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R. Akhoury

Publications and source records attributed to R. Akhoury.

At least 19 recordsLinked to original sources
arXiv2009

A Possible Late Time $Λ$CDM-like Background Cosmology in Relativistic MOND Theory

In the framework of Relativistic MOND theory (TeVeS), we show that a late time background $Λ$CDM cosmology can be attained by choosing a specific $F(μ)$ that also meets the requirement for the existence of Newtonian and MOND limits. We investigate the dynamics of the scalar field $ϕ$ under our chosen $F(μ)$ and show that the "slow roll" regime of $ϕ$ corresponds to a dynamical attractor, where the whole system reduces to $Λ$CDM cosmology.

astro-ph↗
arXiv2003

The Large-x Factorization of the Longitudinal Structure Function

A leading-twist factorization formula is derived for the longitudinal structure function in the x -->1 limit of deeply inelastic scattering. This is achieved by defining a new jet function which is gauge independent and probes the transverse momentum of the struck parton in the target. In moment space, terms of order (\ln^k N)/N, which are the leading ones for F_L, are shown to be resummable through the cusp anomalous dimension γ_K and the anomalous dimension γ_{J^\prime} of the new jet function. This anomalous dimension is computed to O(α_s). The suggested factorization for F_L reproduces the fixed order results known to O(α_s^2). The general ideas for resumming the terms of order (\ln^k N)/N in moment space may be extended to the other structure functions and to other inclusive processes near the elastic limit.

hep-ph↗
arXiv2003

Minimal Length Uncertainty Relation and the Hydrogen Spectrum

Modifications of Heisenberg's uncertainty relations have been proposed in the literature which imply a minimum position uncertainty. We study the low energy effects of the new physics responsible for this by examining the consequent change in the quantum mechanical commutation relations involving position and momenta. In particular, the modifications to the spectrum of the hydrogen atom can be naturally interpreted as a varying (with energy) fine structure constant. From the data on the energy levels we attempt to constrain the scale of the new physics and find that it must be close to or larger than the weak scale. Experiments in the near future are expected to change this bound by at least an additional order of magnitude.

hep-ph↗
arXiv2002

On the Resummation of Large QCD Corrections to photon photon to b anti-b

We study the resummation of large QCD radiative corrections up to the next to leading logarithmic accuracy to the process photon photon to b anti-b; i.e., we resum logarithms of the type alpha_s^p log^{2p}{m^2/s} and alpha_s^p log^{2p-1}{m^2/s} (m is the quark mass). The only source of all the logarithms to this accuracy is the off-shell Sudakov form factor included into the triangle topologies of the one-loop box diagram. We prove that any other configurations of diagrams to this accuracy, either cancel in subgroups or develop a universal on-shell Sudakov exponent due to the final quark anti-quark lines. We study the mechanism of cancellations between the different diagrams, which leads to the simple resummed results. We show the cancellation explicitly at three loops for the leading and at two loops for the next-to-leading logarithms. We also point out the general mechanism responsible for it, and discuss how it can be extended to higher orders.

hep-ph↗
arXiv2001

On the Resummation of Large QCD Logarithms in Higgs -> 2 Photons Decay

We study the strong corrections to the Higgs coupling to two photons. This coupling is the dominant mechanism for Higgs production in photon-photon collisions. In addition, the two photon decay mode of the Higgs is an important and relatively background free channel of relevance at the LHC and the Tevatron. We develop a method for the resummation of large QCD corrections in the form of Sudakov-like logarithms of the type α_s^n\ln^{2n}(m/m_H) and α_s^n\ln^{2n-1}(m/m_H) (where m is the light quark mass) which can contribute to this process in certain models (for example, the MSSM for large tan β) up to next-to-leading-logarithmic (NLL) accuracy. The NLL correction is moderate, the substantial part of which comes from terms not related to running coupling effects.

hep-ph↗
arXiv2000

A Variational Principle for Radial Flows in Holographic theories

We develop furthur the correspondence between a d+1 dimensional theory and a d dimensional one with the "radial" (d+1)th corodinate ρplaying the role of an evolution parameter. We discuss the evolution of an effective action defined on a d dimensional surface charactarized by ρby means of a new variational principle. The conditions under which the flow equations are valid are discussed in detail as is the choice of boundary conditions. It is explained how domain walls may be incorporated in the framework and some generalized junction conditions are obtained. The general principles are illustrated on the example of a supergravity theory on AdS_{d+1}.

hep-th↗
arXiv2000

A Note on Large Extra Dimensions

We study corrections to the photon-propagator in a recently proposed model, where gravity lives in 4+n dimensions and Standard Model fields in 4 dimensions. We find a correction to the form factor of the photon that can be constrained by QED tests.

hep-ph↗
arXiv1998

An operator expansion for the elastic limit

A leading twist expansion in terms of bi-local operators is proposed for the structure functions of deeply inelastic scattering near the elastic limit $x \to 1$, which is also applicable to a range of other processes. Operators of increasing dimensions contribute to logarithmically enhanced terms which are supressed by corresponding powers of $1-x$. For the longitudinal structure function, in moment ($N$) space, all the logarithmic contributions of order $\ln^k N/N$ are shown to be resummable in terms of the anomalous dimension of the leading operator in the expansion.

