923 research outputs found
Mersenne Primes, Polygonal Anomalies and String Theory Classification
It is pointed out that the Mersenne primes and associated
perfect numbers play a significant role in string
theory; this observation may suggest a classification of consistent string
theories.Comment: 10 pages LaTe
Hawking radiation in different coordinate settings: Complex paths approach
We apply the technique of complex paths to obtain Hawking radiation in
different coordinate representations of the Schwarzschild space-time. The
coordinate representations we consider do not possess a singularity at the
horizon unlike the standard Schwarzschild coordinate. However, the event
horizon manifests itself as a singularity in the expression for the
semiclassical action. This singularity is regularized by using the method of
complex paths and we find that Hawking radiation is recovered in these
coordinates indicating the covariance of Hawking radiation as far as these
coordinates are concerned.Comment: 18 pages, 2 figures, Uses IOP style file; final version; accepted in
Class. Quant. Gra
Study of the three-dimensional shape and dynamics of coronal loops observed by Hinode/EIS
We study plasma flows along selected coronal loops in NOAA Active Region
10926, observed on 3 December 2006 with Hinode's EUV Imaging Spectrograph
(EIS). From the shape of the loops traced on intensity images and the Doppler
shifts measured along their length we compute their three-dimensional (3D)
shape and plasma flow velocity using a simple geometrical model. This
calculation was performed for loops visible in the Fe VIII 185 Ang., Fe X 184
Ang., Fe XII 195 Ang., Fe XIII 202 Ang., and Fe XV 284 Ang. spectral lines. In
most cases the flow is unidirectional from one footpoint to the other but there
are also cases of draining motions from the top of the loops to their
footpoints. Our results indicate that the same loop may show different flow
patterns when observed in different spectral lines, suggesting a dynamically
complex rather than a monolithic structure. We have also carried out magnetic
extrapolations in the linear force-free field approximation using SOHO/MDI
magnetograms, aiming toward a first-order identification of extrapolated
magnetic field lines corresponding to the reconstructed loops. In all cases,
the best-fit extrapolated lines exhibit left-handed twist (alpha < 0), in
agreement with the dominant twist of the region.Comment: 17 pages, 6 figure
U(2)-like Flavor Symmetries and Approximate Bimaximal Neutrino Mixing
Models involving a U(2) flavor symmetry, or any of a number of its
non-Abelian discrete subgroups, can explain the observed hierarchy of charged
fermion masses and CKM angles. It is known that a large neutrino mixing angle
connecting second and third generation fields may arise via the seesaw
mechanism in these models, without a fine tuning of parameters. Here we show
that it is possible to obtain approximate bimaximal mixing in a class of models
with U(2)-like Yukawa textures. We find a minimal form for Dirac and Majorana
neutrino mass matrices that leads to two large mixing angles, and show that our
result can quantitatively explain atmospheric neutrino oscillations while
accommodating the favored, large angle MSW solution to the solar neutrino
problem. We demonstrate that these textures can arise in models by presenting a
number of explicit examples.Comment: 20 pages RevTex4, 2 figure
Maximal Neutrino Mixing from a Minimal Flavor Symmetry
We study a number of models, based on a non-Abelian discrete group, that
successfully reproduce the simple and predictive Yukawa textures usually
associated with U(2) theories of flavor. These models allow for solutions to
the solar and atmospheric neutrino problems that do not require altering
successful predictions for the charged fermions or introducing sterile
neutrinos. Although Yukawa matrices are hierarchical in the models we consider,
the mixing between second- and third-generation neutrinos is naturally large.
We first present a quantitative analysis of a minimal model proposed in earlier
work, consisting of a global fit to fermion masses and mixing angles, including
the most important renormalization group effects. We then propose two new
variant models: The first reproduces all important features of the SU(5)xU(2)
unified theory with neither SU(5) nor U(2). The second demonstrates that
discrete subgroups of SU(2) can be used in constructing viable supersymmetric
theories of flavor without scalar universality even though SU(2) by itself
cannot.Comment: 34 pages LaTeX, 1 eps figure, minor revisions and references adde
Genetic and phenotypic characterization of indolent T-cell lymphoproliferative disorders of the gastrointestinal tract.
