Publications (174)655.31 Total impact
 [Show abstract] [Hide abstract]
ABSTRACT: Using the fact that the neutrino mixing matrix , where and result from the diagonalisation of the charged lepton and neutrino mass matrices, we consider a number of forms of associated with a variety of flavour symmetries: i) bimaximal (BM) and ii) tribimaximal (TBM) forms, the forms corresponding iii) to the conservation of the lepton charge (LC), iv) to golden ratio type A (GRA) mixing, v) golden ratio type B (GRB) mixing, and vi) to hexagonal (HG) mixing. Employing the minimal form of , in terms of angles and phases it contains, that can provide the requisite corrections to so that reactor, atmospheric and solar neutrino mixing angles , and have values compatible with the current data, including a possible sizable deviation of from , we discuss the possibility to obtain predictions for the CP violation phases in the neutrino mixing matrix. Considering the “standard ordering” of the the 12 and the 23 rotations in and following the approach developed in [1] we derive predictions for the Dirac phase δ and the rephasing invariant in the cases of GRA, GRB and HG forms of (results for the TBM and BM (LC) forms were obtained in [1]). We show also that under rather general conditions within the scheme considered the values of the Majorana phases in the PMNS matrix can be predicted for each of the forms of discussed. We give examples of these predictions and of their implications for neutrinoless double beta decay. In the GRA, GRB and HG cases, as in the TBM one, relatively large CP violation effects in neutrino oscillations are predicted ( ). Distinguishing between the TBM, BM (LC), GRA, GRB and HG forms of requires a measurement of or a relatively high precision measurement of .Nuclear Physics B. 01/2015;  [Show abstract] [Hide abstract]
ABSTRACT: The process of Radiative Emission of Neutrino Pair (RENP) in atoms is sensitive to the absolute neutrino mass scale, the type of spectrum neutrino masses obey and the nature  Dirac or Majorana  of massive neutrinos. We analyse the possibility to test the hypothesis of existence of neutrinos with masses at the eV scale coupled to the electron in the weak charged lepton current in an RENP experiment. The presence of eV scale neutrinos in the neutrino mixing is associated with the existence of sterile neutrinos which mix with the active flavour neutrinos. At present there are a number of hints for activesterile neutrino oscillations driven by $\Delta m^2 \sim 1~{\rm eV^2}$. We perform a detailed analysis of the RENP phenomenology within the "3 + 1" scheme with one sterile neutrino.Physics Letters B. 11/2014; 742.  [Show abstract] [Hide abstract]
ABSTRACT: Using the fact that the neutrino mixing matrix $U = U^\dagger_{e}U_{\nu}$, where $U_{e}$ and $U_{\nu}$ result from the diagonalisation of the charged lepton and neutrino mass matrices, we analyse the sum rules which the Dirac phase $\delta$ present in $U$ satisfies when $U_{\nu}$ has a form dictated by flavour symmetries and $U_e$ has a "minimal" form (in terms of angles and phases it contains) that can provide the requisite corrections to $U_{\nu}$, so that reactor, atmospheric and solar neutrino mixing angles $\theta_{13}$, $\theta_{23}$ and $\theta_{12}$ have values compatible with the current data. The following symmetry forms are considered: i) tribimaximal (TBM), ii) bimaximal (BM) (or corresponding to the conservation of the lepton charge $L' = L_e  L_\mu  L_{\tau}$ (LC)), iii) golden ratio type A (GRA), iv) golden ratio type B (GRB), and v) hexagonal (HG). We investigate the predictions for $\delta$ in the cases of TBM, BM (LC), GRA, GRB and HG forms using the exact and the leading order sum rules for $\cos\delta$ proposed in the literature, taking into account also the uncertainties in the measured values of $\sin^2\theta_{12}$, $\sin^2\theta_{23}$ and $\sin^2\theta_{13}$. This allows us, in particular, to assess the accuracy of the predictions for $\cos\delta$ based on the leading order sum rules and its dependence on the values of the indicated neutrino mixing parameters when the latter are varied in their respective 3$\sigma$ experimentally allowed ranges.10/2014; 
Article: The Daya Bay and T2K results on $\sin^2 2 \theta_{13}$ and NonStandard Neutrino Interactions
[Show abstract] [Hide abstract]
ABSTRACT: We show that the relatively large best fit value of $\sin^2 2 \theta_{13} = 0.14 \, (0.17)$ measured in the T2K experiment for fixed values of i) the Dirac CP violation phase $\delta = 0$, and ii) the atmospheric neutrino mixing parameters $\theta_{23} = \pi/4$, $\Delta m^2_{32} = 2.4 \times 10^{3} \; {\rm eV}^2$, can be reconciled with the Daya Bay result $\sin^2 2 \theta_{13} = 0.090 \pm 0.009$ if the effects of nonstandard neutrino interactions (NSI) in the relevant $\bar \nu_e \to \bar \nu_e$ and $\nu_\mu \to \nu_e$ oscillation probabilities are taken into account.05/2014;  [Show abstract] [Hide abstract]
