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Probir Roy

Publications and source records attributed to Probir Roy.

At least 37 records · Page 2Linked to original sources
arXiv2011

Neutrino masses, cosmological bound and four zero Yukawa textures

Four zero neutrino Yukawa textures in a specified weak basis, combined with $μτ$ symmetry and type-I seesaw, yield a highly constrained and predictive scheme. Two alternately viable $3\times3$ light neutrino Majorana mass matrices $m_{νA}/m_{νB}$ result with inverted/normal mass ordering. Neutrino masses, Majorana in character and predicted within definite ranges with laboratory and cosmological inputs, will have their sum probed cosmologically. The rate for $0νββ$ decay, though generally below the reach of planned experiments, could approach it in some parameter region. Departure from $μτ$ symmetry due to RG evolution from a high scale and consequent CP violation, with a Jarlskog invariant whose magnitude could almost reach $6\times 10^{-3}$, are explored.

hep-ph↗
arXiv2011

Baryon asymmetry from leptogenesis with four zero neutrino Yukawa textures

The generation of the right amount of baryon asymmetry $η$ of the Universe from supersymmetric leptogenesis is studied within the type-I seesaw framework with three heavy singlet Majorana neutrinos $N_i\,\,(i = 1,2,3)$ and their superpartners. We assume the occurrence of four zeroes in the neutrino Yukawa coupling matrix $Y_ν$, taken to be $μτ$ symmetric, in the weak basis where $N_i$ (with real masses $M_i>0$) and the charged leptons $l_α\,\, (α= e,μ,τ)$ are mass diagonal. The quadrant of the single nontrivial phase, allowed in the corresponding light neutrino mass matrix $m_ν$, gets fixed and additional constraints ensue from the requirement of matching $η$ with its observed value. Special attention is paid to flavor effects in the washout of the lepton asymmetry. We also comment on the role of small departures from high scale $μτ$ symmetry due to RG evolution.

hep-ph↗
arXiv2010

The magic of four zero neutrino Yukawa textures

Four is the maximum number of texture zeros allowed in the Yukawa coupling matrix of three massive neutrinos. These completely fix the high scale CP violation needed for leptogenesis in terms of that accessible at laboratory energies. $μτ$ symmetry drastically reduces such allowed textures. Only one form of the light neutrinos mass matrix survives comfortably while another is marginally allowed.

hep-ph↗
arXiv2009

'Mu-Tau' symmetry, tribimaximal mixing and four zero neutrino Yukawa textures

Within the type-I seesaw framework with three heavy right chiral neutrinos and in the basis where the latter and the charged leptons are mass diagonal, a near `mu-tau' symmetry in the neutrino sector is strongly suggested by the neutrino oscillation data. There is further evidence for a close to the tribimaximal mixing pattern which subsumes `mu-tau' symmetry. On the other hand, the assumption of a (maximally allowed) four zero texture in the Yukawa coupling matrix Y_nu in the same basis leads to a highly constrained and predictive theoretical scheme. We show that the requirement of an exact `mu-tau' symmetry, coupled with observational constraints, reduces the `seventy two' allowed textures in such a `Y_nu' to 'only four' corresponding to just two different forms of the light neutrino mass matrix `m_nu'. The effect of each of these on measurable quantities can be described, apart from an overall factor of the neutrino mass scale, in terms of two real parameters and a phase angle all of which are within very constrained ranges. The additional input of a tribimaximal mixing reduces these three parameters to `only one' with a very nearly fixed value. Implications for both flavored and unflavored leptogenesis as well as radiative lepton flavor violating decays are discussed. We also investigate the stability of these conclusions under small deviations due to renormalization group running from a high scale where the four zero texture as well as `mu-tau' symmetry or the tribimaximal mixing pattern are imposed.

hep-ph↗
arXiv2009

Developments in high energy theory

This non-technical review article is aimed at readers with some physics background, including beginning research students. It provides a panoramic view of the main theoretical developments in high energy physics since its inception more than half a century ago, a period in which experiments have spanned an enormous range of energies, theories have been developed leading up to the Standard Model, and proposals -- including the radical paradigm of String Theory -- have been made to go beyond the Standard Model. The list of references provided here is not intended to properly credit all original work but rather to supply the reader with a few pointers to the literature, specifically highlighting work done by Indian authors.

