arXiv subjects
Publications and source records attributed to N. K. Pak.
The magnetization current that appears in the non-relativistic limit of the Dirac equation is derived starting from the Pauli equation.
We study the radiative dileptonic $B \rar γl^+ l^- $ transition in the presence of a universal extra dimension in the Applequist-Cheng-Dobrescu model. In particular, using the corresponding form factors calculated via light cone QCD sum rules, we analyze the branching ratio and double lepton polarization asymmetries related to this channel and compare the results with the predictions of the standard model. We show how the results deviate from predictions of the standard model at lower values of the compactification factor ($1/R $) of extra dimension.
Transformations involving only local operations assisted with classical communication are investigated for multipartite entangled pure states having tensor rank 2. All necessary and sufficient conditions for the possibility of deterministically converting truly multipartite, rank-2 states into each other are given. Furthermore, a chain of local operations that successfully achieves the transformation has been identified for all allowed transformations. The identified chains have two nice features: (1) each party needs to carry out at most one local operation and (2) all of these local operations are also deterministic transformations by themselves. Finally, it is found that there are disjoint classes of states, all of which can be identified by a single real parameter, which remain invariant under deterministic transformations.
The behavior of the geometric phase gained by a single spin-1/2 nucleus immersed into a thermal or a squeezed environment is investigated. Both the time dependence of the phase and its value at infinity are examined against several physical parameters. It is observed that for some intermediate ranges of the temperature and the coupling strength, the presence of squeezing enhances the geometric phase.
The gravitational Higgs mechanism proposed by 't Hooft in arXiv:0708.3184 involves the spacetime metric g_{mu nu} as well as the induced metric \bar{g}_{mu nu} proportional to η_{a b} \partial_{mu} ϕ^a \partial_{nu} ϕ^b where ϕ^{a} (a=0,...,3), as we call it, break all four diffeomorphisms spontaneously via the vacuum expectation values < ϕ^a > proportional to x^a. In this framework, we construct and analyze the most general action density in terms of various invariants involving the curvature tensors, connexion coefficients, and the contractions and the determinants of the two metric fields. We show that this action admits a consistent expansion about the flat background such that the resulting Lagrangian possesses several novel features not found in the linearized Einstein-Hilbert Lagrangian with Fierz-Pauli mass term (LELHL-FP): (i) its kinetic part generalizes that of LELHL-FP by weighing the corresponding structures with certain coefficients generated by invariants, (ii) the entire Lagrangian is ghost-- and tachyon--free for mass terms not necessarily in the Fierz-Pauli form, and, (iii) a consistent mass term is generated with no apparent need to higher derivative couplings.
We study the effects of unparticle physics in the pair productions of top quarks at the LHC and ILC. By considering vector, tensor and scalar unparticle operators, as appropriate, we compute the total cross sections for pair production processes depending on scale dimension $d_{\U}$. We find that the existence of unparticles would lead to measurable enhancements on the SM predictions at the LHC. In the case of ILC this may become two orders of magnitude larger than that of SM, for smaller values of $d_\U$, a very striking signal for unparticles.
We study the single production of top quarks in $e^+e^-, ep$ and $pp$ collisions in the context of unparticle physics through the Flavor Violating (FV) unparticle vertices and compute the total cross sections for single top production as functions of scale dimension $d_{\U}$. We find that among all, LHC is the most promising facility to probe the unparticle physics via single top quark production processes.
A partial wave analysis using the basis of the total angular momentum operator J_3 is carried out for the first order Born amplitude of a Dirac particle in an Aharonov-Bohm (AB)potential. It is demonstrated that the s-partial wave contributes to the scattering amplitude in contrast to the case with scalar non-relativistic particles.We suggest that this explains the fact that the first order Born amplitude of a Dirac particle coincides with the exact amplitude expanded to the same order, where it does not for a scalar particle. An interesting algebra involving the Dirac velocity operator and the angular observables is discovered and its consequences are exploited.
Taking the most general two-doublet models with explicit CP violation in the Higgs sector but no phase in the CKM matrix, we determine the correlation between the Higgs and Kaon sectors using the experimental values of $ΔM_K$ and $ε_K$. It is found that: there is a direct correlation between strength of FCNC couplings and the Higgs masses, and the lightest Higgs is nearly pure CP-even, but this small CP-odd composition gives large enough contribution to $ε_K$.