ABSTRACT: The phenomenology of 3neutrino mixing, the current status of our knowledge about the 3neutrino mixing parameters, including the absolute neutrino mass scale, and of the Dirac and Majorana CP violation in the lepton sector, are reviewed. The problems of CP violation in neutrino oscillations and of determining the nature — Dirac or Majorana — of massive neutrinos, are discussed. The seesaw mechanism of neutrino mass generation and the related leptogenesis scenario of generation of the baryon asymmetry of the universe, are considered. The results showing that the CP violation necessary for the generation of the baryon asymmetry of the universe in leptogenesis can be due exclusively to the Dirac and/or Majorana CPviolating phase(s) in the neutrino mixing matrix U, are briefly reviewed.International Journal of Modern Physics A 03/2014; 29(11n12). · 1.09 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We discuss how two birds—the little hierarchy problem of lowscale typeI seesaw models and the search for a viable dark matter candidate—are (proverbially) killed by one stone: a new inert scalar state.European Physical Journal C 01/2014; 74(2). · 5.44 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We show that the relatively large best fit value of sin22θ13=0.14(0.17) measured in the T2K experiment for fixed values of i) the Dirac CP violation phase δ=0δ=0, and ii) the atmospheric neutrino mixing parameters θ23=π/4θ23=π/4, Δm322=2.4×10−3 eV2, can be reconciled with the Daya Bay result sin22θ13=0.090±0.009 if the effects of nonstandard neutrino interactions (NSI) in the relevant ν¯e→ν¯e and νμ→νeνμ→νe oscillation probabilities are taken into account.Nuclear Physics B. 01/2014; 886:31–42.  [Show abstract] [Hide abstract]
ABSTRACT: We analyse the interplay of generalised CP transformations and the nonAbelian discrete group $T^{\prime}$ and use the semidirect product $G_f= T^{\prime}\rtimes H_{\text{CP}}$, as family symmetry acting in the lepton sector. The family symmetry is shown to be spontaneously broken in a geometrical manner. In the resulting flavour model, naturally small Majorana neutrino masses for the light active neutrinos are obtained through the type I seesaw mechanism. The known masses of the charged leptons, lepton mixing angles and the two neutrino mass squared differences are reproduced by the model with a good accuracy. The model allows for two neutrino mass spectra with normal ordering (NO) and one with inverted ordering (IO). For each of the three spectra the absolute scale of neutrino masses is predicted with relatively small uncertainty. The value of the Dirac CP violation (CPV) phase $\delta$ in the lepton mixing matrix is predicted to be $\delta \cong \pi/2~{\rm or}~ 3\pi/2$. Thus, the CP violating effects in neutrino oscillations are predicted to be maximal (given the values of the neutrino mixing angles) and experimentally observable. We present also predictions for the sum of the neutrino masses, for the Majorana CPV phases and for the effective Majorana mass in neutrinoless double beta decay. The predictions of the model can be tested in a variety of ongoing and future planned neutrino experiments.Journal of High Energy Physics 12/2013; 2014(2). · 6.22 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We perform a detailed analysis of lepton flavour violation (LFV) within minimal seesaw type extensions of the Standard Model (SM), which give a viable mechanism of neutrino mass generation and provide new particle content at the electroweak scale. We focus, mainly, on predictions and constraints set on each scenario from μ → eγ, μ → 3e and μ − e conversion in the nuclei. In this class of models, the flavour structure of the Yukawa couplings between the additional scalar and fermion representations and the SM leptons is highly constrained by neutrino oscillation measurements. In particular, we show that in some regions of the parameters space of type I and type II seesaw models, the Dirac and Majorana phases of the neutrino mixing matrix, the ordering and hierarchy of the active neutrino mass spectrum as well as the value of the reactor mixing angle θ 13 may considerably affect the size of the LFV observables. The interplay of the latter clearly allows to discriminate among the different low energy seesaw possibilities.Journal of High Energy Physics 09/2013; 2012(8). · 6.22 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We investigate the predictions for neutrinoless double beta ($(\beta \beta)_{0 \nu}$) decay effective Majorana mass $\left \langle \, m \, \rangle \right$ in the 3+1 and 3+2 schemes with one and two additional sterile neutrinos with masses at the eV scale. The two schemes are suggested by the neutrino oscillation interpretation of the reactor neutrino and Gallium "anomalies" and of the data of the LSND and MiniBooNE experiments. We analyse in detail the possibility of a complete or partial cancellation between the different terms in $\left \langle \, m \, \rangle \right$, leading to a strong suppression of $\left \langle \, m \, \rangle \right$. We determine the regions of the relevant parameter spaces where such a suppression can occure. This allows us to derive the conditions under which the effective Majorana mass satisfies $\left \langle \, m \, \rangle \right > 0.01$ eV, which is the range planned to be exploited by the next generation of $(\beta \beta)_{0 \nu}$experiments.08/2013;  [Show abstract] [Hide abstract]
ABSTRACT: The lepton flavour violating (LFV) $\tau$ decays $\tau\to (e,\mu)\gamma$ and $\tau\to 3\mu$ are investigated in the frameworks of the TeV scale type I seesaw and Higgs Triplet (or type II seesaw) models. Predictions for the rates of these processes are obtained. The implications of the existing stringent experimental upper bounds on the $\mu\to e + \gamma$ and $\mu\to 3e$ decay branching ratios for the predictions of the $\tau\to (e,\mu)\gamma$ and $\tau\to 3\mu$ decay rates are studied in detail. The possibilities to observe the indicated LFV $\tau$ decays in present and future experiments are analysed.Journal of High Energy Physics 08/2013; · 6.22 Impact Factor 
