360 research outputs found
Phenomenological analysis of D-brane Pati-Salam vacua
In the present work we perform a phenomenological analysis of the effective
low energy models with Pati-Salam (PS) gauge symmetry derived in the context of
D-branes. A main issue in these models arises from the fact that the
right-handed fermions and the PS-symmetry breaking Higgs field transform
identically under the PS symmetry, causing unnatural matter-Higgs mixing
effects. We argue that this problem could be solved in particular D-brane
setups where these fields arise in different intersections. We further observe
that whenever a large Higgs mass term is generated in a particular class of
mass spectra, a splitting mechanism -reminiscent of the doublet triplet
splitting- may protect the neutral Higgs components from a heavy mass term. We
analyze the implications of each individual representation which in principle
is available in these models in order to specify the minimal spectrum required
to build up a consistent PS model which reconciles the low energy data. A short
discussion is devoted on the effects of stringy instanton corrections,
particularly those generating missing Yukawa couplings and contributing to the
fermion mass textures. We discuss the correlations of the intersecting D-brane
spectra with those obtained from Gepner constructions and analyze the
superpotential, the resulting mass textures and the low energy implications of
some examples of the latter along the lines proposed above.Comment: 50 pages, 3 figures (v2 - Minor corrections
SU(5) D-brane realizations, Yukawa couplings and proton stability
We discuss SU(5) Grand Unified Theories in the context of orientifold
compactifications. Specifically, we investigate two and three D-brane stack
realizations of the Georgi-Glashow and the flipped SU(5) model and analyze them
with respect to their Yukawa couplings. As pointed out in arXiv:0909.0271 the
most economical Georgi-Glashow realization based on two stacks generically
suffers from a disastrous large proton decay rate. We show that allowing for an
additional U(1) D-brane stack this as well as other phenomenological problems
can be resolved. We exemplify with globally consistent Georgi-Glashow models
based on RCFT that these D-brane quivers can be indeed embedded in a global
setting. These globally consistent realizations admit rigid O(1) instantons
inducing the perturbatively missing coupling 10105^H. Finally we show that
flipped SU(5) D-brane realizations even with multiple U(1) D-brane stacks are
plagued by severe phenomenological drawbacks which generically cannot be
overcome.Comment: 34 pages v2 minor correction
St\"uckelino Dark Matter in Anomalous U(1)' Models
We study a possible dark matter candidate in the framework of a minimal
anomalous extension of the MSSM. It turns out that in a suitable
decoupling limit the St\"uckelino, the fermionic degree of freedom of the
St\"uckelberg multiplet, is the lightest supersymmetric particle (LSP). We
compute the relic density of this particle including coannihilations with the
next to lightest supersymmetric particle (NLSP) and with the next to next to
lightest supersymmetric particle (NNLSP) which are assumed almost degenerate in
mass. This assumption is needed in order to satisfy the stringent limits that
the Wilkinson Microwave Anisotropy Probe (WMAP) puts on the relic density. We
find that the WMAP constraints can be satisifed by different NLSP and NNLSP
configurations as a function of the mass gap with the LSP. These results hold
in the parameter space region where the model remains perturbative.Comment: 21 pages, 6 figures, improved section 5, revised version published on
EPJ
Monopoly power of the medical school market and high incomes of U.S. physicians
We expect the incomes of physicians to remain high in the next decades. Using the latest published physician income data (2015) we calculated the weighted median income of U.S. physicians and the net present value (NPV) of an investment in physician education.
We estimated the NPV assuming that the physicians training began in 2007 and their practice would commence in 2015. We estimated the NPV of the lifetime earnings of a physician based on the median income of all physicians in the sample to be between 7.3 million.
This finding of high NPV’s is consistent with almost all earlier studies of this kind. Physicians continue to experience relatively high incomes and very slow increases in the number of new graduates. We expect an excess demand for positions in medical colleges to continue.
Our findings with respect to the incomes of non-primary physicians (surgeons, radiologist and cardiologists), indicate will continue to be much higher than those of primary physicians.
