Searcharxiv⌕ Search

arXiv subjects

Igor Halperin

Publications and source records attributed to Igor Halperin.

52 records · Page 3Linked to original sources

Bayesian Entropic Inverse Theory Approach to Implied Option Pricing with Noisy Data

A popular approach to nonparametric option pricing is the Minimum Cross Entropy (MCE) method based on minimization of the relative Kullback-Leibler entropy of the price density distribution and a given reference density, with observable option prices serving as constraints. When market prices are noisy, the MCE method tends to overfit the data and often becomes unstable. We propose a non-parametric option pricing method whose input are noisy market prices of arbitrary number of European options with arbitrary maturities. Implied transition densities are calculated using the Bayesian inverse theory with entropic priors, with a reference density which may be estimated by the algorithm itself. In the limit of zero noise, our approach is shown to reduce to the canonical MCE method generalized to a multi-period case. The method can be used for a non-parametric pricing of American/Bermudan options with a possible weak path dependence.

cond-mat.stat-mech↗

"Integrating in" and Effective Lagrangian for Non-Supersymmetric Yang-Mills Theory

Recently a non-supersymmetric analog of Veneziano-Yankielowicz (VY) effective Lagrangian has been proposed and applied for the analysis of the theta dependence in pure Yang-Mills theory. This effective Lagrangian is similar in many respects to the VY construction and, in particular, exhibits a kind of low energy holomorphy which is absent in the full YM theory. Here we incorporate a heavy fermion into this effective theory by using the "integrating in" technique. We find that, in terms of this extended theory, holomorphy of the effective Lagrangian for pure YM theory naturally implies a holomorphic dependence on the heavy fermion mass. It is shown that this analysis fixes, under certain assumptions, a dimensionless parameter which enters the effective Lagrangian and determines the number of nondegenerate vacuum sectors in pure YM theory. We also compare our results for the vacuum structure and theta dependence to those obtained recently by Witten on the basis of AdS/CFT correspondence.

hep-th↗

Axion potential, topological defects and CP-odd bubbles in QCD

It follows on general grounds that the theta dependence in QCD is more complicated than suggested by the large N_c approach or instanton arguments. Generically, the vacuum energy E_{vac}(θ) is a multi-valued function of θadmitting the existence of metastable states. We discuss decays of such metastable vacua in the theory with and without the axion, and point out the potential relevance of this and related phenomena for constraining a dark matter axion. Based on the analysis of the axion potential, an idea for a new axion search experiment at RHIC is suggested. It is noted that the false vacuum decay proceeds with maximal violation of CP, even if θ= 0. We further speculate that the famous Sakharov criteria for baryogenesis could be satisfied at the QCD scale.

hep-ph↗

On Topological Susceptibility, Vacuum Energy and Theta Dependence in Gluodynamics

We suggest that the topological susceptibility in gluodynamics can be found in terms of the gluon condensate using renormalizability and heavy fermion representation of the anomaly. Analogous relations can be also obtained for other zero momentum correlation functions involving the topological density operator. Using these relations, we find the theta dependence of the condensates , and of the partition function for small theta and an arbitrary number of colors.

hep-ph↗

Anomalous Effective Lagrangian and Theta Dependence in QCD at Finite N_c

We generalize the large N_c Di Vecchia-Veneziano-Witten (VVW) effective chiral Lagrangian to the case of finite N_c by constructing the anomalous effective Lagrangian for QCD. The latter is similar to its SUSY counterpart, and has a holomorphic structure. The VVW construction is then recovered, along with 1/N_c corrections, after integrating out the heavy "glueball" fields. A new mass formula for eta' meson in terms of QCD condensates is obtained. The picture of theta dependence in QCD for finite N_c is more complicated than the one predicted by the large N_c approach.

hep-ph↗

Can Theta/N Dependence for Gluodynamics be Compatible with 2 pi Periodicity in Theta ?

