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Biswajoy Brahmachari

Publications and source records attributed to Biswajoy Brahmachari.

At least 37 records · Page 2Linked to original sources
arXiv2002

A minimal three generation seesaw scenario for LSND

We show that in the minimal three generation seesaw models for neutrinos, the presence of leptonic $(L_e+L_μ-L_τ)\times S_2$ symmetry leads to one of the right handed neutrinos remaining massless. This state can then be identified with the sterile neutrino required for a simultaneous understanding of solar, atmospheric and LSND observations. We present a gauge model where the presence of higher dimensional operators originating from Planck scale physics lead to a realistic 2+2 mixed scenario that fits all oscillation data. The model predicts a range for the mixing angle $U_{e3}$ and an effective mass for neutrinos emitted in tritium decay, which can be used to test this model.

hep-ph↗
arXiv2002

Neutrinoless Double Beta Decay with Negligible Neutrino Mass

If the electron neutrino has an effective nonzero Majorana mass, then neutrinoless double beta decay will occur. However, the latter is possible also with a negligible neutrino mass. We show how this may happen in a simple model of scalar diquarks and dileptons. This possibility allows neutrino masses to be small and hierarchical, without conflicting with the possible experimental evidence of neutrinoless double beta decay.

hep-ph↗
arXiv2002

Viability of bi-maximal solution of the Zee mass matrix

We know $L_e-L_μ-L_τ$ symmetry gives $m^2_1= m^2_2 >> m^2_3$ pattern in Zee model. $Δm^2_\odot$ emerges from a small breaking of this symmetry. Because this symmetry is broken very weakly $θ_\odot$ does not deviate much from $\tan^2 θ_\odot=1$ which is its value in the symmetric limit. This gives a mismatch with LMA solution where mixing is large but not exactly maximal. We confront this property of Zee mass matrix by phenomenologically analyzing recent results from solar and atmospheric neutrino oscillation experiments at various confidence levels. We conclude that LOW type solution is compatible with the Zee mass matrix at 99% confidence level when atmospheric neutrino deficit is explained by maximal $ν_μ\leftrightarrow ν_τ$ oscillation. Thus the minimal version of the Zee model even though disfavored by the LMA type or VO type solutions, is compatible with LOW type solution of solar neutrino problem.

hep-ph↗
arXiv2002

Adjoint bulk scalars and supersymmetric unification in the presence of extra dimensions

There are several advantages of introducing adjoint superfields at intermediate energies around $M=10^{13}$ GeV. Such as (i) gauge couplings still unify (ii) neutrino masses and mixings are produced (iii) primordial lepton asymmetry can be produced. We point out that if adjoint scalars have bulk excitations along with gauge bosons whereas fermions and the doublet scalar live on boundary then N=2 supersymmetric beta functions $\tilde{b_i}$ vanish. Thus even if extra dimensions open up at an intermediate scale $μ_0$ and all N=2 Yang-Mills fields as well as N=2 matter fields in the adjoint representation propagate in the bulk, still gauge couplings renormalize beyond $μ_0$ just like they do in 4-dimensions with adjoint scalars. Consequently unification is achieved in the presence to extra dimensions, mass scales are determined uniquely via Renormalization Group Equations(RGE) and unification scale remains high enough to suppress proton decay. This scenario can be falsified if we get signatures of extra dimensions at low energy.

hep-ph↗
arXiv2001

Supersymmetric Model of Neutrino Mass and Leptogenesis with String-Scale Unification

Adjoint supermultiplets (1,3,0) and (8,1,0) modify the evolution of gauge couplings. If the unification of gauge couplings occurs at the string scale, their masses are fixed at around $10^{13}$ GeV. This scale coincides with expected gaugino condensation scale in the hidden sector $M_{string}^{2/3} m^{1/3}_{3/2} \sim 10^{13}$ GeV. We show how neutrino masses arise in this unified model which naturally explain the present atmospheric and solar neutrino data. The out-of-equilibrium decay of the superfield (1,3,0) at $10^{13}$ GeV may also lead to a lepton asymmetry which then gets converted into the present observed baryon asymmetry of the Universe.