The relativistic scattering of a spin-1/2 particle from an infinitely long solenoid is considered in the framework of covariant perturbation theory. The first order term agrees with the corresponding term in the series expansion of the exact amplitude, and second order term vanishes, thus proving that Born approximation is consistent.
Q-balls generically exist in the supersymmetric extensions of the standard model. Taking into account the additional sources of CP violation, which are naturally accomodated by the supersymmetric models, it is shown that the Q-ball matter depends additively on individual CP phases, whereas mass per unit charge in the Q-ball depends only on the relative phases. There are regions of the parameter space where there is no stable Q-ball solution in the CP-conserving limit whereas finite CP phases induce a stable Q-ball.
Using the experimental result on b\to sγand theoretical result on b\to sg, a four -generation SM is analysed to constrain the rephasing-invariant combinations of the CKM matrix and masses of the fourth generation quarks.
We discuss the $e^{+}e^{-}\to (h A)\to bbbb$ cross section in an Abelian extended SM. We work in that minimum of the scalar potential for which Higgs trilier coupling is greater than the soft mass parameters. We find that nex-to-lightest Higgs gives the essential contribution to the cross section in the small $Z-Z'$ mixing angle and leptophobic $Z'$ limit.
We analyze the Higgs production via the Higgs-strahlung process $e^{+}e^{-}\to h_{k}{\it{l}}^{+}{\it{l}}^{-}$ in an Abelian Extended Supersymmetric SM. We work in the large Higgs trilinear coupling driven minimum of the potential, and find that the next-to-lightest Higgs cannot be produced by this process. Other Higgs scalars, namely the lightest and the heaviest, have cross sections comparable to that in the pure SM. It is found that the present model has observable differences with the other popular model, NMSSM, in the same type of minimum.
For an Abelian extended Supergravity model, we investigate some important low energy parameters: \tanβ, Z-Z' mixing angle, lightest CP-even Higgs mass bound, Z' mass, and effective μparameter. By integrating the RGE's from string scale down to the weak scale we constuct the scalar potential, and analyze the quantities above at the tree- and one-loop levels by including the contributions of top squarks and top quark in the effective potential. PACS: 04.65.+e, 12.60.Jv
The radiative B -> tau^+ tau^- gamma decay is investigated in the framework of the Standard Model. When only short (short and long together) distance contributions are taken into account, the Branching Ratio is found as 9.54x10^(-9) (1.52x10^(-8)), for the value of the cut delta = 0.01 imposed on the photon energy.
We calculate the strong coupling constants g_(P^(**)P^(*)π), where P^(**)(D^(**), B^(**)) is the 1^+ p-wave state, in the framework of the light cone QCD sum rules, and using these values of g_(P^(**)P^(*) pi, we compute the hadronic decay widths for D^(**) -> D^* pi and B^(**) -> B^* pi.
The cvariant path integral quantization of the theory of the scalar and spinor particles interacting through the abelian and non-Abelian Chern-Simons gauge fields is carried out and is shown to be mathematically ill defined due to the absence of the transverse components of these gauge fields. This is remedied by the introduction of the Maxwell or the Maxwell-type (in the non-Abelian case)term which makes the theory superrenormalizable and guarantees its gauge-invariant regularization and renormalization. The generating functionals are constructed and shown to be formally the same as those of QED (or QCD) in 2+1 dimensions with the substitution of the Chern-Simons propagator for the photon (gluon) propagator. By constructing the propagator in the general case, the existence of two limits; pure Chern-Simons and QED (QCD) after renormalization is demonstrated. By carrying out carefully the path integral quantization of the non-Abelian Chern-Simons theories using the De Witt-Fadeev-Popov and the Batalin-Fradkin- Vilkovisky methods it is demonstrated that there is no need to quantize the dimensionless charge of the theory. The main reason is that the action in the exponent of the path integral is BRST-invariant which acquires a zero winding number and guarantees the BRST renormalizability of the model. The S-matrix operator is constructed, and starting from this S-matrix operator novel topological unitarity identities are derived that demand the vanishing of the gauge-invariant sum of the imaginary parts of the Feynman diagrams with a given number of intermediate on-shell topological photon lines in each order of perturbation theory. These identities are illustrated by an explicit example.