38 research outputs found
Higher Derivative Operators from Scherk-Schwarz Supersymmetry Breaking on T^2/Z_2
In orbifold compactifications on T^2/Z_2 with Scherk-Schwarz supersymmetry
breaking, it is shown that (brane-localised) superpotential interactions and
(bulk) gauge interactions generate at one-loop higher derivative counterterms
to the mass of the brane (or zero-mode of the bulk) scalar field. These
brane-localised operators are generated by integrating out the bulk modes of
the initial theory which, although supersymmetric, is nevertheless
non-renormalisable. It is argued that such operators, of non-perturbative
origin and not protected by non-renormalisation theorems, are generic in
orbifold compactifications and play a crucial role in the UV behaviour of the
two-point Green function of the scalar field self-energy. Their presence in the
action with unknown coefficients prevents one from making predictions about
physics at (momentum) scales close to/above the compactification scale(s). Our
results extend to the case of two dimensional orbifolds, previous findings for
S^1/Z_2 and S^1/(Z_2 x Z_2') compactifications where brane-localised higher
derivative operators are also dynamically generated at loop level, regardless
of the details of the supersymmetry breaking mechanism. We stress the
importance of these operators for the hierarchy and the cosmological constant
problems in compactified theories.Comment: 23 pages, LaTeX, one figure, published version in JHE
Higher Derivative Operators from Transmission of Supersymmetry Breaking on S_1/Z_2
We discuss the role that higher derivative operators play in field theory
orbifold compactifications on S_1/Z_2 with local and non-local (Scherk-Schwarz)
breaking of supersymmetry. Integrating out the bulk fields generates
brane-localised higher derivative counterterms to the mass of the brane (or
zero-mode of the bulk) scalar field, identified with the Higgs field in many
realistic models. Both Yukawa and gauge interactions are considered and the
one-loop results found can be used to study the ``running'' of the scalar field
mass with respect to the momentum scale in 5D orbifolds. In particular this
allows the study of the behaviour of the mass under UV scaling of the momentum.
The relation between supersymmetry breaking and the presence of higher
derivative counterterms to the mass of the scalar field is investigated. This
shows that, regardless of the breaking mechanism, (initial) supersymmetry
cannot, in general, prevent the emergence of such operators. Some implications
for phenomenology of the higher derivative operators are also presented.Comment: 29 pages, LaTeX. Added Section 4 ("Phenomenological implications:
living with ghosts?") and Appendix
Breaking the electroweak symmetry and supersymmetry by a compact extra dimension
We revisit in some more detail a recent specific proposal for the breaking of
the electroweak symmetry and of supersymmetry by a compact extra dimension.
Possible mass terms for the Higgs and the matter hypermultiplets are considered
and their effects on the spectrum analyzed. Previous conclusions are reinforced
and put on firmer ground.Comment: 25 pages, LaTeX, 9 eps figure
Ab initio density functional investigation of B_24 cluster: Rings, Tubes, Planes, and Cages
We investigate the equilibrium geometries and the systematics of bonding in
various isomers of a 24-atom boron cluster using Born-Oppenheimer molecular
dynamics within the framework of density functional theory. The isomers studied
are the rings, the convex and the quasiplanar structures, the tubes and, the
closed structures. A staggered double-ring is found to be the most stable
structure amongst the isomers studied. Our calculations reveal that a 24-atom
boron cluster does form closed 3-d structures. All isomers show staggered
arrangement of nearest neighbor atoms. Such a staggering facilitates
hybridization in boron cluster. A polarization of bonds between the peripheral
atoms in the ring and the planar isomers is also seen. Finally, we discuss the
fusion of two boron icosahedra. We find that the fusion occurs when the
distance between the two icosahedra is less than a critical distance of about
6.5a.u.Comment: 8 pages, 9 figures in jpeg format Editorially approved for
publication in Phys. Rev.
Strongly Coupled Grand Unification in Higher Dimensions
We consider the scenario where all the couplings in the theory are strong at
the cut-off scale, in the context of higher dimensional grand unified field
theories where the unified gauge symmetry is broken by an orbifold
compactification. In this scenario, the non-calculable correction to gauge
unification from unknown ultraviolet physics is naturally suppressed by the
large volume of the extra dimension, and the threshold correction is dominated
by a calculable contribution from Kaluza-Klein towers that gives the values for
\sin^2\theta_w and \alpha_s in good agreement with low-energy data. The
threshold correction is reliably estimated despite the fact that the theory is
strongly coupled at the cut-off scale. A realistic 5d supersymmetric SU(5)
model is presented as an example, where rapid d=6 proton decay is avoided by
putting the first generation matter in the 5d bulk.Comment: 17 pages, latex, to appear in Phys. Rev.
