arXiv subjects

E. I. Lashin

Publications and source records attributed to E. I. Lashin.

At least 19 recordsLinked to original sources

arXiv2025

Role of unphysical neutrino phases in the phenomenology of consistently defined textures. Case study: traceless neutrino mass matrix

We highlight the role played by the unphysical phases in the definition of neutrino mass matrix, showing it does not relate to mere semantics, rather it has an effect on the phenomenology. As a case study, we take the neutrino mass matrix texture characterized by a vanishing trace, and study the effect of the phases, physical and unphysical, in its definition. We undergo a thorough phenomenological analysis, first (second) when the unphysical (CP) phases are vanishing, then move on to the general case where all phases exist. We stress that the effect of the unphysical phases on the phenomenology originates from changing the texture definition upon introducing them, while they are not observable. Finally we present a theoretical realization of the texture based on $A_5$ non-abelian flavor symmetry, which is also related to a consistently defined texture.

hep-ph↗

arXiv2025

A preference for dynamical phantom dark energy using one-parameter model with Planck, DESI DR1 BAO and SN data

Baryon Acoustic Oscillation (BAO) provides a powerful tool to measure cosmic expansion and consequently the nature of the Dark Energy (DE). Recent precise BAO measurements by Dark Energy Spectroscopic Instrument data release 1 (DESI DR1), when combined with Cosmic Microwave Background (CMB) data from Planck and Supernovae of Type Ia (SN Ia), favor evolving dark energy over cosmological constant. This result is strongly related to the assumed priors on the Chevallier-Polarski-Linder (CPL) parameterization of DE. We test another parametrization which introduces two free parameters $n$ and $α$, only $n$ is independent. Thus, it reduces the parameter space compared to the CPL model, which derives a more robust preference for evolving DE, if any. The model potentially produces three cosmological scenarios according to the values of its parameters. For $n=3$, the $Λ$CDM model is recovered, quintessence for $n<3$, and phantom for $n>3$. In the present study, we test the model on the background level, and, to our knowledge for the first time, on the linear perturbation level. Bayesian evidence analysis shows a weak preference \textbf{($\mathbf{\ln B \leq 1.8}$)} for dynamical DE in the phantom regime over the cosmological constant DE using Planck, DESI, and PantheonPlus \& SH0ES data, similarly the AIC analysis supports dynamical DE scenario for the same data. The model predicts current phantom DE $w_{de,0} = -1.073 \pm 0.032$ and $H_0=70.9\pm 1.4$ km/s/Mpc when Planck+DESI data is used, which decreases the tension with $H_0$ local measurements to $1.2σ$ level.

astro-ph.CO↗

arXiv2024

Textures of Neutrino Mass Matrix from $S_4$-flavor Symmetry

We study a texture of neutrino mass matrix characterized by two constraints consisting of one equality and another antiequality between two elements corresponding to two pairs of the matrix entries. Amidst such textures, we limit our study to three patterns which were realizable assuming an $S_4$-symmetry within type II-seesaw scenario. Three such cases were found and studied: I ($M_{\n 22}=-M_{\n 33}$ \& $M_{\n 11}=+M_{\n 23}$), II ($M_{\n 11}=-M_{\n 33}$ \& $M_{\n 22}=+M_{\n 13}$) and III ($M_{\n 11}=-M_{\n 22}$ \& $M_{\n 33}=+M_{\n 12}$). We specify the role of unphysical phases in the definition of the textures under study which were tested against experimental constraints, and were found to accommodate data with both hierarchies allowed. However, switching off the unphysical phases allows only for inverted hierarchy, except for the texture III which allows also, albeit for a very narrow parameter space region, for normal ordering. We stress that the different phenomenologies when including/excluding unphysical phases stem from the different definitions of the texture one has to adopt in order to make it insensitive to unphysical phases, rather than to any `absent' physical effects of unphysical phases. We present a complete phenomenological analysis of these three textures and justify analytically the resulting correlations. We detail the effect of the unphysical phases in diluting/deforming several correlations, which otherwise would have been ``clear". Finally, we give theoretical realizations within seesaw type II scenarios for such textures.

