73 research outputs found
Magnetized Domain Walls in the Deconfined Sakai-Sugimoto Model at Finite Baryon Density
The magnetized pure pion gradient () phase in the deconfined
Sakai-Sugimoto model is explored at zero and finite temperature. We found that
the temperature has very small effects on the phase. The thermodynamical
properties of the phase shows that the excitations behave like a scalar
solitonic free particles. By comparing the free energy of the pion gradient
phase to the competing multiquark-pion gradient (MQ-) phase,
it becomes apparent that the pure pion gradient is less thermodynamically
preferred than the MQ- phase. However, in the parameter space
where the baryonic chemical potential is smaller than the onset value of the
multiquark, the dominating magnetized nuclear matter is the pion gradient
phase.Comment: 20 pages, 9 figure
Similarity between Kaluza-Klein and Open-string amplitudes in Diphoton Production
We calculate the tree-level open-string amplitudes for the scattering of four
massless particles with diphoton final states. These amplitudes are required to
reproduce those of standard model at the tree level in the low energy limit.
After low energy stringy corrections, we found that they have similar form to
the same processes induced by exchange of the Kaluza-Klein(KK) excitations of
graviton in ADD scenario. Using this similarity, we apply constraints on the KK
mass scale to the string scale . The results are consistent with
constraints from the 4-fermion scattering, about TeV.Comment: 10 pages, modified reference
Physics beyond the Standard Model and Collider Phenomenology
We briefly review the Standard Model of the particle physics focussing on the gauge hierachy problem and the naturalness problem regarding the stabilization of the light Higgs mass. We list the alternative models which address the hierachy problem in addition to conventional Supersymmetric models and Composite models. They include extra dimensional models and Little Higgs models. We investigate the production of heavy at the linear collider at high centre-of-mass energies at 3 and 5 TeV using the Littlest Higgs model where the global group is . In certain region of the parameter space, the heavy boson induced signals could be distinguishable from the Standard Model background. Based on tree-level open-string scattering amplitudes in the low string-scale scenario, we derive the massless fermion scattering amplitudes. The amplitudes are required to reproduce those of the Standard Model at tree level in the low energy limit. We then obtain four-fermion contact interactions by expanding in inverse powers of the string scale and explore the constraints on the string scale from low energy data. The Chan-Paton factors and the string scale are treated as free parameters. We find that data from the neutral and charged current processes at HERA, Drell-Yan process at the Tevatron, and from LEP-II put lower bounds on the string scale , for typical values of the Chan-Paton factors, in the range TeV, comparable to Tevatron bounds on and masses. We consider the low-energy stringy corrections to the 4-fermion scattering at the linear collider at the 500-GeV centre-of-mass energy. The signals look similar to the contributions from the Kaluza-Klein (KK) graviton exchange but could be distinguishable if there is sufficient number of events. Theoretically, the stringy signals contain both spin 1 and 2 corrections while the KK contains only spin 2. We calculate the tree-level open-string amplitudes for the scattering of four massless particles with diphoton final states. These amplitudes are required to reproduce those of standard model at the tree level in the low energy limit. After low energy stringy corrections, we found that they have similar form to the same processes induced by exchange of the Kaluza-Klein (KK) excitations of graviton in ADD scenario. Using this similarity, we apply constraints on the KK mass scale to the string scale . The results are consistent with constraints from the 4-fermion scattering, about TeV. We construct tree-level four-particle open-string amplitudes relevant to dilepton and diphoton production at hadron colliders. We expand the amplitudes into string resonance (SR) contributions and compare the total cross-section through the first SR with the search at the Tevatron. We establish a current lower bound based on the CDF Run I results on the string scale to be about TeV, and it can be improved to about TeV with 2 fb. At the LHC, we investigate the properties of signals induced by string resonances in dilepton and diphoton processes. We demonstrate the unique aspects of SR-induced signals distinguishable from other new physics, such as the angular distributions and forward-backward asymmetry. A C.L. lower bound can be reached at the LHC for TeV with an integrated luminosity of fb. We emphasize the generic features and profound implications of the amplitude construction. We discuss the stringy gauge ``singlet'' interaction induced by stringy dynamics for scattering of particles. Existence of this stringy interaction could lead to stringent bound on the string scale in the braneworld scenario when it is subject to experimental constraints on proton decay. We discuss IR limit of four-fermion scattering amplitudes in braneworld models including intersecting-branes and SUSY GUT version of it. With certain compactification where instanton effect is negligible, grand unification condition in D6-D6 intersecting-branes scenario subject to experimental constraint on proton decay provides possibility for upper limit on the string scale, , through relationship between the string coupling, , and the string scale. We discuss how IR divergence is related to number of twisted fields we have to introduce into intersection region and how it can change IR behaviour of tree-level amplitudes in various intersecting-branes models. Using number of twisted fields, we identify some intersecting-branes models whose tree-level amplitudes are purely stringy in nature and automatically proportional to at low energy. They are consequently suppressed by the string scale. For comparison, we also derive limit on the lower bound of the string scale from experimental constraint on proton decay induced from purely stringy contribution in the coincident-branes model, the limit is about TeV
Effects of Chameleon Scalar Field on Rotation Curves of the Galaxies
We investigate the effects of chameleon scalar field to the effective density
and pressure of a dark matter halo. The pressure is generated from the
chameleonic fifth force on the matter. We demonstrate that the thick-shell
non-singular boundary condition which forbids singular point leads to extremely
stringent constraint on the matter-chameleon coupling when applied to galaxy.
