41,105 research outputs found
Effects of Universal Extra Dimensions on Higgs signals at LHC
A major focus at the Large Hadron Collider (LHC) will be Higgs boson studies
and it would be an interesting prospect to simultaneously probe for physics
beyond the Standard Model (SM) in the Higgs signals. In this work we show as to
what extent, the effects of Universal Extra Dimension (UED) can be isolated at
the LHC through the Higgs signals. By doing a detailed study of the different
uncertainties involved in the measurement of the rates for the process pp --> h
--> gamma gamma we estimate the extent to which these uncertainties can mask
the effects of the contributions coming from UED.Comment: 13 pages, LateX, Title changed, text and figures modified. Version to
appear in IJMP
Hot QCD equations of state and RHIC
We show how hot QCD equations of states can be adapted to make definite
predictions for quark-gluon plasma at RHIC. We consider equations of state up
to and . Our method involves the extraction of
equilibrium distribution functions for gluons and quarks from these equations
of state by capturing the the interaction effects entirely in the effective
chemical potentials. We further utilize these distribution functions to study
the screening length in hot QCD and dissociation phenomenon of heavy quarkonia
states by combining this understanding with the semi-classical transport
theory.Comment: Based on poster presented during quark matter-2008(4-10 Feb 2008)
Jaipur India; 4 Pages, 2 eps fig
Post-spinel transformations and equation of state in ZnGa2O4: Determination at high-pressure by in situ x-ray diffraction
Room temperature angle-dispersive x-ray diffraction measurements on spinel
ZnGa2O4 up to 56 GPa show evidence of two structural phase transformations. At
31.2 GPa, ZnGa2O4 undergoes a transition from the cubic spinel structure to a
tetragonal spinel structure similar to that of ZnMn2O4. At 55 GPa, a second
transition to the orthorhombic marokite structure (CaMn2O4-type) takes place.
The equation of state of cubic spinel ZnGa2O4 is determined: V0 = 580.1(9) A3,
B0 = 233(8) GPa, B0'= 8.3(4), and B0''= -0.1145 GPa-1 (implied value); showing
that ZnGa2O4 is one of the less compressible spinels studied to date. For the
tetragonal structure an equation of state is also determined: V0 = 257.8(9) A3,
B0 = 257(11) GPa, B0'= 7.5(6), and B0''= -0.0764 GPa-1 (implied value). The
reported structural sequence coincides with that found in NiMn2O4 and MgMn2O4.Comment: 20 pages, 4 figures, 2 Table
Graphene Ripples as a Realization of a Two-Dimensional Ising Model: A Scanning Tunneling Microscope Study
Ripples in pristine freestanding graphene naturally orient themselves in an
array that is alternately curved-up and curved-down; maintaining an average
height of zero. Using scanning tunneling microscopy (STM) to apply a local
force, the graphene sheet will reversibly rise and fall in height until the
height reaches 60-70 percent of its maximum at which point a sudden, permanent
jump occurs. We successfully model the ripples as a spin-half Ising magnetic
system, where the height of the graphene is the spin. The permanent jump in
height, controlled by the tunneling current, is found to be equivalent to an
antiferromagnetic-to-ferromagnetic phase transition. The thermal load
underneath the STM tip alters the local tension and is identified as the
responsible mechanism for the phase transition. Four universal critical
exponents are measured from our STM data, and the model provides insight into
the statistical role of graphenes unusual negative thermal expansion
coefficient.Comment: 12 pages, 5 figures, 1 tabl
A study of nuclei of astrophysical interest in the continuum shell model
We present here the first application of realistic shell model (SM) including
coupling between many-particle (quasi-)bound states and the continuum of
one-particle scattering states to the spectroscopy of 8B and to the calculation
of astrophysical factors in the reaction 7Be(p,gamma)8B.Comment: 9 pages incl. 3 figures, LaTeX with iopart class and epsf. Invited
talk at the Int. Workshop on Physics with Radioactive Nuclear Beams, Jan.
