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Ahmed Rashed

Publications and source records attributed to Ahmed Rashed.

33 records · Page 2Linked to original sources

Multi-Label Network Classification via Weighted Personalized Factorizations

Multi-label network classification is a well-known task that is being used in a wide variety of web-based and non-web-based domains. It can be formalized as a multi-relational learning task for predicting nodes labels based on their relations within the network. In sparse networks, this prediction task can be very challenging when only implicit feedback information is available such as in predicting user interests in social networks. Current approaches rely on learning per-node latent representations by utilizing the network structure, however, implicit feedback relations are naturally sparse and contain only positive observed feedbacks which mean that these approaches will treat all observed relations as equally important. This is not necessarily the case in real-world scenarios as implicit relations might have semantic weights which reflect the strength of those relations. If those weights can be approximated, the models can be trained to differentiate between strong and weak relations. In this paper, we propose a weighted personalized two-stage multi-relational matrix factorization model with Bayesian personalized ranking loss for network classification that utilizes basic transitive node similarity function for weighting implicit feedback relations. Experiments show that the proposed model significantly outperforms the state-of-art models on three different real-world web-based datasets and a biology-based dataset.

cs.LG↗

New physics in inclusive $B \to X_c\ell \barν$ decay in light of $R(D^{(*)})$ measurements

In this work we study the effects of new-physics (NP) operators with different Lorentz structures on the inclusive $B \to X_cτ\barν$ decay and make predictions for the ratio of total decay rates $R(X_c)=\frac{Γ(B \to X_cτ\barν_τ)}{Γ(B \to X_c \ell \barν_\ell)}$ with $\ell=e, μ$, the differential decay rates, $\frac{dΓ}{dq^2}$ and $\frac{dΓ}{dE_τ}$, forward-backward asymmetry $A_{FB}$ and the ratio of the differential decay rates $B(q^2)=\frac{dΓ(B \to X_cτ\barν_τ)/dq^2}{dΓ(B \to X_c \ell \barν_\ell)/dq^2}$. In addition, we introduce some leptoquark models as explicit models of the NP operators and study their effects on the inclusive decay. We consider $\mathcal{O}(α_s)$ radiative and $1/m_b$ nonperturbative corrections to the Standard Model (SM) decay rate and ignore their small effects in the NP contributions.

hep-ph↗

The $B \to πK$ Puzzle Revisited

For a number of years, there has been a certain inconsistency among the measurements of the branching ratios and CP asymmetries of the four $B \to πK$ decays ($B^+ \to π^+ K^0$, $B^+ \to π^0 K^+$, $B^0 \to π^- K^+$, $B^0 \to π^0 K^0$). In this paper, we re-examine this $B \to πK$ puzzle. We find that the key unknown parameter is $|C'/T'|$, the ratio of color-suppressed and color-allowed tree amplitudes. If this ratio is large, $|C'/T'| = 0.5$, the SM can explain the data. But if it is small, $|C'/T'| = 0.2$, the SM cannot explain the $B \to πK$ puzzle -- new physics (NP) is needed. The two types of NP that can contribute to $B \to πK$ at tree level are $Z'$ bosons and diquarks. $Z'$ models can explain the puzzle if the $Z'$ couples to right-handed $u{\bar u}$ and/or $d{\bar d}$, with $g_R^{dd} \ne g_R^{uu}$. Interestingly, half of the many $Z'$ models proposed to explain the present anomalies in $b \to s μ^+ μ^-$ decays have the required $Z'$ couplings to $u{\bar u}$ and/or $d{\bar d}$. Such models could potentially explain both the $b \to s μ^+ μ^-$ anomalies and the $B \to πK$ puzzle. The addition of a color sextet diquark that couples to $ud$ can also explain the puzzle.

hep-ph↗

Phenomenology of $Λ_b \to Λ_c τ\barν_τ$ using lattice QCD calculations

In a recent paper we studied the effect of new-physics operators with different Lorentz structures on the semileptonic $Λ_b \to Λ_c τ\barν_τ$ decay. This decay is of interest in light of the $R({D^{(*)}})$ puzzle in the semileptonic $\bar{B} \to D^{(*)} τ{\barν}_τ$ decays. In this work we add tensor operators to extend our previous results and consider both model-independent new physics (NP) and specific classes of models proposed to address the $R({D^{(*)}})$ puzzle. We show that a measurement of $R(Λ_c) = {\cal B}[Λ_b \to Λ_c τ\barν_τ] / {\cal B}[Λ_b \to Λ_c \ell \barν_{\ell}]$ can strongly constrain the NP parameters of models discussed for the $R({D^{(*)}})$ puzzle. We use form factors from lattice QCD to calculate all $Λ_b \to Λ_c τ\barν_τ$ observables. The $Λ_b \to Λ_c$ tensor form factors had not previously been determined in lattice QCD, and we present new lattice results for these form factors here.