We argue that chameleon profile with central singularity is more likely to
develop in general physical situation. The chameleonic fifth force from the
chameleon profile with central singularity experienced by the dark matter could
significantly modify the rotation curve of galaxies. The chameleonic fifth
force could generate steeper cusp to the rotation curves in any dark matter
profiles starting from the Navarro-Frenk-White (NFW) to the pseudo-isothermal
(ISO) profile. Upper limits on the coupling constant between the chameleon and
the dark matter are estimated from observational data of the late-type
Low-Surface-Brightness galaxies (LSB). It is in the order of .Comment: 26 pages, 13 figures, 1 table, extended version to include more
viable self-potential and analytic solutions. To be published in IJMP
Dark energy and moduli stabilization of extra dimensions in M^{1+3}xT^2 spacetime
Recently, it was found by Greene and Levin that the Casimir energy of certain
combinations of massless and massive fields in space with extra dimensions play
a crucial role in the accelerated expansion of the late-time universe and
therefore it could serve as a candidate for the dark energy. It also provides a
mechanism in stabilizing the volume moduli of extra dimensions. However, the
shape moduli of the extra dimensions were never taken into account in the
previous work. We therefore study the stabilization mechanism for both volume
and shape moduli due to the Casimir energy in . The result of our study shows that the previously known local
minimum is a saddle point. It is unstable to the perturbations in the direction
of the shape moduli. The new stable local minima stabilizes all the moduli and
drives the accelerating expansion of the universe. The cosmological dynamics
both in the bulk and the radion pictures are derived and simulated. The
equations of state for the Casimir energy in a general torus are derived. Shear
viscosity in extra dimensions induced by the Casimir density in the late times
is identified and calculated, it is found to be proportional to the Hubble
constant.Comment: 19 pages, 7 figures, references adde
Remarks on Limits on String Scale from Proton Decay and Low-Energy amplitudes in Braneworld Scenario
We discuss IR limit of four-fermion scattering amplitudes in braneworld
models including intersecting-branes and SUSY SU(5) GUT version of it. With
certain compactification where instanton effect is negligible, grand
unification condition in D6-D6 intersecting-branes scenario subject to
experimental constraint on proton decay provides possibility for upper limit on
the string scale, , through relationship between the string coupling,
, and the string scale. We discuss how IR divergence is related to number
of twisted fields we have to introduce into intersection region and how it can
change IR behaviour of tree-level amplitudes in various intersecting-branes
models. Using number of twisted fields, we identify some intersecting-branes
models whose tree-level amplitudes are purely stringy in nature and
automatically proportional to at low energy. They are
consequently suppressed by the string scale. For comparison, we also derive
limit on the lower bound of the string scale from experimental constraint on
proton decay induced from purely stringy contribution in the coincident-branes
model, the limit is about TeV.Comment: 14 page
Shear viscosity in holography and effective theory of transport without translational symmetry
Theoretical Physic
Aspects of the Screening Length and Drag Force in Two Alternative Gravity Duals of the Quark-gluon Plasma
We compute the screening length of mesons with different angular momentum
from two gravity dual theories. Both the asymptotically and
Sakai-Sugimoto metrics are considered in the calculations. Using the dual
description of the quark as a classical string ending on the probe brane, we
obtain the interacting potential between the heavy quark and antiquark after
rotating the background metric. The result shows that the screening length of
mesons with different is well fit to . The constant is
determined for by taking advantage of numerical techniques. Finally,
we calculate the drag force and relaxation times from the Sakai-Sugimoto metric
and compare with the ones obtained in the . The application of our
result to charmonium and bottomonium at RHIC and LHC is briefly discussed.Comment: 18 pages, 6 figures, 2 tables, version to appear in JHEP,
acknowledgment adde
Heavy Quarkonium States with the Holographic Potential
The quarkonium states in a quark-gluon plasma is examined with the heavy
quark potential implied by the holographic principle. Both the vanila
AdS-Schwarzschild metric and the one with an infrared cutoff are considered.
The dissociation temperature is calculated by solving the Schr\"o dinger
equation of the potential model. In the case of the AdS-Schwarzschild metric
with a IR cutoff, the dissociation temperatures for and
with the U-ansatz of the potential are found to agree with the lattice results
within a factor of two.Comment: 9 pages with 2 figues in Revte
Does space-time torsion determine the minimum mass of gravitating particles?
We derive upper and lower limits for the massâradius ratio of spin-fluid spheres in EinsteinâCartan theory, with matter satisfying a linear barotropic equation of state, and in the presence of a cosmological constant. Adopting a spherically symmetric interior geometry, we obtain the generalized continuity and TolmanâOppenheimerâVolkoff equations for a Weyssenhoff spin fluid in hydrostatic equilibrium, expressed in terms of the effective mass, density and pressure, all of which contain additional contributions from the spin. The generalized Buchdahl inequality, which remains valid at any point in the interior, is obtained, and general theoretical limits for the maximum and minimum massâradius ratios are derived. As an application of our results we obtain gravitational red shift bounds for compact spin-fluid objects, which may (in principle) be used for observational tests of EinsteinâCartan theory in an astrophysical context. We also briefly consider applications of the torsion-induced minimum mass to the spin-generalized strong gravity model for baryons/mesons, and show that the existence of quantum spin imposes a lower bound for spinning particles, which almost exactly reproduces the electron mass
- âŠ