physics.pop-ph↗
arXiv2009

Phenomenological consequences of four zero neutrino Yukawa textures

For type I seesaw and in the basis where the charged lepton and heavy right-handed neutrino mass matrices are real and diagonal, four has been shown to be the maximum number of zeros allowed in the neutrino Yukawa coupling matrix $Y_ν$. These four zero textures have been classified into two distinct categories. We investigate certain phenomenological consequences of these textures within a supersymmetric framework. This is done by using conditions implied on elements of the neutrino Majorana mass matrix for textures of each category in $Y_ν$. These conditions turn out to be stable under radiative corrections. Including the effective mass, which appears in neutrinoless double beta decay, along with the usual neutrino masses, mixing angles and phases, it is shown analytically and through scatter plots how restricted regions in the seesaw parameter space are selected by these conditions. We also make consequential statements on the yet unobserved radiative lepton flavor violating decays such as $μ\to e γ$. All these decay amplitudes are proportional to the moduli of entries of the neutrino Majorana mass matrix. We also show under which conditions the low energy CP violation, showing up in neutrino oscillations, is directly linked to the CP violation required for producing successful flavor dependent and flavor independent lepton asymmetries during leptogenesis.

hep-ph↗
arXiv2008

Dirac Leptogenesis in extended nMSSM

We show that a version of the nearly Minimal Supersymmetric Standard Model (nMSSM), extended only in the singlet sector to include the additional superfields of right-handed neutrinos and very heavy Dirac particles conserving $B-L$, admits a viable scenario for Dirac leptogenesis and naturally small Dirac neutrino masses. The origin of the ($B-L$)-conserving high singlet neutrino scale and the desired supersymmetry breaking terms is associated with dynamical supersymmetry breaking in the hidden sector.

hep-ph↗
arXiv2008

Four Zero Neutrino Yukawa Textures in the Minimal Seesaw Framework

We investigate, within the Type I seesaw framework, the physical implications of zero textures in the Yukawa couplings which generate the neutrino Dirac mass matrix $m_D$. It is shown that four is the maximal number of texture zeroes compatible with the observed leptonic mixing and the assumption that no neutrino mass vanishes. We classify all allowed four-zero textures of $m_D$ into two categories with three classes each. We show that the different classes, in general, admit CP violation both at low and high energies. We further present the constraints obtained for low energy physics in each case. The r\^ ole of these zero textures in establishing a connection between leptogenesis and low energy data is analysed in detail. It is shown that it is possible in all cases to completely specify the parameters relevant for leptogenesis in terms of light neutrino masses and leptonic mixing together with the unknown heavy neutrino masses.

hep-ph↗
arXiv2007

Radiatively broken symmetries of nonhierarchical neutrinos

Symmetry-based ideas, such as the quark-lepton complementarity (QLC) principle and the tri-bimaximal mixing (TBM) scheme, have been proposed to explain the observed mixing pattern of neutrinos. We argue that such symmetry relations need to be imposed at a high scale $Λ\sim 10^{12}$ GeV characterizing the large masses of right-handed neutrinos required to implement the seesaw mechanism. For nonhierarchical neutrinos, renormalisation group evolution down to a laboratory energy scale $λ\sim 10^3$ GeV tends to radiatively break these symmetries at a significant level and spoil the mixing pattern predicted by them. However, for Majorana neutrinos, suitable constraints on the extra phases $α_{2,3}$ enable the retention of those high scale mixing patterns at laboratory energies. We examine this issue within the Minimal Supersymmetric Standard Model (MSSM) and demonstrate the fact posited above for two versions of QLC and two versions of TBM. The appropriate constraints are worked out for all these four cases. Specifically, a preference for $α_2 \approx π$ (i.e. $m_1 \approx -m_2$) emerges in each case. We also show how a future accurate measurement of $θ_{13}$ may enable some discrimination among these four cases in spite of renormalization group evolution.

hep-ph↗
arXiv2007

Neutrino symmetries from high to low scales

Proposed symmetry relations, e.g., quark-lepton complementarity (QLC) or tribimaximal mixing (TBM), need to be imposed at a high scale $\wedge \sim 10^{12}$ GeV characterising the large masses of right-handed neutrinos required to implement the seesaw mechanism. RG evolution down to the laboratory scale $λ\sim 10^3$ GeV, generically prone to spoil these relations and their predicted neutrino mixing patterns, can be made to preserve them by appropriately constraining the Majorana phases $α_{2,3}$. This is explicitly demonstrated in the MSSM for two versions of QLC and two versions of TBM. A preference for $α_2 \simeq π$ (i.e. $m_1 \simeq - m_2$) emerges in each case. Discrimination among the four cases is shown to be possible by future measurements of $θ_{13}$.