hep-ph↗

Determination of mass hierarchy with $ν_μ\to ν_τ$ appearance and the effect of nonstandard interactions

Crucial developments in neutrino physics would be the determination of the mass hierarchy (MH) and measurement of the CP phase in the leptonic sector. The patterns of the transition probabilities $P(ν_μ\rightarrow ν_τ)$ and $P(\barν_μ\rightarrow \barν_τ)$ are sensitive to these oscillation parameters. An asymmetry parameter can be defined as the difference of these two probabilities normalized to their sum. The profile of the asymmetry parameter gives a clear signal of the mass ordering as it is found to be positive for inverted hierarchy and negative for normal hierarchy. The asymmetry parameter is also sensitive to the CP phase. We consider the effects of non-standard neutrino interactions (NSI) on the determination of the mass hierarchy. Since we assume the largest new physics effects involve the $τ$ sector only, we ignore NSI in production and study the NSI effects in detection as well as along propagation. We find that the NSI effects can significantly modify the prediction of the asymmetry parameter though the MH can still be resolved.

hep-ph↗

Probing lepton non-universality in tau neutrino Scattering

Recently hints of lepton flavor non-universality emerged in the BaBar and LHCb experiments. In this paper we propose tests of lepton universality in $ν_τ$ scattering. To parametrize the new physics we adopt an effective Lagrangian approach and consider the neutrino deep inelastic scattering processes $ν_τ+ N \to τ+ X$ and $ν_μ+ N \to μ+ X$ where we assume the largest new physics effects are in the $τ$ sector. We also consider an explicit leptoquark model in our calculations. In order to make comparison with the standard model and also in order to cancel out the uncertainties of the parton distribution functions, we consider the ratio of total and differential cross sections of tau-neutrino to muon-neutrino scattering. We find new physics effects that can possibly be observed at the proposed Search for Hidden Particles (SHiP) experiment at CERN.

hep-ph↗

Nonstandard interactions of tau neutrino via charged Higgs and $W'$ contribution

We consider charged Higgs and $W'$ gauge boson contributions to the quasielastic scattering $ν_τ+ n \rightarrow τ^- + p$ and $\barν_τ+ p \rightarrow τ^+ + n$ . These effects modify the standard model cross section for these processes and thus impact the extraction of the neutrino mixing angles $θ_{23}$ and $θ_{13}$ . We include form factor effects in our calculations and find the deviation of the actual mixing angle from the measured one, assuming the standard model cross section, can be significant and can depend on the energy of the neutrino.

hep-ph↗

Tau neutrino as a probe of nonstandard interaction

We study the $Δ$-resonance and deep inelastic scattering contributions in the tau-neutrino nucleon scattering $ν_τ+ N \to τ^- + X$ and $\barν_τ+ N \to τ^+ + X$ in the presence of a charged Higgs and a $W'$ gauge boson. The new physics effects to the quasielastic process have been discussed in a previous work. The extractions of the atmospheric mixing angle $θ_{23}$ rely on the standard model cross sections for $ν_τ+ N \to τ^- + X$ in $ν_τ$ appearance experiments. Corrections to the cross sections from the charged Higgs and $W'$ contributions modify the measured mixing angle. We include form factor effects in the new physics calculations and find the deviations of the mixing angle. If high-energy Long Base Line experiments are designed to measure $θ_{13}$ through tau neutrino appearance, the new physics effects to $ν_τ+ N \to τ^- + X$ and $\barν_τ+ N \to τ^+ + X$ can impact the extraction of this mixing angle. Finally, we investigate the new physics effects on the polarization of the $τ^\mp$ leptons produced in $ν_τ(\barν_τ)$ nucleon scattering.

hep-ph↗

Tau neutrino as a probe of nonstandard interactions via charged Higgs and $W'$ contribution