hep-ph↗
arXiv2000

An apprach to generate large and small leptonic mixing angles

We take up the point of view that Yukawa couplings can be either 0 or 1, and the mass patterns of fermions are generated purely from the structure of the Yukawa matrices. We utilize such neutrino as well as charged leptonic textures which lead to (maximal) mixing angles of $π/4$ in each sector for relevant transitions. The combined leptonic CKM mixing angles are $π/4 \pm π/4$ which lead to very small $\sin^2 2 Θ$ relevant to solar neutrino and LSND experiments. We propose that on the other hand the absence of the charged leptonic partner of the sterile neutrino maintains the angle $π/4$ from the neutrino sector for the transition $ν_μ\leftrightarrow ν_s$ and hence atmospheric neutrino anomaly is explained through maximal mixing.

hep-ph↗
arXiv2000

Lattice simulations of the strange quark mass and Fritzsch texture

A number of numerical simulations of lattice gauge theory have indicated a low mass of strange quark in 100 MeV range at the scale of $μ=2$ GeV. In the unquenched case, which is improved over the simulation in the quenched approximation by the inclusion of $u$ and $d$ sea quark effects, one sees a further downward trend. Here the fermion mass spectrum of the Fritzsch texture is recalculated. In a single step supersymmetric GUT with $M_X \sim 10^{16}$ GeV such values of the strange quark mass can be obtained for low values of $\tan β$. Experimental numbers $m^{pole}_t = 173 \pm 6$ GeV and $4.1 < m_b(m_b) < 4.4$ GeV are used in this study. Since the scenario is supersymmetric, gaugino loop diagrams contribute to the masses in addition to usual tree level Yukawa contributions. Upper bound of the mixing parameter $V_{cb}$ is taken at 0.045

hep-ph↗
arXiv1999

Semi-perturbative unification with extra vector-like families

We make a comprehensive analysis of an extended supersymmetric model(ESSM) obtained by adding a pair of vector-like families to the minimal supersymmetric standard model and having specific forms of 5 x 5 fermion mass matrices. The singlet Higgs couplings which link the ordinary to vector-like generations do not have the renormalization effects of the gauge interactions and hence the "quasi-infrared fixed point" near the scale of the top quark mass. The two-loop Yukawa effects on gauge couplings lead to an unified coupling $α_X$ around 0.2 with an unification scale M_X of 10^{16.9} GeV. Large Yukawa effects in the high energy region arrest the growth of the QCD coupling near M_X making the evolution flat. The renormalization effects of the vector-like generations on soft mass parameters has important effects on the charge and color breaking(CCB)minima. We will show that there exists parameter space where there is no charge and color breaking. We will also demonstrate that there exists minima of the Higgs potential which satisfies the mass of the Z boson but avoid CCB. Upper limits on the mass of the lightest Higgs boson from the one-loop effective scalar potential is obtained for sets of universal soft supersymmetry breaking mass parameters.

hep-ph↗
arXiv1999

Leptogenesis and Yukawa textures

We study a set of textures giving rise to correct masses and mixings of the charged fermions in the context of leptogenesis. The Dirac neutrino texture pattern is assumed to be identical with the up quark texture. The heavy Majonana neutrino mass matrix is obtained by inverting the type-I see-saw formula and using the neutrino masses and mixings required by the solar and atmospheric neutrino oscillation experiments as input. After making the feasibility study of the generated lepton asymmetry via the decay of the heavy right handed neutrino, we compute the generated baryon asymmetry by numerically solving the supersymmetric Boltzmann equations. We find for these models that both the hierarchy of the texture as well as the placement of the texture zeros are important to the viability of leptogenesis as the source of the observed baryon asymmetry of the universe.

hep-ph↗
arXiv1999

A See-saw model of sterile neutrino

If the smallness of the mass of the sterile neutrino is to be explained by the see-saw mechanism, the off-diagonal entries of the mass matrix needs to be protected by some symmetry not far above the electroweak scale. We implement see-saw mechanism in a gauge model based on $SU(2)^q_L \times SU(2)^l_L \times U(1)^q_Y \times U(1)^l_Y$ un-unified gauge group which breaks to $SU(2)_L \times U(1)_Y$ at the TeV region via a two-step symmetry breaking chain. The right handed diagonal block is tied to the highest scale up to which the un-unification symmetry holds. The sterile neutrino emerges from a quark-lepton mixed representation of the un-unified group.