Indolent T-cell lymphoproliferative disorders of the gastrointestinal tract are rare clonal T-cell diseases that more commonly occur in the intestines and have a protracted clinical course. Different immunophenotypic subsets have been described, but the molecular pathogenesis and cell of origin of these lymphocytic proliferations is poorly understood. Hence, we performed targeted next-generation sequencing and comprehensive immunophenotypic analysis of ten indolent T-cell lymphoproliferative disorders of the gastrointestinal tract, which comprised CD4 <sup>+</sup> (n=4), CD8 <sup>+</sup> (n=4), CD4 <sup>+</sup> /CD8 <sup>+</sup> (n=1) and CD4 <sup>-</sup> /CD8 <sup>-</sup> (n=1) cases. Genetic alterations, including recurrent mutations and novel rearrangements, were identified in 8/10 (80%) of these lymphoproliferative disorders. The CD4 <sup>+</sup> , CD4 <sup>+</sup> /CD8 <sup>+</sup> , and CD4 <sup>-</sup> /CD8 <sup>-</sup> cases harbored frequent alterations of JAK-STAT pathway genes (5/6, 82%); STAT3 mutations (n=3), SOCS1 deletion (n=1) and STAT3-JAK2 rearrangement (n=1), and 4/6 (67%) had concomitant mutations in epigenetic modifier genes (TET2, DNMT3A, KMT2D). Conversely, 2/4 (50%) of the CD8 <sup>+</sup> cases exhibited structural alterations involving the 3' untranslated region of the IL2 gene. Longitudinal genetic analysis revealed stable mutational profiles in 4/5 (80%) cases and acquisition of mutations in one case was a harbinger of disease transformation. The CD4 <sup>+</sup> and CD4 <sup>+</sup> /CD8 <sup>+</sup> lymphoproliferative disorders displayed heterogeneous Th1 (T-bet <sup>+</sup> ), Th2 (GATA3 <sup>+</sup> ) or hybrid Th1/Th2 (T-bet <sup>+</sup> /GATA3 <sup>+</sup> ) profiles, while the majority of CD8 <sup>+</sup> disorders and the CD4 <sup>-</sup> /CD8 <sup>-</sup> disease showed a type-2 polarized (GATA3 <sup>+</sup> ) effector T-cell (Tc2) phenotype. Additionally, CD103 expression was noted in 2/4 CD8 <sup>+</sup> cases. Our findings provide insights into the pathogenetic bases of indolent T-cell lymphoproliferative disorders of the gastrointestinal tract and confirm the heterogeneous nature of these diseases. Detection of shared and distinct genetic alterations of the JAK-STAT pathway in certain immunophenotypic subsets warrants further mechanistic studies to determine whether therapeutic targeting of this signaling cascade is efficacious for a proportion of patients with these recalcitrant diseases
Deconfining Phase Transition as a Matrix Model of Renormalized Polyakov Loops
We discuss how to extract renormalized from bare Polyakov loops in SU(N)
lattice gauge theories at nonzero temperature in four spacetime dimensions.
Single loops in an irreducible representation are multiplicatively renormalized
without mixing, through a renormalization constant which depends upon both
representation and temperature. The values of renormalized loops in the four
lowest representations of SU(3) were measured numerically on small, coarse
lattices. We find that in magnitude, condensates for the sextet and octet loops
are approximately the square of the triplet loop. This agrees with a large
expansion, where factorization implies that the expectation values of loops in
adjoint and higher representations are just powers of fundamental and
anti-fundamental loops. For three colors, numerically the corrections to the
large relations are greatest for the sextet loop, ; these
represent corrections of for N=3. The values of the renormalized
triplet loop can be described by an SU(3) matrix model, with an effective
action dominated by the triplet loop. In several ways, the deconfining phase
transition for N=3 appears to be like that in the matrix model of
Gross and Witten.Comment: 24 pages, 7 figures; v2, 27 pages, 12 figures, extended discussion
for clarity, results unchange
New Approach to GUTs
We introduce a new string-inspired approach to the subject of grand
unification which allows the GUT scale to be small, \lesssim 200 TeV, so that
it is within the reach of {\em conceivable} laboratory accelerated colliding
beam devices. The key ingredient is a novel use of the heterotic string
symmetry group physics ideas to render baryon number violating effects small
enough to have escaped detection to date. This part of the approach involves
new unknown parameters to be tested experimentally. A possible hint at the
existence of these new parameters may already exist in the EW precision data
comparisons with the SM expectations.Comment: 8 pages; improved text and references, note added; extended text, 1
figure added; extended text for publication in Eur. Phys. Journal
Tetracritical behavior in strongly interacting theories
We suggest a tetracritical fixed point to naturally occur in strongly
interacting theories. As a fundamental example we analyze the
temperature--quark chemical potential phase diagram of QCD with fermions in the
adjoint representation of the gauge group (i.e. adjoint QCD). Here we show that
such a non trivial multicritical point exists and is due to the interplay
between the spontaneous breaking of a global U(1) symmetry and the center group
symmetry associated to confinement. Our results demonstrate that taking
confinement into account is essential for understanding the critical behavior
as well as the full structure of the phase diagram of adjoint QCD. This is in
contrast to ordinary QCD where the center group symmetry associated to
confinement is explicitly broken when the quarks are part of the theory.Comment: RevTex, 5 figures. Final version to appear in PR
Spallation reactions. A successful interplay between modeling and applications
The spallation reactions are a type of nuclear reaction which occur in space
by interaction of the cosmic rays with interstellar bodies. The first
spallation reactions induced with an accelerator took place in 1947 at the
Berkeley cyclotron (University of California) with 200 MeV deuterons and 400
MeV alpha beams. They highlighted the multiple emission of neutrons and charged
particles and the production of a large number of residual nuclei far different
from the target nuclei. The same year R. Serber describes the reaction in two
steps: a first and fast one with high-energy particle emission leading to an
excited remnant nucleus, and a second one, much slower, the de-excitation of
the remnant. In 2010 IAEA organized a worskhop to present the results of the
most widely used spallation codes within a benchmark of spallation models. If
one of the goals was to understand the deficiencies, if any, in each code, one
remarkable outcome points out the overall high-quality level of some models and
so the great improvements achieved since Serber. Particle transport codes can
then rely on such spallation models to treat the reactions between a light
particle and an atomic nucleus with energies spanning from few tens of MeV up
to some GeV. An overview of the spallation reactions modeling is presented in
order to point out the incomparable contribution of models based on basic
physics to numerous applications where such reactions occur. Validations or
benchmarks, which are necessary steps in the improvement process, are also
addressed, as well as the potential future domains of development. Spallation
reactions modeling is a representative case of continuous studies aiming at
understanding a reaction mechanism and which end up in a powerful tool.Comment: 59 pages, 54 figures, Revie
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