In a number of field theoretical models the vacuum angle θenters physics in the combination θ/N, where N stands generically for the number of colors or flavors, in an apparent contradiction with the expected 2 πperiodicity in θ. We argue that a resolution of this puzzle is related to the existence of a number of different θdependent sectors in a finite volume formulation, which can not be seen in the naive thermodynamic limit V -> \infty. It is shown that, when the limit V -> \infty is properly defined, physics is always 2 πperiodic in θfor any integer, and even rational, values of N, with vacuum doubling at certain values of θ. We demonstrate this phenomenon in both the multi-flavor Schwinger model with the bosonization technique, and four-dimensional gluodynamics with the effective Lagrangian method. The proposed mechanism works for an arbitrary gauge group.

hep-ph↗

Why is the B -> eta' X decay width so large ?

New mechanism for the observed inclusive B -> η'X decay is suggested. We argue that the dominant contribution to this amplitude is due to the Cabbibo favored b -> \bar{c}cs process followed by the transition \bar{c}c -> η'. A large magnitude of the "intrinsic charm" component of η' is of critical importance in our approach. Our results are consistent with an unexpectedly large Br(B -> η'+X) \sim 10^{-3} recently announced by CLEO. We stress the uniqueness of this channel for 0^{-+} gluonia search.

hep-ph↗

B -> K eta' decay as unique probe of eta' meson

A theory of the B -> K η' decay is proposed. It is based on the Cabbibo favored b -> \bar{c} c s process followed by a direct materialization of the \bar{c} c pair into the η'. This mechanism works due to a non-valence Zweig rule violating c-quark component of the η', which is unique to its very special nature. This non-perturbative "intrinsic charm" content of the η' is evaluated using the Operator Product Expansion and QCD low energy theorems. Our results are consistent with an unexpectedly large Br(B -> K η') \simeq 7.8 \cdot 10^{-5} recently announced by CLEO.

hep-ph↗

Polarized Intrinsic Charm as a Possible Solution to the Proton Spin Problem

We argue that a large fraction of the proton spin comes from a contribution due to a nonperturbative intrinsic charm component of the proton. An account of this contribution removes an apparent contradiction between the data and exact Kühn-Zakharov low energy theorem. On the other hand, we show that a large intrinsic charm spin component of the proton is implied by recent CLEO data on B -> η' decays. We argue that the proton spin and B -> η' data are manifestations of the same physics with full agreement between two different estimates of the intrinsic charm component of the proton spin. Our results suggest an explanation of the polarized DIS data and have profound consequences for future experiments on charm production off a polarized proton. A microscopic origin of the effect is related to strong well-localized gluon fluctuations (instantons) where the mass of the charmed quark is not a suppression factor at all, as was naively expected earlier.

hep-ph↗

Conformal symmetry on the light cone and nonleading twist distribution amplitudes of massive vector meson

A complete set of asymptotic three particle light cone distribution amplitudes of twist 3 and 4 for a transversely polarized massive vector meson built out of massless current quarks is constructed. The method used is based on a modified conformal projectors technique which allows to handle kinematical corrections due to a finite hadron mass. Consequences of our finding for the ρ-meson hard diffractive electroproduction and γρπform factor are discussed. Our results may imply a breakdown of OPE for some exclusive processes beyond the leading twist level.

hep-ph↗

Hard diffractive electroproduction, transverse momentum distribution and QCD vacuum structure

We study the impact of the "intrinsic" hadron transverse momentum on the pre-asymptotic behavior of the diffractive electroproduction of longitudinally polarized $ ρ$-meson. Surprisingly, we find the onset of the asymptotic regime in this problem to be rather low, Q^2 ~ 10 GeV^2 where power corrections due to the transverse momentum do not exceed 20 % in the amplitude. This drastically contrasts with exclusive amplitudes where the asymptotics starts at much higher Q^2 = 50 - 100 GeV^2. The sources of such unexpected behavior are traced back to some general (the quark-hadron duality) as well as more silent (properties of higher dimensional vacuum condensates) features of QCD.