hep-ph↗
arXiv1998

A novel factorization for $F_L$ in the large $x$ limit

A novel factorization formula is presented for the longitudinal structure function $F_L$ near the elastic region $x \to 1$ of deeply inelastic scattering. In moment space this formula can resum all contributions to $F_L$ that are of order $\ln^k N/N$. This is achieved by defining a new jet function which probes the transverse momentum of the struck parton in the target at leading twist. The anomalous dimension $γ_{J^\prime}$ of this new jet operator generates in moment space the logarithmic enhancements coming from the fragmentation of the current jet in the final state. It is also shown how the suggested factorization for $F_L$ is related to the corresponding one for $F_2$ in the same kinematic region.

hep-ph↗
arXiv1998

Cancellation of $1/m_Q$ Corrections to the Inclusive Decay Width of a Heavy Quark

We consider the infrared sensitivity of the inclusive heavy quark decay width in perturbation theory. It is shown by explicit calculations to the second loop order (when the non-abelian nature of the QCD interactions first become apparent) that all infrared sensitive terms to logarithmic and linear accuracy cancel when the decay width is expressed in terms of the short distance mass. This in turn implies the absense of any non perturbative $1/m_Q$ power corrections to the decay width. The cancellation is shown algebraically at the level of the Feynman integrands without any use of an explicit infrared cutoff. This result is in accord with the implications of the KLN theorem.

hep-ph↗
arXiv1997

On Non Perturbative Corrections to the Potential for Heavy Quarks

We discuss non perturbative corrections to the Coulomb-like potential of heavy quarks at short distances. We consider both the standard framework provided by infrared renormalons and the assumption that confinement does not allow weak fields to penetrate the vacuum. In the former case the leading correction at short distances turns out to be quadratic in r for static quarks. In the latter case we find a potential which is proportional to r as r rightarrow 0. We point out that similar effects arise due to a new kind of non perturbative correction proportional to 1/Q^2, which is unaccounted for by the operator product expansion and which was recently discussed within a different framework. Phenomenological implications of the linear correction to the potential are briefly reviewed.

hep-ph↗
arXiv1997

Power Corrections and the Gaussian Form of the Meson Wave Function

The wave function of a light pseudoscalar meson is considered and nonperturbative corrections as signaled by perturbation theory are calculated. Two schemes are used, the massive gluon and the running coupling scheme. Both indicate the presence of leading power corrections of ${\cal O}(b^2)$, whose exponentiation leads to a Gaussian dependence of the wave function on the impact parameter $b$. The dependence of this correction on the light cone energy fractions of the quark and the antiquark is discussed and compared with other models for the meson.

hep-ph↗
arXiv1997

The Physics of the Ultraviolet Renormalon

We review the physics of the ultraviolet renormalon. This mini-review is intended to be a sequel to the review by the same authors at the "QCD '96" conference last year (hep-ph/9610492).

hep-ph↗
arXiv1997

Order $N_fα^2$ Corrections in Low-Energy Electroweak Processes

We provide a compendium of techniques that can be used to compute $O(N_fα^2)$ corrections to low-energy electroweak processes. Specifically, these are the 2-loop electroweak corrections containing a light fermion loop. It is shown that the vast majority of such corrections can be reduced to expressions involving a universal master integral for which an exact analytic form in dimensional regularization is given. The only exceptions are certain photon vacuum polarization diagrams. Examples are presented for diagrams that occur in a variety of processes of practical interest.

hep-ph↗
arXiv1997

Renormalons and 1/Q^2 Corrections

We argue that the appearance of the Landau pole in the running coupling of QCD introduces 1/Q^2 power corrections in current correlation functions. These terms are not accounted for by the standard operator product expansion and is the price to be paid for the lack of a unique definition of the running coupling at the 1/Q^2 level. We review also possible phenomenological implications of the 1/Q^2 terms in an alternative language of the ultraviolet renormalon.

hep-ph↗
arXiv1997

The KLN Theorem and Soft Radiation in Gauge Theories: Abelian Case

We present a covariant formulation of the Kinoshita, Lee, Nauenberg (KLN) theorem for processes involving the radiation of soft particles. The role of the disconnected diagrams is explored and a rearrangement of the perturbation theory is performed such that the purely disconnected diagrams are factored out. The remaining effect of the disconnected diagrams results in a simple modification of the usual Feynman rules for the S-matrix elements. As an application, we show that when combined with the Low theorem, this leads to a proof of the absense of the $1/Q$ corrections to inclusive processes (like the Drell-Yan process). In this paper the abelian case is discussed to all orders in the coupling.

hep-ph↗
arXiv1997

Renormalon Variety in Deep Inelastic Scattering

We discuss the renormalon-based approach to power corrections in non-singlet deep inelastic scattering structure functions and compare it with the general operator product expansion. The renormalon technique and its variations relate the power corrections directly to infrared-sensitive parameters such as the position of the Landau pole Λ_{QCD} or the infinitesimal gluon mass λ. In terms of the standard OPE these techniques unify evaluations of the coefficient functions and of matrix elements. We argue that in case of deep inelastic scattering there is a proliferation of competeing infrared sensitive parameters. In particular we consider the gluon and quark masses, virtuality of quarks and Λ_{QCD} as possible infrared cut offs and compare the emerging results. In the standard renormalon technique where Λ_{QCD} is the infrared parameter, the argument of the running coupling is crucial to obtain the correct x dependance of the structure functions. Finally we discuss the limitations of the use of the renormalon based methods for determining of the x dependance of the power corrections.

hep-ph↗