hep-ph↗

arXiv2023

Texture of Two Vanishing Subtraces in Neutrino Mass Matrix and Current Experimental Tests

We present a full phenomenological and analytical study for the neutrino mass matrix characterized by two vanishing $2\times2$ subtraces. We update one past result in light of the recent experimental data. Out of the fifteen possible textures, we find seven cases can accommodate the experimental data instead of eight ones in the past study. We also introduce few symmetry realizations for viable and nonviable textures based on non-abelian ($A_4$ or $S_4$) flavor symmetry within type II seesaw scenario.

hep-ph↗

arXiv2021

Texture of One Equality in Neutrino Mass Matrix

We carry out a phenomenological and analytical study of the texture structures for the Majorana neutrino mass matrix characterized by one single equality between two independent matrix elements, with vanishing non-physical phases whose role in the definition we clarify. We find that fourteen textures are viable in both types of hierarchy, whereas the remaining fifteenth one is viable only in normal hierarchy. We also present symmetry realizations for some patterns by using Abelian flavor symmetries within type-I, type-II and mixed type-(I+II) seesaw scenarios.

hep-ph↗

arXiv2021

Texture of Single Vanishing Subtrace in Neutrino Mass Matrix

We consider a texture for the neutrino mass matrix characterized by one vanishing $2\times2$ subtrace. We analyze phenomenologically and analytically all the six possible patterns, and show that all non-singular ones are able to accommodate the experimental bounds, whereas singular patterns allow only for four inverted-hierarchy type textures. We then present some possible realizations of this texture, within seesaw scenarios, either directly or indirectly by relating it to zero-textures.

hep-ph↗

arXiv2020

Degenerate Bogdanov-Takens bifurcations in a bulk viscous cosmology

Using the dynamical system theory we show that the Friedmann-Robertson-Walker (FRW) cosmological model with bulk viscous fluid in the presence of cosmological constant is equivalent to a degenerate two dimensional Bogdanov-Takens normal form. The equation of state parameter, $ω$, the bulk viscosity coefficient, $ξ$, and the cosmological constant, $Λ$, define the necessary parameters for unfolding the degenerate Bogdanov-Takens system. The fixed points of the system are discussed together with the variation of their stability properties upon changing the relevant parameters $ω$, $Λ$ and $ξ$. The variation of the stability properties are visualized by the appropriate bifurcation diagrams. Phase portrait for finite domain and global phase portrait are displayed and the issue of the structural stability is discussed. Typical issues such as late acceleration or inflation that can be induced by viscosity and could have relevance to observational cosmology are also discussed.

gr-qc↗

arXiv2017

Rotated $μ$\,--\,$τ$ Symmetry for One Generic Neutrino Mixing Angle: An analytical Study

We find a realization of the $Z_2$-symmetry in the neutrino mass matrix which expresses a rotation of the $μ-τ$ symmetry and is able to impose a generic smallest mixing angle, in contrast to a zero-value predicted by the usual non-rotated form of the $μ-τ$ symmetry. We extend this symmetry for the lepton sector within type-I seesaw scenario, and show it can accommodate the mixing angles, the mass hierarchies and the lepton asymmetry in the universe. We then study the effects of perturbing the specific form of the neutrino mass matrix imposed by the symmetry and compute the resulting mixing and mass spectrum. We trace back this "low-scale" perturbation to a "high-scale" perturbation, and find realizations of this latter one arising from exact symmetries with an enriched matter content.

hep-ph↗

arXiv2017

Comment on "Quantum Raychaudhuri equation"