Article: The Nature of Massive Neutrinos
[Show abstract] [Hide abstract]
ABSTRACT: The compelling experimental evidences for oscillations of solar, reactor, atmospheric, and accelerator neutrinos imply the existence of 3neutrino mixing in the weak charged lepton current. The current data on the 3neutrino mixing parameters are summarised and the phenomenology of 3 mixing is reviewed. The properties of massive Majorana neutrinos and of their various possible couplings are discussed in detail. Two models of neutrino mass generation with massive Majorana neutrinos—the type I seesaw and the Higgs triplet model—are briefly reviewed. The problem of determining the nature, Dirac or Majorana, of massive neutrinos is considered. The predictions for the effective Majorana mass in neutrinoless doublebeta() decay in the case of 3neutrino mixing and massive Majorana neutrinos are summarised. The physics potential of the experiments, searching for decay for providing information on the type of the neutrino mass spectrum, on the absolute scale of neutrino masses, and on the Majorana CPviolation phases in the PMNS neutrino mixing matrix, is also briefly discussed. The opened questions and the main goals of future research in the field of neutrino physics are outlined.Advances in High Energy Physics 04/2013; 2013. · 2.62 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We investigate the possibility to discriminate between different pairs of CP nonconserving mechanisms inducing the neutrinoless double beta $\betabeta$decay by using data on $\betabeta$decay halflives of nuclei with largely different nuclear matrix elements (NMEs). The mechanisms studied are: light Majorana neutrino exchange, heavy lefthanded (LH) and heavy righthanded (RH) Majorana neutrino exchanges, lepton charge nonconserving couplings in SUSY theories with Rparity breaking giving rise to the "dominant gluino exchange" and the "squarkneutrino" mechanisms. The nuclei considered are $^{76}$Ge, $^{82}$Se, $^{100}$Mo, $^{130}$Te and $^{136}$Xe. Four sets of nuclear matrix elements (NMEs) of the decays of these five nuclei, derived within the Selfconsistent Renormalized Quasiparticle Random Phase Approximation (SRQRPA), were employed in our analysis. While for each of the five single mechanisms discussed, the NMEs for $^{76}$Ge, $^{82}$Se, $^{100}$Mo and $^{130}$Te differ relatively little, the relative difference between the NMEs of any two nuclei not exceeding 10%, the NMEs for $^{136}Xe$ differ significantly from those of $^{76}$Ge, $^{82}Se$, $^{100}$Mo and $^{130}$Te, being by a factor $\sim (1.3  2.5)$ smaller. This allows, in principle, to draw conclusions about the pair of noninterfering (interfering) mechanisms possibly inducing the $\betabeta$decay from data on the halflives of $^{136}Xe$ and of at least one (two) more isotope(s) which can be, e.g., any of the four, $^{76}Ge$, $^{82}Se$, $^{100}Mo$ and $^{130}Te$. Depending on the sets of mechanisms considered, the conclusion can be independent of, or can depend on, the NMEs used in the analysis. The implications of the EXO lower bound on the halflife of $^{136}Xe$ for the problem studied are also exploited.Journal of High Energy Physics 12/2012; 2013(2). · 6.22 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We present a SUSY SU(5)×T′ unified flavor model with type I seesaw mechanism of neutrino mass generation, which predicts the reactor neutrino angle to be θ13≈0.14 close to the recent results from the Daya Bay and RENO experiments. The model predicts also values of the solar and atmospheric neutrino mixing angles, which are compatible with the existing data. The T′ breaking leads to tribimaximal mixing in the neutrino sector, which is perturbed by sizeable corrections from the charged lepton sector. The model exhibits geometrical CP violation, where all complex phases have their origin from the complex ClebschGordan coefficients of T′. The values of the Dirac and Majorana CP violating phases are predicted. For the Dirac phase in the standard parametrization of the neutrino mixing matrix we get a value close to 90°: δ≅π/20.45θc≅84.3°, θc being the Cabibbo angle. The neutrino mass spectrum can be with normal ordering (2 cases) or inverted ordering. In each case the values of the three light neutrino masses are predicted with relatively small uncertainties, which allows one to get also unambiguous predictions for the neutrinoless double beta decay effective Majorana mass.Physical review D: Particles and fields 12/2012; 86(11).  [Show abstract] [Hide abstract]