Neutralino relic density in supersymmetric GUTs with no-scale boundary conditions above the unification scale
We investigate SU(5) and SO(10) GUTs with vanishing scalar masses and
trilinear scalar couplings at a scale higher than the unification scale. The
parameter space of the models, further constrained by b-\tau Yukawa coupling
unification, consists of a common gaugino mass and of \tan\beta. We analyze the
low energy phenomenology, finding that A-pole annihilations of neutralinos
and/or coannihilations with the lightest stau drive the relic density within
the cosmologically preferred range in a significant region of the allowed
parameter space. Implications for neutralino direct detection and for CERN LHC
experiments are also discussed.Comment: 14 pages, 5 figures, JHEP style. Version accepted for publication in
JHE
Yukawa coupling unification and non-universal gaugino mediation of supersymmetry breaking
The requirement of Yukawa coupling unification highly constrains the SUSY
parameter space. In several SUSY breaking scenarios it is hard to reconcile
Yukawa coupling unification with experimental constraints from B(b->s gamma)
and the muon anomalous magnetic moment a_mu. We show that b-tau or even t-b-tau
Yukawa unification can be satisfied simultaneously with b->s gamma and a_mu in
the non-universal gaugino mediation scenario. Non-universal gaugino masses
naturally appear in higher dimensional grand unified models in which gauge
symmetry is broken by orbifold compactification. Relations between SUSY
contributions to fermion masses, b->s gamma and a_mu which are typical for
models with universal gaugino masses are relaxed. Consequently, these
phenomenological constraints can be satisfied simultaneously with a relatively
light SUSY spectrum, compared to models with universal gaugino masses.Comment: 20 pages, 8 figures. References added. A copy of the paper with
better resolution figures can be found at
http://www.hep.fsu.edu/~balazs/Physics/Papers/2003
Non-thermal dark matter via Affleck-Dine baryogenesis and its detection possibility
The formation and late time decays of Q-balls are generic consequences of the
Affleck-Dine (AD) baryogenesis. A substantial amount of the lightest
supersymmetry (SUSY) particles (LSPs) are produced non-thermally as the decay
products of these Q-balls. This requires a significantly large annihilation
cross section of the LSP so as not to overclose the universe, which predicts a
higgsino- or wino-like LSP instead of the standard bino LSP. We have reexamined
the AD baryogenesis with special attention to the late-time decays of the
Q-balls, and then specified the parameter regions where the LSPs produced by
the Q-ball decays result in a cosmologically interesting mass density of dark
matter by adopting several SUSY breaking models. This reveals new
cosmologically interesting parameter regions, which have not attracted much
attention so far. We have also investigated the prospects of direct and
indirect detection of these dark matter candidates, and found that there is an
intriguing possibility to detect them in various next generation dark matter
searches.Comment: 51 pages, 18 figures, version accepted for publication in Physical
Review
Large expert-curated database for benchmarking document similarity detection in biomedical literature search
Document recommendation systems for locating relevant literature have mostly relied on methods developed a decade ago. This is largely due to the lack of a large offline gold-standard benchmark of relevant documents that cover a variety of research fields such that newly developed literature search techniques can be compared, improved and translated into practice. To overcome this bottleneck, we have established the RElevant LIterature SearcH consortium consisting of more than 1500 scientists from 84 countries, who have collectively annotated the relevance of over 180 000 PubMed-listed articles with regard to their respective seed (input) article/s. The majority of annotations were contributed by highly experienced, original authors of the seed articles. The collected data cover 76% of all unique PubMed Medical Subject Headings descriptors. No systematic biases were observed across different experience levels, research fields or time spent on annotations. More importantly, annotations of the same document pairs contributed by different scientists were highly concordant. We further show that the three representative baseline methods used to generate recommended articles for evaluation (Okapi Best Matching 25, Term Frequency-Inverse Document Frequency and PubMed Related Articles) had similar overall performances. Additionally, we found that these methods each tend to produce distinct collections of recommended articles, suggesting that a hybrid method may be required to completely capture all relevant articles. The established database server located at https://relishdb.ict.griffith.edu.au is freely available for the downloading of annotation data and the blind testing of new methods. We expect that this benchmark will be useful for stimulating the development of new powerful techniques for title and title/abstract-based search engines for relevant articles in biomedical research.Peer reviewe