14 research outputs found
Off-shell extension of S-matrix elements and tachyonic effective actions
We show that the on-shell S-matrix elements of four open string massless
scalars, two scalars and two tachyons, and four open string tachyons in the
super string theory can be written in a unique form. We then propose an
off-shell extension for the S-matrix element of four scalars which is
consistent, in the low energy limit, with the Dirac-Born-Infeld effective
action. Using a similar off-shell extension for the S-matrix element of two
scalars and two tachyons and for the S-matrix element of four tachyons, we show
that they are fully consistent with the tachyonic DBI action.Comment: Latex, 17 pages, v3:a paragraph comparing off-shell and on- shell
amplitudes added, reference adde
Non-minimally Coupled Tachyonic Inflation in Warped String Background
We show that the non-minimal coupling of tachyon field to the scalar
curvature, as proposed by Piao et al, with the chosen coupling parameter does
not produce the effective potential where the tachyon field can roll down from
T=0 to large along the slope of the potential. We find a correct choice of
the parameters which ensures this requirement and support slow-roll inflation.
However, we find that the cosmological parameter found from the analysis of the
theory are not in the range obtained from observations. We then invoke warped
compactification and varying dilaton field over the compact manifold, as
proposed by Raeymaekers, to show that in such a setup the observed parameter
space can be ensured.Comment: minor typos corrected and references adde
Inflation with improved D3-brane potential and the fine tunings associated with the model
We investigate brane-antibrane inflation in a warped deformed conifold
background that includes contributions to the potential arising from imaginary
anti-self-dual (IASD) fluxes including the term with irrational scaling
dimension discovered recently. We find that the model can give rise to required
number of e-foldings; observational constraint on COBE normalization is easily
satisfied and low value of the tensor to scalar ratio of perturbations is
achieved. We observe that these corrections to the effective potential help in
relaxing the severe fine tunings associated with the earlier analysis.Comment: 8 pages, 4 figures; typos corrected, minor clarifications and new
refs added, to appear in epj
S-matrix elements and off-shell tachyon action with non-abelian gauge symmetry
We propose that there is a unique expansion for the string theory S-matrix
elements of tachyons that corresponds to non-abelian tachyon action. For those
S-matrix elements which, in their expansion, there are the Feynman amplitudes
resulting from the non-abelian kinetic term, we give a prescription on how to
find the expansion. The gauge invariant action is an expanded action,
and the tachyon mass which appears as coefficient of many different
couplings, is arbitrary. We then analyze in details the S-matrix element of
four tachyons and the S-matrix element of two tachyons and two gauge fields, in
both bosonic and superstring theories, in favor of this proposal. In the
superstring theory, the leading terms of the non-abelian gauge invariant
couplings are in agreement with the symmetrised trace of the direct non-abelian
generalization of the tachyonic Born-Infeld action in which the tachyon
potential is consistent with . In the bosonic
theory, on the other hand, the leading terms are those appear in superstring
case as well as some other gauge invariant couplings which spoils the
symmetrised trace prescription. These latter terms are zero in the abelian
case.Comment: Latex, 27 pages, no figures,v4:change the introduction section, add
some notes to clarify the idea, add reference
Synthesis and Characterisation of Pb [II] Complexes of Liquid Crystalline Macrocyclic Ligands
Realâtime hardwareâ and softwareâinâtheâloop simulation of decentralised distribution network control architecture
A DEMOGRAPHIC PARADOX: CAUSES AND CONSEQUENCES OF FEMALE GENITAL CUTTING IN NORTHEASTERN AFRICA
Measurement of electrons from semileptonic heavy-flavour hadron decays at midrapidity in pp and PbâPb collisions at âsNN = 5.02 TeV
The differential invariant yield as a function of transverse momentum (pT) of electrons from semileptonic heavy-flavour hadron decays was measured at midrapidity in central (0â10%), semi-central (30â50%) and peripheral (60â80%) leadâlead (PbâPb) collisions at âsNN = 5.02 TeV in the pT intervals 0.5â26 GeV/c (0â10% and 30â50%) and 0.5â10 GeV/c (60â80%). The production cross section in protonâproton (pp) collisions at âs = 5.02 TeV was measured as well in 0.5 < pT < 10 GeV/c and it lies close to the upper band of perturbative QCD calculation uncertainties up to pT = 5 GeV/c and close to the mean value for larger pT. The modification of the electron yield with respect to what is expected for an incoherent superposition of nucleonânucleon collisions is evaluated by measuring the nuclear modification factor RAA. The measurement of the RAA in different centrality classes allows in-medium energy loss of charm and beauty quarks to be investigated. The RAA shows a suppression with respect to unity at intermediate pT, which increases while moving towards more central collisions. Moreover, the measured RAA is sensitive to the modification of the parton distribution functions (PDF) in nuclei, like nuclear shadowing, which causes a suppression of the heavy-quark production at low pT in heavy-ion collisions at LHC