ABSTRACT: The process of collective deexcitation of atoms in a metastable level into emission mode of a single photon plus a neutrino pair, called radiative emission of neutrino pair (RENP), is sensitive to the absolute neutrino mass scale, to the neutrino mass hierarchy and to the nature (Dirac or Majorana) of massive neutrinos. We investigate how the indicated neutrino mass and mixing observables can be determined from the measurement of the corresponding continuous photon spectrum taking the example of a transition between specific levels of the Yb atom. The possibility of determining the nature of massive neutrinos and, if neutrinos are Majorana fermions, of obtaining information about the Majorana phases in the neutrino mixing matrix, is analyzed in the cases of normal hierarchical, inverted hierarchical and quasidegenerate types of neutrino mass spectrum. We find, in particular, that the sensitivity to the nature of massive neutrinos depends critically on the atomic level energy difference relevant in the RENP.Physics Letters B 09/2012; 719(s 1–3). · 6.02 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: The couplings of the low scale type I seesaw model are severely constrained by the requirement of reproducing the correct neutrino mass and mixing parameters, by the nonobservation of lepton number and charged lepton flavour violating processes and by electroweak precision data. We show that all these constraints still allow for the possibility of an exotic Higgs decay channel into a light neutrino and a heavy neutrino with a sizable branching ratio. We also estimate the prospects to observe this decay at the LHC and discuss its complementarity to the indirect probes of the low scale type I seesaw model from experiments searching for the $\mu\to e\gamma$ decay.Physics Letters B 08/2012; 718(3). · 6.02 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We perform a detailed analysis of lepton flavour violation (LFV) within minimal seesaw type extensions of the Standard Model (SM), which give a viable mechanism of neutrino mass generation and provide new particle content at the electroweak scale. We focus, mainly, on predictions and constraints set on each scenario from mu > e gamma, mu > 3e and mu  e conversion in the nuclei. In this class of models, the flavour structure of the Yukawa couplings between the additional scalar and fermion representations and the SM leptons is highly constrained by neutrino oscillation measurements. In particular, we show that in some regions of the parameters space of type I and type II seesaw models, the Dirac and Majorana phases of the neutrino mixing matrix, the ordering and hierarchy of the active neutrino mass spectrum as well as the value of the reactor mixing angle theta_{13} may considerably affect the size of the LFV observables. The interplay of the latter clearly allows to discriminate among the different low energy seesaw possibilities.05/2012;  [Show abstract] [Hide abstract]
ABSTRACT: We investigate the generation of the baryon asymmetry of the Universe within a SUSY SU(5) x T' model of flavour, which gives rise to realistic masses and mixing patterns for quarks and leptons. The model employs the seesaw mechanism for generation of the light neutrino masses and the baryon asymmetry is produced via leptogenesis. We perform detailed calculations of both the CP violating lepton asymmetries, originating from the decays of the heavy Majorana neutrinos operative in the seesaw mechanism, and of the efficiency factors which account for the lepton asymmetry washout processes in the Early Universe. The latter are calculated by solving numerically the system of Boltzmann equations describing the generation and the evolution of the lepton asymmetries. The baryon asymmetry in the model considered is proportional to the J_{CP} factor, which determines the magnitude of CP violation effects in the oscillations of flavour neutrinos. The leptogenesis scale can be sufficiently low, allowing to avoid the potential gravitino problem.Physics Letters B 03/2012; 710(3). · 6.02 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We obtain predictions for the neutrino masses, the effective Majorana mass in neutrinoless double beta decay and for the rates of the lepton flavor violating processes $\mu\rightarrow e + \gamma$, $\tau \rightarrow e + \gamma$ and $ \tau \rightarrow \mu + \gamma$ in a SUSY $SU(5) \times T^{\prime}$ Model of flavour, which gives rise to realistic masses and mixing patterns for quarks and leptons.09/2011;  [Show abstract] [Hide abstract]
ABSTRACT: We study a type I seesaw scenario where the righthanded (RH) neutrinos, responsible for the light neutrino mass generation, lie at the electroweak scale. Under certain conditions, the strength of the charged current (CC) and neutral current (NC) weak interactions of the standard model particles with the heavy RH neutrinos can be large enough to allow the production of the latter at the LHC, opening also the possibility of observing other low energy signatures of the new physics in the electroweak precision observables as well as in searches for rare leptonic decays or neutrinoless double beta decay. In this scenario the flavor structure of the indicated CC and NC couplings of the heavy RH neutrinos is essentially determined by the low energy neutrino parameters, leading to fairly strong correlations among the new phenomena. In particular, we show that the present bound on the μ→e+γ decay rate makes very difficult the observation of the heavy RH neutrinos at the LHC or the observation of deviations from the standard model predictions in the electroweak precision data. We also show that all present experimental constraints on this scenario still allow (i) for an enhancement of the rate of neutrinoless double beta decay, which thus can be in the range of sensitivity of the GERDA experiment even when the light Majorana neutrinos possess a normal hierarchical mass spectrum, and (ii) for the predicted μ→e+γ decay rate to be within the sensitivity range of the MEG experiment.Physical review D: Particles and fields 07/2011; 84(1).
Publication Stats
11k  Citations  
655.31  Total Impact Points  
Top Journals
Institutions

