3,521 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
Superheavy Dark Matter with Discrete Gauge Symmetries
We show that there are discrete gauge symmetries protect naturally heavy X
particles from decaying into the ordinary light particles in the supersymmetric
standard model. This makes the proposal very attractive that the superheavy X
particles constitute a part of the dark matter in the present universe. It is
more interesting that there are a class of discrete gauge symmetries which
naturally accommodate a long-lived unstable X particle. We find that in some
discrete Z_{10} models, for example, a superheavy X particle has lifetime
\tau_X \simeq 10^{11}-10^{26} years for its mass M_X \simeq 10^{13}-10^{14}
GeV. This long lifetime is guaranteed by the absence of lower dimensional
operators (of light particles) couple to the X. We briefly discuss a possible
explanation for the recently observed ultra-high-energy cosmic ray events by
the decay of this unstable X particle.Comment: 9 pages, Late
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
A U(3)_C X U(3)_L X U(3)_R gauge symmetry from intersecting D-branes
A three-family non-supersymmetric model with U(3)^3 gauge symmetry is
analyzed in the context of intersecting D-branes. This is equivalent to the
`trinification' model extended by three U(1) factors which survive as global
symmetries in the low energy effective model. The Standard Model fermions are
accommodated in the three possible bifundamental multiplets represented by
strings with endpoints attached on different brane-stacks of this particular
setup. Further, a natural Quark-Lepton hierarchy is realized due to the
existence of the additional abelian symmetriesComment: 10 page
Volume preserving multidimensional integrable systems and Nambu--Poisson geometry
In this paper we study generalized classes of volume preserving
multidimensional integrable systems via Nambu--Poisson mechanics. These
integrable systems belong to the same class of dispersionless KP type equation.
Hence they bear a close resemblance to the self dual Einstein equation. All
these dispersionless KP and dToda type equations can be studied via twistor
geometry, by using the method of Gindikin's pencil of two forms. Following this
approach we study the twistor construction of our volume preserving systems
Relaxed fine-tuning in models with non-universal gaugino masses
We study, in a bottom-up approach, the fine-tuning problem between soft SUSY
breaking parameters and the -term for the successful electroweak symmetry
breaking in the minimal supersymmetric standard model. It is shown that certain
nontrivial ratios between gaugino masses, that is non-universal gaugino masses,
are necessary at the GUT scale, in order for the fine-tuning to be reduced
above 10 % order. In addition, when all the gaugino masses should be regarded
as independent ones in their origins, a small gluino mass
GeV and a non-vanishing -term associated to top squarks
are also required at the GUT scale as well as the non-universality. On the
other hand, when we consider some UV theory, which fixes ratios of soft SUSY
breaking parameters as certain values with the overall magnitude, heavier
spectra are allowed. It is favored that the gluino and wino masses are almost
degenerate at the weak scale, while wider region of bino mass is favorable.Comment: 17 pages, 29 figure
Slepton pair production in e+e- collision in supersymmetric left-right model
The pair production of sleptons in electron-positron collisions is
investigated in a supersymmetric left-right model. The cross section is found
considerably larger than in the minimal supersymmetric version of the Standard
Model (MSSM) because of more contributing graphs. A novel process is a doubly
charged higgsino exchange in u-channel, which makes the angular distribution of
the final state particles and the final state asymmetries to differ from those
of the MSSM. It also allows for the flavour non-diagonal final states , and , forbidden in the
MSSM. These processes also give indirect information about neutrino mixings
since they depend on the same couplings as the Majorana mass terms of the
right-handed neutrinos.Comment: 13 pages + 4figures available upon request, HU-SEFT R 1993-1
Vibrational signature of broken chemical order in a GeS2 glass: a molecular dynamics simulation
Using density functional molecular dynamics simulations, we analyze the
broken chemical order in a GeS glass and its impact on the dynamical
properties of the glass through the in-depth study of the vibrational
eigenvectors. We find homopolar bonds and the frequencies of the corresponding
modes are in agreement with experimental data. Localized S-S modes and 3-fold
coordinated sulfur atoms are found to be at the origin of specific Raman peaks
whose origin was not previously clear. Through the ring size statistics we
find, during the glass formation, a conversion of 3-membered rings into larger
units but also into 2-membered rings whose vibrational signature is in
agreement with experiments.Comment: 11 pages, 8 figures; to appear in Phys. Rev.
Gamification techniques for raising cyber security awareness
Due to the prevalence of online services in modern society, such as internet banking and social media, it is important for users to have an understanding of basic security measures in order to keep themselves safe online. However, users often do not know how to make their online interactions secure, which demonstrates an educational need in this area. Gamification has grown in popularity in recent years and has been used to teach people about a range of subjects. This paper presents an exploratory study investigating the use of gamification techniques to educate average users about password security, with the aim of raising overall security awareness. To explore the impact of such techniques, a role-playing quiz application (RPG) was developed for the Android platform to educate users about password security. Results gained from the work highlightedthat users enjoyed learning via the use of the password application, and felt they benefitted from the inclusion of gamification techniques. Future work seeks to expand the prototype into a full solution, covering a range of security awareness issues
Gravitational lensing by stars with angular momentum
Gravitational lensing by spinning stars, approximated as homogeneous spheres,
is discussed in the weak field limit. Dragging of inertial frames, induced by
angular momentum of the deflector, breaks spherical symmetry. I examine how the
gravito-magnetic field affects image positions, caustics and critical curves.
Distortion in microlensing-induced light curves is also considered.Comment: 9 pages, 9 figures; to appear in MNRA
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