hep-ph↗
arXiv1998

Effects of 126 dimensional Higgs scalar on Bottom-Tau unification and quasi-infrared fixed point

In the presence of ${\bf 126 + \bar{126}}$ Higgs multiplets in a SO(10) theory, the fermion masses get contributions from an induced vacuum expectation value (VEV) of a $SU(2)_L$ doublet residing in ${\bf 126}$ which differentiates between quarks and leptons by a relative sign leading to a significant correction to the prediction of the mass ratio of the bottom quark and the tau lepton for ranges of the mass of this extra doublet. We perform a two-loop renormalization group analysis of the minimal version of the one-step supersymmetric SO(10) model to display this and re-calculate the corrections to the top quark mass in the presence of such an induced VEV. We show that these effects make the infra-red fixed point scenario consistent with experimental results.

hep-ph↗
arXiv1998

Asymmetric neutrino Yukawa matrices and neutrino mixing

We study leptonic CKM mixing matrices when the neutrino Yukawa matrices are antisymmetric which gives rise to mass patterns suitable to explain solar, atmospheric and LSND neutrino oscillation experiments. Taking diagonal leptonic matrices which can give rise to hierarchical lepton masses, we compute the leptonic CKM matrix.

hep-ph↗
arXiv1998

Grand Unification of the Sterile Neutrino

The simplest way to simultaneously understand all existing indications of neutrino oscillations from solar and atmospheric neutrino deficits and the LSND experiment, seems to be to postulate a sterile neutrino. We present a realistic grand unified model based on the gauge group $SO(10)\times SO(10)^\prime$ that leads to the desired masses and mixings for the sterile and the known neutrinos needed to understand the above observations while fitting those of the known charged fermions. The model is a grand unified realization of the recently proposed idea that the sterile neutrino is the lightest neutrino of a mirror sector of the universe which has identical matter and gauge content as the standard model. The two SO(10)'s operate on the two sectors in a mirror symmetric way and are connected by a mixed Higgs representations whose net effect is to connect the superheavy right handed neutrinos of the two sectors.

hep-ph↗
arXiv1997

Low Energy Grand Unification With SU(16)

We study the possibility of achieving low unification scale in a grand unification scheme based on the gauge group SU(16). Baryon number symmetry being an explicit local gauge symmetry here gauge boson mediated proton decay is absent. We present in detail a number of symmetry breaking patterns and the higgs field representations giving rise to the desired symmetry breakings and identify one chain giving low energy unification. These higgs field representations are constructed in such a way that higgs mediated proton decay is absent. At the end we indicate the very rich low energy physics obtainable from this model which includes quark-lepton un-unified symmetry and chiral color symmetry. In brief some phenomenological implications are also studied.

hep-ph↗
arXiv1997

Recent direct measurement of the Top quark mass and quasi-infrared fixed point

We note that the recent direct measurement of the top quark mass at $173.3 \pm 5.6 (stat) \pm 6.2 (syst)$ by D0 collaboration severely constrains the theoretically attractive infra-red fixed point scenario of the top quark Yukawa coupling in supersymmetric GUTs. For one-step unified models the above mentioned measurement bounds the arbitrary but experimentally determinable parameter $\tan β$ to the range $1.3 \le \tan β\le 2.1$. Further crunch on the top quark mass may determine $\tan β$ even more accurately within the fixed point scenario. On the other hand an experimental value of $\tan β> 2.1$ will rule out the fixed point scenario bounding $h^2_t(M_X)/4 π$ to 0.022 from above.

hep-ph↗
arXiv1996

Light adjoint scalars and unification at the string scale

Following the suggestion of Bachas, Fabre and Yanagida (BFY), we analyze the gauge coupling unification at the two-loop order, in a supersymmetric scenario where scalars belonging to the adjoint representations contribute to the evolution of the couplings from intermediate scales onward, and the unification scale is pushed towards the string scale. Thereafter, we compare the masses of these adjoint scalars to the scale at which the hidden sector gauge coupling reaches the non-perturbative limit at the two-loop order for various possible hidden sector gauge groups motivated by the the conjecture of BFY that the masses of these adjoint scalars are related to gaugino condensation. We also compute the predictions for the top and bottom quark masses in this scenario and compare them with those of MSSM. The predicted bottom mass improves in the BFY scenario for smaller values of $α_s$.

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