hep-ph↗

Regge asymptotics and color suppressed heavy meson decays

We discuss a possible generation of color suppressed B-decays amplitudes through a soft final state interaction. As a typical example, we consider in detail the decay $ \bar{B}^{0} \rightarrow D^{0} π^{0} $ (and also $ \bar{B}^{0} \rightarrow 2 π^{0} $). We show that in the approximation of the two particle unitarity and at zero order in $ α_{s} $ this process can be related to the weak decay $ \bar{B}^{0} \rightarrow D^{+} π^{-} $ followed by the strong charge exchange scattering in the Regge kinematics. We estimate the amplitude of this process using the light cone QCD sum rule technique and find that it is supppressed as a power of $ 1/m_{B} $ in comparison to the amplitude generated by the effective non-leptonic Hamiltonian, but remains important for the physical value of $m_{B}$.

hep-ph↗

Quantum KAM Technique and Yang-Mills Quantum Mechanics

We study a quantum analogue of the iterative perturbation theory by Kolmogorov used in the proof of the Kolmogorov-Arnold-Moser (KAM) theorem. The method is based on sequent canonical transformations with a "running" coupling constant $ \lm,\lm^{2},\lm^{4} $ etc. The proposed scheme, as its classical predecessor, is "superconvergent" in the sense that after the n-th step, a theory is solved to the accuracy of order $ \lm^{2^{n-1}} $. It is shown that the Kolmogorov technique corresponds to an infinite resummation of the usual perturbative series. The corresponding expansion is convergent for the quantum anharmonic oscillator due to the fact that it turns out to be identical to the Pade series. The method is easily generalizable to many-dimensional cases. The Kolmogorov technique is further applied to a non-perturbative treatment of Yang-Mills quantum mechanics. A controllable expansion for the wave function near the origin is constructed. For large fields, we build an asymptotic adiabatic expansion in inverse powers of the field. This asymptotic solution contains arbitrary constants which are not fixed by the boundary conditions at infinity. To find them, we approximately match the two expansions in an intermediate region. We also discuss some analogies between this problem and the method of QCD sum rules.

hep-ph↗

Soft Gluon Suppression of $ 1/N_{c} $ Contributions in Color Suppressed Heavy Meson Decays

We discuss the non-factorizable terms in color suppressed (Class II) decays. Our emphasis is on the non-perturbative soft gluon exchange mechanism, which has been previously found to be responsible for the rule of discarding $ 1/N_{c} $ in the Class I decays. The non-factorizable contribution to the decays $ \bar{B}^{0} \rightarrow D^{0} π^{0} $ at the tree level is estimated within the light cone QCD sum rule method which combines the technique of the QCD sum rules with the description of the pion in terms of the set of wave functions of increasing twist. We find that the same soft gluon exchange mechanism tends to cancel the $ 1/N_{c} $ term in the factorized amplitude.

hep-ph↗

Veneziano Ghost Versus Isospin Breaking

It is argued that an account for the Veneziano ghost pole, appearing in resolving the U(1) problem, is necessary for understanding an isospin violation in the $ π- η- η' $ system. By virtue of a perturbative expansion around the $ SU(2)_{V} $ ( $ m_{u} = m_{d} $ ) symmetric Veneziano solution, we find that the ghost considerably suppresses isospin breaking gluon and s-quark matrix elements. We speculate further on a few cases where the proposed mechanism can play an essential role. We discuss the isospin violation in meson-nucleon couplings and its relevance to the problem of charge asymmetric nuclear forces and possible breaking of the Bjorken sum rule. It is shown that the ghost pole could yield the isospin violation of order 2 \% for the $ πN $ couplings and 20 \% for the Bjorken sum rule.

hep-ph↗