There are strong evidence suggesting this is because of blockages in physician residency openings in these non-primary fields of medicine.peer-reviewe
Anomalies, Anomalous U(1)'s and generalized Chern-Simons terms
A detailed analysis of anomalous U(1)'s and their effective couplings is
performed both in field theory and string theory. It is motivated by the
possible relevance of such couplings in particle physics, as well as a
potential signal distinguishing string theory from other UV options. The most
general anomaly related effective action is analyzed and parameterized. It
contains Stuckelberg, axionic and Chern-Simons-like couplings. It is shown that
such couplings are generically non-trivial in orientifold string vacua and are
not in general fixed by anomalies. A similar analysis in quantum field theories
provides similar couplings. The trilinear gauge boson couplings are also
calculated and their phenomenological relevance is advocated. We do not find
qualitative differences between string and field theory in this sector.Comment: 52 pages, 2 eps figures, LaTeX, feynmf & youngtab packages (v2 -
Minor corrections, references added
D-brane Instantons on the T^6/Z_3 orientifold
We give a detailed microscopic derivation of gauge and stringy instanton
generated superpotentials for gauge theories living on D3-branes at
Z_3-orientifold singularities. Gauge instantons are generated by D(-1)-branes
and lead to Affleck, Dine and Seiberg (ADS) like superpotentials in the
effective N=1 gauge theories with three generations of bifundamental and
anti/symmetric matter. Stringy instanton effects are generated by Euclidean
ED3-branes wrapping four-cycles on T^6/\Z_3. They give rise to Majorana masses
in one case and non-renormalizable superpotentials for the other cases. Finally
we determine the conditions under which ADS like superpotentials are generated
in N=1 gauge theories with adjoints, fundamentals, symmetric and antisymmetric
chiral matter.Comment: 31 pages, no figure
Unification and fermion mass relations in low string scale D-brane models
In this talk, gauge coupling evolution is analyzed in D-brane inspired models
with two Higgs doublets and a U(3)xU(2)xU(1)^N gauge symmetry. In particular,
we focus on D-brane configurations with two or three abelian factors. We find
that the correct hypercharge assignment of the Standard Model particles is
reproduced for six viable models distinguished by different brane
configurations. We also investigate the bottom tau quark mass relation and find
that the correct low energy m_b / m_\tau ratio is obtained for equal b-\tau
Yukawa couplings at a string scale around 10^3 TeV.Comment: 10 pages, 3 figures. Talk presented at the ``Corfu Summer
Institute'', Corfu-Greece, September 4-14, 2005. To appear in the proceedings
of RTN workshop on the Quest for Unification Theory Confronts Experimen
Understanding the Political Ideology of Legislators from Social Media Images
In this paper, we seek to understand how politicians use images to express
ideological rhetoric through Facebook images posted by members of the U.S.
House and Senate. In the era of social media, politics has become saturated
with imagery, a potent and emotionally salient form of political rhetoric which
has been used by politicians and political organizations to influence public
sentiment and voting behavior for well over a century. To date, however, little
is known about how images are used as political rhetoric. Using deep learning
techniques to automatically predict Republican or Democratic party affiliation
solely from the Facebook photographs of the members of the 114th U.S. Congress,
we demonstrate that predicted class probabilities from our model function as an
accurate proxy of the political ideology of images along a left-right
(liberal-conservative) dimension. After controlling for the gender and race of
politicians, our method achieves an accuracy of 59.28% from single photographs
and 82.35% when aggregating scores from multiple photographs (up to 150) of the
same person. To better understand image content distinguishing liberal from
conservative images, we also perform in-depth content analyses of the
photographs. Our findings suggest that conservatives tend to use more images
supporting status quo political institutions and hierarchy maintenance,
featuring individuals from dominant social groups, and displaying greater
happiness than liberals.Comment: To appear in the Proceedings of International AAAI Conference on Web
and Social Media (ICWSM 2020
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