2010–2014

The University of Tokyo
Tōkyō, Japan


1981–2014

Bulgarian Academy of Sciences
 Institute for Nuclear Research and Nuclear Energy (INRNE)
Ulpia Serdica, SofiaCapital, Bulgaria


1991–2011

Scuola Internazionale Superiore di Studi Avanzati di Trieste
Trst, Friuli Venezia Giulia, Italy


2007

University of California, Berkeley
 Department of Physics
Berkeley, California, United States


1992–2007

INFN  Istituto Nazionale di Fisica Nucleare
Frascati, Latium, Italy


2003–2005

Abdus Salam International Centre for Theoretical Physics
Trst, Friuli Venezia Giulia, Italy


1994–2004

University of North Carolina at Chapel Hill
 Department of Physics and Astronomy
North Carolina, United States


2002

University of California, Los Angeles
 Department of Physics and Astronomy
Los Ángeles, California, United States 
Technische Universität Dortmund
Dortmund, North RhineWestphalia, Germany


2000

Medical University of Sofia
Ulpia Serdica, SofiaCapital, Bulgaria


1979–1993

CERN
 • Physics Department (PH)
 • Technology Department (TE)
Genève, Geneva, Switzerland


1987

Institute for Nuclear Research and Nuclear Energy
Ulpia Serdica, SofiaCapital, Bulgaria


1984

Joint Institute for Nuclear Research
Dubno, Moskovskaya, Russia


1983

University of Delaware
Delaware, United States
