0000000001173548
AUTHOR
J. Papavassiliou
Gauge-invariant top-quark form-factors from e(+)e(-) experiments
Motivated by the possibility of experimental determination of top quark form factors in upcoming e+ e- experiments, as recently discussed by Atwood and Soni, we show at the one loop level that the conventionally defined magnetic dipole moment (MDM) form factor of the top quark is gauge dependent, in the class of renormalizable ($R_{\xi}$) gauges. We explicitly calculate its gauge dependence, which, due to the massiveness of the top quark, turns out to be numerically very sizable. We show how to use the S-matrix pinch technique in order to define gauge independent form factors. The real and imaginary parts of the gauge independent MDM form factor are calculated and their dependence on the to…
The QCD Effective Charge to All Orders
Using the pinch technique, we show how to construct the QCD effective charge to all orders.
Magnetic Monopole Search with the Full MoEDAL Trapping Detector in 13 TeV pp Collisions Interpreted in Photon-Fusion and Drell-Yan Production
MoEDAL is designed to identify new physics in the form of stable or pseudostable highly ionizing particles produced in high-energy Large Hadron Collider (LHC) collisions. Here we update our previous search for magnetic monopoles in Run 2 using the full trapping detector with almost four times more material and almost twice more integrated luminosity. For the first time at the LHC, the data were interpreted in terms of photon-fusion monopole direct production in addition to the Drell-Yan-like mechanism. The MoEDAL trapping detector, consisting of 794 kg of aluminum samples installed in the forward and lateral regions, was exposed to 4.0 fb$^{-1}$ of 13 TeV proton-proton collisions at the LHC…
Electroweak Effective Charges and their relation to Physical Cross Sections
In quantum electrodynamics with fermions f = e,\mu..., knowledge of the vacuum polarization spectral function determined from the tree level e^+e^- -> f^+f^- cross sections, together with a single low energy measurement of the fine structure constant \alpha, enables the construction of the one-loop effective charge \alpha_eff(q^2) for all q^2. It is shown how an identical procedure can be followed in the electroweak sector of the Standard Model to construct three gauge-, scale- and scheme-independent one-loop electroweak effective charges and an effective weak mixing angle from the tree level e^+e^- -> W^+W^-, ZH and e^+\nu_e -> W^+Z, W^+\gamma, W^+H differential cross sections, together wi…
Dynamical zero in ν¯e–e− scattering and the neutrino magnetic moment
AbstractThe Standard Model differential cross section for ν¯e–e− elastic scattering vanishes exactly, at lowest order, for forward electrons and incident ν¯e energy close to the rest energy of the electron. This dynamical zero is not induced by a fundamental symmetry of the Lagrangian but by a destructive interference between the left- and right-handed chiral couplings of the electron in the charged and neutral current amplitudes. We show that lowest-order analyses based on this favorable kinematic configuration are only mildly affected by the inclusion of the O(α) radiative corrections in the ν¯e–e− differential cross section, thus providing an excellent opportunity for the search of “new …
BRST-driven cancellations and gauge invariant Green's functions
We study a fundamental, all order cancellation operating between graphs of distinct kinematic nature, which allows for the construction of gauge-independent effective self-energies, vertices, and boxes at arbitrary order.
Extra dimensions at the one loop level: Z -> b(b)over-bar and B-(B)over-bar mixing
We study, at the one loop level, the dominant new physics contributions from extra dimensions to Z -> b(b)over-bar, as well as B-(B)over-bar and K-(K)over-bar mixing. We use a model with one extra dimension containing fermions which live in four dimensions, and gauge bosons and one scalar doublet propagating in five dimensions. We find that the effect of the infinite tower of Kaluza-Klein modes in Z -> b(b)over-bar is finite and gives a negative correction to Rb = Γb/Γh, which is used to set a lower bound of 1 TeV on the compactification scale Mc. On the other hand, we show that the box diagrams contributing to B-(B)over-bar and K-(K)over-bar mixing are divergent and, after proper regulariz…
CPT violation in entangled B0–B¯0 states and the demise of flavour tagging
AbstractWe discuss the demise of flavour tagging due to the loss of the particle–antiparticle identity of neutral B-mesons in the Einstein–Podolsky–Rosen correlated states. Such a situation occurs in cases where the CPT operator is ill-defined, as happens, for example, in quantum gravity models with induced decoherence in the matter sector. The time evolution of the perturbed B0–B¯0 initial state, as produced in B-factories, is sufficient to generate new two-body states. For flavour specific decays at equal times, we discuss two definite tests of the two body entanglement: (i) search for the would-be forbidden B0B0 and B¯0B¯0 states; (ii) deviations from the indistinguishable probability be…