We address the validity of the formalism and results presented in [ S. Das, Phys. Rev. {\bf D89} 084068 (2014)] with regard to quantum Raychaudhuri equation. The author obtained the so called quantum Raychaudhuri equation by replacing classical geodesics with quantal trajectories arising from Bhommian mechanics. The resulting modified equation was used to draw some conclusions about the inevitability of focussing and the formation of conjugate points and therefore singularity. We show that the whole procedure is full of problematic points, on both physical relevancy and mathematical correctness. In particular, we illustrate the problems associated with the technical derivation of the so called quantum Raychaudhuri equation, as well as its invalid physical implications.

gr-qc↗

arXiv2015

Neutrino Mixing and Leptogenesis in $μ-τ$ Symmetry

We study the consequences of the $Z_2$-symmetry behind the $μ$--$τ$ universality in neutrino mass matrix. We then implement this symmetry in the type-I seesaw mechanism and show how it can accommodate all sorts of lepton mass hierarchies and generate enough lepton asymmetry to interpret the observed baryon asymmetry in the universe. We also show how a specific form of a high-scale perturbation is kept when translated via the seesaw into the low scale domain, where it can accommodate the neutrino mixing data. We finally present a realization of the high scale perturbed texture through addition of matter and extra exact symmetries.

hep-ph↗

arXiv2015

On the correctness of cosmology from quantum potential

We examine in detail the cosmology based on quantal (Bohmian) trajectories as suggested in a recent study arXiv:1404.3093[gr-qc]. We disagree with the conclusions regarding predicting the value of the cosmological constant $Λ$ and evading the big bang singularity. Furthermore, we show that the approach of using a quantum corrected Raychaudhuri equation (QRE), as suggested in arXiv:1404.3093[gr-qc], is unsatisfactory, because, essentially, it uses the Raychaudhuri equation, which is a kinematical equation, in order to predict dynamics. In addition, even within this inconsistent framework, the authors have adopted unjustified assumptions and carried out incorrect steps leading to doubtful conclusions.

gr-qc↗

arXiv2014

Neutrino Mass Textures and Partial $μ$-$τ$ Symmetry

We discuss the viability of the $μ$--$τ$ interchange symmetry imposed on the neutrino mass matrix in the flavor space. Whereas the exact symmetry is shown to lead to textures of completely degenerate spectrum which is incompatible with the neutrino oscillation data, introducing small perturbations into the preceding textures, inserted in a minimal way, lead however to four deformed textures representing an approximate $μ$--$τ$ symmetry. We motivate the form of these `minimal' textures, which disentangle the effects of the perturbations, and present some concrete realizations assuming exact $μ$--$τ$ at the Lagrangian level but at the expense of adding new symmetries and matter fields. We find that all these deformed textures are capable to accommodate the experimental data, and in all types of neutrino mass hierarchies, in particular the non-vanishing value for the smallest mixing angle.

hep-ph↗

arXiv2013

Two driven coupled qubits in a time varying magnetic field: exact and approximate solutions

We study the dynamics of a two-qubit system coupled through time dependent anisotropic $XYZ$ Heisenberg interaction in presence of a time varying non-uniform external magnetic field. Exact results are presented for the time evolution of the system under certain integrability conditions. Furthermore, the corresponding entanglement of the system is studied for different values of the involved parameters. We found that the time evolution and different properties of entanglement such as amplitude, frequency and profile can be finely tuned by the interplay of the characteristics of the time-dependent magnetic field and exchange coupling. Also we show how the discrete symmetries of the system Hamiltonian, which splits its Hilbert space into two distinct subspaces, can be utilized to deduce the dynamics in one of its two distinct subspaces from the other one. Moreover, approximate results for the time evolution are provided utilizing the rotating wave as well as the perturbation approximations for the special case of either static magnetic field or exchange coupling. We compare the range of validity of the two approximation methods and their effectiveness in treating the considered system and determine their critical parameters.

quant-ph↗

arXiv2012

The U(1) symmetry of the non-tribimaximal pattern in the degenerate mass spectrum case of the neutrino mass matrix

