arXiv subjects

Anjan S. Joshipura

Publications and source records attributed to Anjan S. Joshipura.

At least 37 records · Page 2Linked to original sources

arXiv2012

Proceedings of the first workshop on Flavor Symmetries and consequences in Accelerators and Cosmology (FLASY2011)

The main goals of the first "Workshop on FLAvor SYmmetries and consequences in accelerators and cosmology" (FLASY) was to summarize the theoretical status of flavor symmetries, bringing together young researchers in the field to stimulate discussions and new collaborations, with the aim of investigating possible new physics scenarios to be tested at the LHC, as well as in future neutrino, cosmology experiments and dark matter searches.

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arXiv2011

Viability of the exact tri-bimaximal mixing at M_{GUT} in SO(10)

General structures of the charged lepton and the neutrino mixing matrices leading to tri-bimaximal leptonic mixing are determined. These are then integrated into an SO(10) model within which detailed fits to fermion masses and mixing angles are given. It is shown that one can obtain excellent fits to all the fermion masses and quark mixing angles keeping tri-bimaximal leptonic mixing intact. Different perturbations to the basic structure are considered and those which can or which cannot account for the recent T2K and MINOS results on the reactor mixing angle $θ_{13}^l$ are identified.

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arXiv2011

Fermion Masses in SO(10) Models

We examine many SO(10) models for their viability or otherwise in explaining all the fermion masses and mixing angles. This study is carried out for both supersymmetric and non-supersymmetric models and with minimal ($10+\bar{126}$) and non-minimal ($10+\bar{126}+120$) Higgs content. Extensive numerical fits to fermion masses and mixing are carried out in each case assuming dominance of type-II or type-I seesaw mechanism. Required scale of the B-L breaking is identified in each case. In supersymmetric case, several sets of data at the GUT scale with or without inclusion of finite supersymmetric corrections are used. All models studied provide quite good fits if the type-I seesaw mechanism dominates while many fail if the type-II seesaw dominates. This can be traced to the absence of the $b$-$τ$ unification at the GUT scale in these models. The minimal non-supersymmetric model with type-I seesaw dominance gives excellent fits. In the presence of a $45_H$ and an intermediate scale, the model can also account for the gauge coupling unification making it potentially interesting model for the complete unification. Structure of the Yukawa coupling matrices obtained numerically in this specific case is shown to follow from a very simple U(1) symmetry and a Froggatt-Nielsen singlet.

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arXiv2010

Implications of CP violating 2HDM in B physics

The charged fermion mass matrices are invariant under $U(1)^3$ symmetry linked to the fermion number transformation. Under the condition that the definition of this symmetry in arbitrary weak basis does not depend upon Higgs parameters such as ratio of vacuum expectation values, a class of two Higgs doublet models (2HDM) can be identified in which tree level flavor changing neutral currents normally present in 2HDM are absent. However unlike the type I or type II Higgs doublet models, the charged Higgs couplings in these models contain additional flavor dependent CP violating phases. These phases can account for the recent hints of the beyond standard model CP violation in the $B_d$ and $B_s$ mixing. In particular, there is a range of parameters in which new phases do not contribute to the $K$ meson CP violation but give identical new physics phases in the $B_d$ and $B_s$ meson mixing.

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arXiv2010

Quasi-degenerate neutrinos in SO(10)

Quark lepton universality inherent in grand unified theories based on $SO(10)$ gauge group generically leads to hierarchical neutrino masses. We propose a specific ansatz for the structure of Yukawa matrices in $SO(10)$ models which differ from this generic expectations and lead to quasi degenerate neutrinos through the type-I seesaw mechanism. Consistency of this ansatz is demonstrated through a detailed fits to fermion masses and mixing angles all of which can be explained with reasonable accuracy in a model which uses the Higgs fields transforming as $10,120$ and $\overline{126}$ representations of $SO(10)$. The proposed ansatz is shown to follow from an extended model based on the three generations of the vector like fermions and an $O(3)$ flavour symmetry. Successful numerical fits are also discussed in earlier proposed models which used combination of the type-I and type-II seesaw mechanisms for obtaining quasi degenerate neutrinos. Large neutrino mixing angles emerge as a consequence of neutrino mass degeneracy in both these cases.