hep-ph↗
arXiv2006

Quark-lepton complementarity with quasidegenerate Majorana neutrinos

A basis independent formulation of quark-lepton complementarity is implemented at a high scale for quasidegenerate Majorana neutrinos. It is shown that even with the renormalization group evolution in the minimal supersymmetric standard model, the scenario can be consistent with the data provided a nontrivial role is played by the Majorana phases. Correlated constraints are found on these phases and the neutrino mass scale using the current data. We also indicate how future accurate measurements of the mixing angles can serve as tests of this scenario and restrict the values of the Majorana phases.

hep-ph↗
arXiv2006

Bilarge neutrino mixing from supersymmetry with high-scale nonrenormalizable interactions

We suggest a supersymmetric (SUSY) explanation of neutrino masses and mixing, where nonrenormalizable interactions in the hidden sector generate lepton number violating Majorana mass terms for both right-chiral sneutrinos and neutrinos. It is found necessary to start with a superpotential including an array of gauge singlet chiral superfields. This leads to nondiagonal $ΔL = 2$ mass terms and almost diagonal SUSY breaking $A$-terms. As a result, the observed pattern of bilarge mixing can be naturally explained by the simultaneous existence of the seesaw mechanism and radiatively induced masses. Allowed ranges of parameters in the gauge singlet sector are delineated, corresponding to each of the cases of normal hierarchy, inverted hierarchy and degenerate neutrinos.

hep-ph↗
arXiv2006

Probing the deviation from maximal mixing of atmospheric neutrinos

Pioneering atmospheric muon neutrino experiments have demonstrated the near-maximal magnitude of the flavor mixing angle $θ_{23}$. But the precise value of the deviation $D \equiv 1/2 - \sin^2 θ_{23}$ from maximality (if nonzero) needs to be known, being of great interest -- especially to builders of neutrino mass and mixing models. We quantitatively investigate in a three generation framework the feasibility of determining $D$ in a statistically significant manner from studies of the atmospheric $ν_μ,\barν_μ$ survival probability including both vacuum oscillations and matter effects. We show how this determination will be sharpened by considering the up-down ratios of observed $ν_μ$- and $\barν_μ$-induced events and the differences of these ratios in specified energy and zenith angle bins. We consider 1 Megaton year of exposure to a magnetized iron calorimeter such as the proposed INO detector ICAL, taking into account both energy and zenith angle resolution functions. The sensitivity of such an exposure and the dependence of the determination of $D$ on the concerned oscillation parameters are discussed in detail. The vital use of matter effects in fixing the octant of $θ_{23}$ is highlighted.

hep-ph↗
arXiv2006

Event shape discrimination of supersymmetry from large extra dimensions at a linear collider

The production of a charged lepton (e/mu) pair with a large missing energy at a linear collider is discussed as a means of distinguishing the minimal supersymmetry (MSSM) scenario from that with large extra dimensions (ADD) for parameter ranges where the total cross sections are comparable for both. Analyses in terms of event shape variables, specifically sphericity and thrust, are shown to enable a clear discrimination in this regard.

hep-ph↗
arXiv2005

Infrared fixed point of the top Yukawa coupling in split supersymmetry

The severe constraints imposed on the parameter space of the minimal split supersymmetry model by the infrared fixed point solution of the top Yukawa coupling $Y_t$ are studied in detail in terms of the value of the top quark mass measured at the Tevatron together with the lower bound on the lightest Higgs mass established by LEP. The sensitive dependence of the higgsino mass parameter $μ$ and of the gaugino coupling strengths ${\tilde g}_{u,d}$, ${\tilde g}^\prime_{u,d}$ on the value of $Y_t$ in the vicinity of the Landau pole is a remarkable consequence. A few other interesting features emerge, though the model is found to be disfavored within the infrared fixed point scenario because of the need to have several fine tunings at work on account of the requirement of a low upper bound on $\tanβ$.

hep-ph↗
arXiv2004

Higher dimensional models of light Majorana neutrinos confronted by data

We discuss experimental and observational constraints on certain models of higher dimensional light Majorana neutrinos. Models with flavor blind brane-bulk couplings plus three or four flavor diagonal light Majorana neutrinos on the brane, with subsequent mixing induced solely by the Kaluza-Klein tower of states, are found to be excluded by data on the oscillations of solar, atmospheric and reactor neutrinos, taken together with the WMAP upper bound on the sum of neutrino masses. Extra dimensions, if relevant to neutrino mixing, need to discriminate between neutrino flavors.

hep-ph↗