12-17, 1998, Puri, India. Shortened version will be published in proceedings
to apear as a separate J. Phys. G volum
Asymmetry to symmetry transition of Fano line-shape: Analytical derivation
An analytical derivation of Fano line-shape asymmetry ratio has been
presented here for a general case. It is shown that Fano line-shape becomes
less asymmetric as \q is increased and finally becomes completely symmetric in
the limiting condition of q equal to infinity. Asymmetry ratios of Fano
line-shapes have been calculated and are found to be in good consonance with
the reported expressions for asymmetry ratio as a function of Fano parameter.
Application of this derivation is also mentioned for explanation of asymmetry
to symmetry transition of Fano line-shape in quantum confined silicon
nanostructures.Comment: 3 figures, Latex files, Theoretica
Higher-order ratios of baryon number cumulants
The relevance of higher order cumulants of net baryon number fluctuations for
the analysis of freeze-out and critical conditions in heavy-ion collisions at
LHC and RHIC is addressed. The sign structure of the higher order cumulants in
the vicinity of the chiral crossover temperature might be a sensitive probe and
may allow to elucidate their relation to the QCD phase transition. We calculate
ratios of generalized quark-number susceptibilities to high orders in three
flavor QCD-like models and investigate their sign structure close to the chiral
crossover line.Comment: presented at the International Conference "Critical Point and Onset
of Deconfinement - CPOD 2011", Wuhan, November 7-11, 2011; version to appear
in Cent. Eur. J. Phy
Diversity in the Tail of the Intersecting Brane Landscape
Techniques are developed for exploring the complete space of intersecting
brane models on an orientifold. The classification of all solutions for the
widely-studied T^6/Z_2 x Z_2 orientifold is made possible by computing all
combinations of branes with negative tadpole contributions. This provides the
necessary information to systematically and efficiently identify all models in
this class with specific characteristics. In particular, all ways in which a
desired group G can be realized by a system of intersecting branes can be
enumerated in polynomial time. We identify all distinct brane realizations of
the gauge groups SU(3) x SU(2) and SU(3) x SU(2) x U(1) which can be embedded
in any model which is compatible with the tadpole and SUSY constraints. We
compute the distribution of the number of generations of "quarks" and find that
3 is neither suppressed nor particularly enhanced compared to other odd
generation numbers. The overall distribution of models is found to have a long
tail. Despite disproportionate suppression of models in the tail by K-theory
constraints, the tail in the distribution contains much of the diversity of
low-energy physics structure.Comment: 48 pages, 8 figure
F-Theory and the Mordell-Weil Group of Elliptically-Fibered Calabi-Yau Threefolds
The Mordell-Weil group of an elliptically fibered Calabi-Yau threefold X
contains information about the abelian sector of the six-dimensional theory
obtained by compactifying F-theory on X. After examining features of the
abelian anomaly coefficient matrix and U(1) charge quantization conditions of
general F-theory vacua, we study Calabi-Yau threefolds with Mordell-Weil
rank-one as a first step towards understanding the features of the Mordell-Weil
group of threefolds in more detail. In particular, we generate an interesting
class of F-theory models with U(1) gauge symmetry that have matter with both
charges 1 and 2. The anomaly equations --- which relate the Neron-Tate height
of a section to intersection numbers between the section and fibral rational
curves of the manifold --- serve as an important tool in our analysis.Comment: 29 pages + appendices, 5 figures; v2: minor correction
5-10 GeV Neutrinos from Gamma-Ray Burst Fireballs
A gamma-ray burst fireball is likely to contain an admixture of neutrons, in
addition to protons, in essentially all progenitor scenarios. Inelastic
collisions between differentially streaming protons and neutrons in the
fireball produce muon neutrinos (antineutrinos) of ~ 10 GeV as well as electron
neutrinos (antineutrinos) of ~ 5 GeV, which could produce ~ 7 events/year in
kilometer cube detectors, if the neutron abundance is comparable to that of
protons. Photons of ~ 10 GeV from pi-zero decay and ~ 100 MeV electron
antineutrinos from neutron decay are also produced, but will be difficult to
detect. Photons with energies < 1 MeV from shocks following neutron decay
produce a characteristic signal which may be distinguishable from the
proton-related MeV photons.Comment: 4 pages, latex, 1 figure, aps style files. Final version, accepted in
Phys.Rev.Lett., 6/22/2000; some clarifications in the text, same conclusion
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