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arXiv2010

Fermion number conservation and two Higgs doublet models without tree level flavour changing neutral currents

The charged fermion mass matrices are always invariant under $U(1)^3$ symmetry linked to the fermion number transformation. A class of two Higgs doublet models (2HDM) can be identified by requiring that the definition of this symmetry in an arbitrary weak basis be independent of Higgs parameters such as the ratio of the Higgs vacuum expectation values. The tree level flavour changing neutral currents normally present in 2HDM are absent in this class of models but unlike the type I or type II Higgs doublet models, the charged Higgs couplings in these models contain additional flavour dependent CP violating phases. These phases can account for the recent hints of the beyond standard model CP violation in the $B_d$ and $B_s$ mixing. In particular, there is a range of parameters in which new phases do not contribute to the $K$ meson CP violation but give identical new physics contribution to the $B_d$ and $B_s$ meson mixing. Specific model realizations of the above scenario are briefly discussed.

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arXiv2009

Type I seesaw mechanism for quasi degenerate neutrinos

We discuss symmetries and scenarios leading to quasi-degenerate neutrinos in type-I seesaw models. The existence of degeneracy in the present approach is not linked to any specific structure for the Dirac neutrino Yukawa coupling matrix $y_D$ and holds in general. Basic input is the application of the minimal flavour violation principle to the leptonic sector. Generalizing this principle, we assume that the structure of the right handed neutrino mass matrix is determined by $y_D$ and the charged lepton Yukawa coupling matrix $y_l$ in an effective theory invariant under specific groups ${\cal G}_F$ contained in the full symmetry group of the kinetic energy terms. ${\cal G}_F$ invariance also leads to specific structure for the departure from degeneracy. The neutrino mass matrix (with degenerate mass $m_0$) resulting after seesaw mechanism has a simple form ${\cal M}_ν\approx m_0(I-p y_ly_l^T)$ in one particular scenario based on supersymmetry. This form is shown to lead to correct description of neutrino masses and mixing angles. The thermal leptogenesis after inclusion of flavour effects can account for the observed baryon asymmetry of the universe within the present scenario. Rates for lepton flavour violating processes can occur at observable levels in the supersymmetric version of the scenario.

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arXiv2009

Maximal mixing as a `sum' of small mixings

In models with two sources of neutrino masses, we look at the possibility of generating maximal/large mixing angles in the total mass matrix, where both the sources have only small mixing angles. We show that in the two generation case, maximal mixing can naturally arise only when the total neutrino mass matrix has a quasi-degenerate pattern. The best way to demonstrate this is by decomposing the quasi-degenerate spectrum in to hierarchial and inverse-hierarchial mass matrices, both with small mixing. Such a decomposition of the quasi-degenerate spectra is in fact very general and can be done irrespective of the mixing present in the mass matrices. With three generations, and two sources, we show that only one or all the three small mixing angles in the total neutrino mass matrix can be converted to maximal/large mixing angles. The decomposition of the degenerate pattern in this case is best realised in to sub-matrices whose dominant eigenvalues have an alternating pattern. On the other hand, it is possible to generate two large and one small mixing angle if either one or both of the sub-matrices contain maximal mixing. We present example textures of this. With three sources of neutrino masses, the results remain almost the same as long as all the sub-matrices contribute equally. The Left-Right Symmetric model where Type I and Type II seesaw mechanisms are related provides a framework where small mixings can be converted to large mixing angles, for degenerate neutrinos.

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arXiv2009

Higgs induced FCNC as a source of new physics in $b\to s $ transitions

The observations in the $B_{s}$ sector suggest the existence of some new physics contribution to the $B_S-\bar{B}_s$ mixing. We study the implications of a hypothesis that this contribution is generated by the Higgs induced flavour changing neutral currents. We concentrate on the specific $b\to s$ transition which is described by two complex FCNC parameters $F_{23}$ and $F_{32}$ and parameters in the Higgs sector. Model independent constraints on these parameters are derived from the $B_S-\bar{B}_s$ mixing and are used to predict the branching ratios for $\bar{B}_s\to μ^+μ^-$ and $\bar{B}_d\to \bar{K}μ^+μ^-$ numerically by considering general variations in the Higgs parameters assuming that Higgs sector conserves CP. Taking the results on $B_{s}^0-\bar{B}_{s}^0$ mixing derived by the global analysis of UTfit group as a guide we present the general constraints on $F_{23}^*F_{32}$ in terms of the pseudo-scalar mass $M_A$. The former is required to be in the range $\sim (1-5) \times 10^{-11} M_A^2 {\rm GeV}^{-2}$ if the Higgs induced FCNC represent the dominant source of new physics. The phases of these couplings can account for the large CP violating phase in the $B_{s}^0-\bar{B}_{s}^0$ mixing except when $F_{23}=F_{32}$. The Higgs contribution to $\bar{B}_s\to μ^+μ^-$ branching ratio can be large, close to the present limit while it remains close to the standard model value in case of the process $\bar{B}_d\to \bar{K}μ^+μ^-$ for all the models under study. We identify and discuss various specific examples which can naturally lead to suppressed FCNC in the $K^0-\bar{K}^0$ mixing allowing at the same time the required values for $F_{23}^*$ and $F_{32}$.