On account of the new neutrino oscillation data signalling a non-zero value for the smallest mixing angle ($θ_z$), we present an explicit realization of the underlying U(1) symmetry characterizing the maximal atmospheric mixing angle ($θ_y = π/ 4$) pattern with two degenerate masses but now with generic values of $θ_z$. We study the effects of the form invariance with respect to U(1), and/or $Z_3$, $Z_2$ subgroups, on the Yukawa couplings and the mass terms. Later on, we specify $θ_z$ to its experimental best fit value ($ \sim 8^o$), and impose the symmetry in an entire model which includes charged leptons, and many Higgs doublets or standard model singlet heavy scalars, to show that it can make room for the charged lepton mass hierarchies. In addition, we show for the non-tribimaximal value of $θ_z \neq 0$ within type-I seesaw mechanism enhanced with flavor symmetry that neutrino mass hierarchies can be generated. Furthermore, lepton/baryogenesis can be interpreted via type-II seesaw mechanism within a setup meeting the flavor U(1)-symmetry.

hep-ph↗

arXiv2012

The (Z_2)^3 symmetry of the non-tri-bimaximal pattern for the neutrino mass matrix

In view of the recent neutrino oscillation data pointing to a non-vanishing value for the smallest mixing angle ($θ_z$), we derive and find explicit realizations of the $(Z_2)^3$ flavor symmetry which characterizes, for the neutrino mass matrix, uniquely a variant of the tripartite form, originally conceived to lead to the tri-bimaximal mixing with $θ_z=0$, so that to allow now for a non-tri-bimaximal pattern with non-zero $θ_z$. We impose this flavor symmetry in a setting including the charged leptons and we see that it can make room, through higher order terms involving new SM-singlet scalars, for the mass hierarchy of charged leptons. Moreover, within type-I seesaw mechanism augmented with the flavor symmetry, certain patterns occurring in both the Dirac and the Majorana neutrino mass matrices can accommodate all types of mass hierarchies in the effective neutrino mass matrix, but no lepton/baryon asymmetry can be generated. Finally, we discuss how type-II seesaw mechanism, when supplemented with the flavor symmetry, could be used to interpret the observed baryon asymmetry through leptogenesis.

hep-ph↗

arXiv2012

The One-zero Textures of Majorana Neutrino Mass Matrix and Current Experimental Tests

We carry out a complete and systematic study of all the possible one-zero textures for the neutrino mass matrix in light of the recent neutrino oscillation data which hint to a relatively large non-vanishing value for the smallest mixing angle ($θ_z$). We find that all the six possible one-zero textures are able to accommodate the experimental data, with five cases allowing also for non-invertible mass matrices. We present symmetry realizations for all the one-zero singular and non-singular patterns in type-I and type-II seesaw mechanism schemes.

hep-ph↗

arXiv2010

Form Invariance and Symmetry in the Neutrino Mass Matrix

We present the general form of the unitary matrices keeping invariant the Majorana neutrino mass matrix of specific texture suitable for explaining oscillation data. In the case of the Tri-bimaximal pattern with two degenerate masses we give a specific realization of the underlying $U(1)$ symmetry which can be uplifted to a symmetry in a complete theory including charged leptons. For this, we present a model with three light SM-like Higgs doublets and one heavy Higgs triplet and find that one can accommodate the hierarchy of the charged lepton masses. The lepton mass spectrum can also be achieved in another model extending the SM with three SM-singlet scalars transforming non trivially under the flavor symmetry. We discuss how such a model has room for generating enough baryon asymmetry through leptogenesis in the framework of Type-I and II seesaw mechanisms.

hep-ph↗

arXiv2009

(Z_2)^3 Symmetry of the Tripartite Model

We derive in a simple way the $(Z_2)^3$ symmetry which characterizes uniquely the phenomenologically successful tripartite form leading to the tribimaximal mixing in the neutrino mass matrix. We impose this symmetry in a setup including the charged leptons and find that it can accommodate all the possible patterns of lepton masses in the framework of type-I and type-II seesaw mechanisms. We also discuss the possibility of generating enough baryon asymmetry through lepton-lepton asymmetry.

hep-ph↗