented online due to the COVID-19 crisis.
The outcome of this research and investigation found that art therapies involving paper theatre—implemented with a therapeutic structure and rationale—can be an expressive art therapy method suitable for community-based and individual interventions.
Future research on paper theatres as a therapeutic method could focus on different populations, in-person (not online) methods, and a longer therapeutic plan of some eight weeks
Magneto-Acoustic Waves of Small Amplitude in Optically Thin Quasi-Isentropic Plasmas
The evolution of quasi-isentropic magnetohydrodynamic waves of small but
finite amplitude in an optically thin plasma is analyzed. The plasma is assumed
to be initially homogeneous, in thermal equilibrium and with a straight and
homogeneous magnetic field frozen in. Depending on the particular form of the
heating/cooling function, the plasma may act as a dissipative or active medium
for magnetoacoustic waves, while Alfven waves are not directly affected. An
evolutionary equation for fast and slow magnetoacoustic waves in the single
wave limit, has been derived and solved, allowing us to analyse the wave
modification by competition of weakly nonlinear and quasi-isentropic effects.
It was shown that the sign of the quasi-isentropic term determines the scenario
of the evolution, either dissipative or active. In the dissipative case, when
the plasma is first order isentropically stable the magnetoacoustic waves are
damped and the time for shock wave formation is delayed. However, in the active
case when the plasma is isentropically overstable, the wave amplitude grows,
the strength of the shock increases and the breaking time decreases. The
magnitude of the above effects depends upon the angle between the wave vector
and the magnetic field. For hot (T > 10^4 K) atomic plasmas with solar
abundances either in the interstellar medium or in the solar atmosphere, as
well as for the cold (T < 10^3 K) ISM molecular gas, the range of temperature
where the plasma is isentropically unstable and the corresponding time and
length-scale for wave breaking have been found.Comment: 14 pages, 10 figures. To appear in ApJ January 200
Numerical evolution of matter in dynamical axisymmetric black hole spacetimes. I. Methods and tests
We have developed a numerical code to study the evolution of self-gravitating
matter in dynamic black hole axisymmetric spacetimes in general relativity. The
matter fields are evolved with a high-resolution shock-capturing scheme that
uses the characteristic information of the general relativistic hydrodynamic
equations to build up a linearized Riemann solver. The spacetime is evolved
with an axisymmetric ADM code designed to evolve a wormhole in full general
relativity. We discuss the numerical and algorithmic issues related to the
effective coupling of the hydrodynamical and spacetime pieces of the code, as
well as the numerical methods and gauge conditions we use to evolve such
spacetimes. The code has been put through a series of tests that verify that it
functions correctly. Particularly, we develop and describe a new set of testbed
calculations and techniques designed to handle dynamically sliced,
self-gravitating matter flows on black holes, and subject the code to these
tests. We make some studies of the spherical and axisymmetric accretion onto a
dynamic black hole, the fully dynamical evolution of imploding shells of dust
with a black hole, the evolution of matter in rotating spacetimes, the
gravitational radiation induced by the presence of the matter fields and the
behavior of apparent horizons through the evolution.Comment: 42 pages, 20 figures, submitted to Phys Rev
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