We discuss the impact of the presence of a charged Higgs and a $W'$ gauge boson on the tau-neutrino nucleon scattering $ν_τ+ N \rightarrow τ^- + X$ and $\barν_τ+ N \rightarrow τ^+ + X$. We show the effect of the new physics on the three subprocesses quasielastic, $Δ$-resonance, and deep inelastic scattering. The measurement of the atmospheric and reactor mixing angles $θ_{23}$ and $θ_{13}$, respectively, relies on the standard model cross section of the above processes if they have been measured in the appearance channels $ν_μ\rightarrow ν_τ$ and $\barν_e \rightarrow \barν_τ$ ($ν_e \rightarrow ν_τ$), respectively. Consideration of the new physics contributions to those reactions modifies the measured mixing angles, assuming the standard model cross section. We include form factor effects in the new physics calculations and find the deviations of the mixing angles which can be significant and can depend on the energy of the neutrino.

hep-ph↗

Deviation from Tri-Bimaximal Mixing and Large Reactor Mixing Angle

Recent observations for a non-zero $θ_{13}$ have come from various experiments. We study a model of lepton mixing with a 2-3 flavor symmetry to accommodate the sizable $θ_{13}$ measurement. In this work, we derive deviations from the tri-bimaximal (TBM) pattern arising from breaking the flavor symmetry in the neutrino sector, while the charged leptons contribution has been discussed in a previous work. Contributions from both sectors towards accommodating the non-zero $θ_{13}$ measurement are presented.

hep-ph↗

Radiative Scaling Neutrino Mass with $A_4$ Symmetry

A new idea for neutrino mass was proposed recently, where its smallness is not due to the seesaw mechanism, i.e. not inversely proportional to some large mass scale. It comes from a one-loop mechanism with dark matter in the loop consisting of singlet Majorana fermions $N_i$ with masses of order 10 keV and neutrino masses are scaled down from them by factors of about $10^{-5}$. We discuss how this model may be implemented with the non-Abelian discrete symmetry $A_4$ for neutrino mixing, and consider the phenomenology of $N_i$ as well as the extra scalar doublet $(η^+,η^0)$.

hep-ph↗

Scotogenic $A_4$ Neutrino Model for Nonzero $θ_{13}$ and Large $δ_{CP}$

Assuming that neutrinos acquire radiative seesaw Majorana masses through their interactions with dark matter, i.e. scotogenic from the Greek 'scotos' meaning darkness, and using the non-Abelian discrete symmetry $A_4$, we propose a model of neutrino masses and mixing with nonzero $θ_{13}$ and necessarily large leptonic CP violation, allowing both the normal and inverted hierarchies of neutrino masses, as well as quasi-degenerate solutions.

hep-ph↗

The charged lepton mass matrix and non-zero $θ_{13}$ with TeV scale New Physics

We provide an explicit structure of the charged lepton mass matrix which is 2-3 symmetric except for a single breaking of this symmetry by the muon mass. We identify a flavor symmetric limit for the mass matrices where the first generation is decoupled from the other two in the charged lepton sector while in the neutrino sector the third generation is decoupled from the first two generations. The leptonic mixing in the symmetric limit can be, among other structures, the bi-maximal (BM) or the tri-bimaximal (TBM) mixing. Symmetry breaking effects are included both in the charged lepton and the neutrino sector to produce corrections to the leptonic mixing and explain the recent $θ_{13}$ measurements. A model that extends the SM by three right handed neutrinos, an extra Higgs doublet, and two singlet scalars is introduced to generate the leptonic mixing.

hep-ph↗

The Top Forward Backward Asymmetry with general Z ' couplings

The measurement of the top forward-backward asymmetry in $\ttbar$ production measured at the Tevatron shows deviation from the Standard Model prediction. A $ u \to t$ transition via a flavor changing $Z^{\prime}$ can explain the data. We show that left handed $t_Lu_LZ^{\prime}$ couplings can be constrained from $B_{d,s}$ mixing while the constrains on the right handed couplings $t_R u_R Z^{\prime}$ vanish in the limit of $m_u \to 0$. We then consider the most general form of the $t uZ^{\prime}$ interaction which includes vector-axial vector as well as tensor type couplings and study how these couplings affect the top forward-backward asymmetry.

hep-ph↗

Probing light pseudoscalar, axial vector states through $η_{b} \toτ^{+}τ^{-}$

In this paper we explore the decay $η_b --> τ^+ τ^-$ as a probe for a light pseudoscalar or a light axial vector state. We estimate the standard model branching ratio for this decay to be $~4\times 10^{-9}$. We show that considerably larger branching ratios, up to the present experimental limit of ~8%, is possible in models with a light pseudoscalar or a light axial vector state. As we do not include possible mixing effects between the light pseudoscalar and the $η_b$, our results should be reliable when the pseudoscalar mass is away from the $η_b$ mass.

hep-ph↗