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arXiv2009

Scaling in the Neutrino Mass Matrix, mu-tau Symmetry and the See-Saw Mechanism

The scaling hypothesis postulates proportionality of two columns of the Majorana neutrino mass matrix in the flavor basis. This Ansatz was shown to lead to an inverted hierarchy and U_{e3} = 0. We discuss theoretical and phenomenological properties of this hypothesis. We show that (i) the neutrino mass matrix with scaling follows as a consequence of a generalized mu-tau symmetry imposed on the type-I see-saw model; (ii) there exists a unique texture for the Dirac mass matrix m_D which leads to scaling for arbitrary Majorana matrix M_R in the context of the type-I see-saw mechanism; (iii) unlike in the mu-tau symmetric case, a simple model with two right-handed neutrinos and scaling can lead to successful leptogenesis both with and without the inclusion of flavor effects.

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arXiv2009

Fermion Masses and Mixings in a $μ$-$τ$ symmetric SO(10)

$μ$-$τ$ symmetry imposed on the neutrino mass matrix in the flavour basis is known to be quite predictive. We integrate this very specific neutrino symmetry into a more general framework based on the supersymmetric SO(10) grand unified theory. As in several other models, the fermion mass spectrum is determined by Hermitian mass matrices resulting from the renormalizable Yukawa couplings of the 16-plet of fermions with the Higgs fields transforming as $10, \bar{126},120$ representations of the SO(10) group. The $μ$-$τ$ symmetry is spontaneously broken through the 120-plet. Consequences of this scheme are considered for fermion masses using both type-I and type-II seesaw mechanism. This scenario is shown to lead to a generalized CP invariance of the mass matrices and vanishing CP violating phases if the Yukawa couplings are invariant under the $μ$-$τ$ symmetry. Small explicit breaking of the $μ$-$τ$ symmetry is then shown to provide a very good understanding of all the fermion masses and mixing. Detailed fits to the fermion spectrum are presented in several scenarios. One obtains a very good fit to all observables in the context of the type-I seesaw mechanism but type-II seesaw model also provides a good description except for the overall scale of the neutrino masses. Three major predictions on the leptonic mixing parameters in the type-I seesaw case are (1) the atmospheric mixing angle $θ_{23}^{l}$ close to maximal, (2) $θ_{13}^{l}$ close to the present upper bound and (3) negative but very small Dirac CP violating phase in the neutrino oscillations.

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arXiv2007

Minimal flavour violations and tree level FCNC

Consequences of a specific class of two Higgs doublet models in which the Higgs induced tree level flavour changing neutral currents (FCNC) display minimal flavour violation (MFV) are considered. These FCNC are fixed in terms of the CKM matrix elements and the down quark masses. The minimal model in this category with only two Higgs doublets has no extra CP violating phases but such a phase can be induced by adding a complex singlet. Many of the theoretical predictions are similar to other MFV scenario. The FCNC contribute significantly to $B$ meson mixing and CP violation. Detailed numerical analysis to determine the allowed Higgs contributions to neutral meson mixings and the CKM parameters $\barρ,\barη$ in their presence is presented. The Higgs induced phase in the $B^0_{d,s}-\bar{B}^0_{d,s}$ transition amplitude $M_{12}^{d,s}$ is predicted to be equal for the $B_d$ and the $B_s$ systems. There is a strong correlation between phases in $M_{12}^{d,s}$ and $|V_{ub}|$. A measurable CP violating phase $ϕ_s=-0.18\pm 0.08$ is predicted on the basis of the observed phase $ϕ_d$ in the $B_d$ system if $|V_{ub}|$ is large and close to its value determined from the inclusive b decays.

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arXiv2007

Complex CKM matrix, spontaneous CP violation and generalized $μ$-$τ$ symmetry

The multi-Higgs models having spontaneous CP violation (SPCV) and natural flavor conservation (NFC) lead to a real CKM matrix $V$ contradicting current evidence in favour of a complex $V$. This contradiction can be removed by using a generalized $μ$-$τ$ (called 23) symmetry in place of the discrete symmetry conventionally used to obtain NFC. If 23 symmetry is exact then the Higgs induced flavour changing neutral currents (FCNC) vanish as in case of NFC. 23 breaking introduces SPCV, a phase in $V$ and suppressed FCNC among quarks. The FCNC couplings $F_{ij}^{d,u}$ between $i$ and $j$ generations show a hierarchy $|F_{12}^{d,u}|<|F_{13}^{d,u}|<|F_{23}^{d,u}|$ with the result that the FCNC can have observable consequences in $B$ mixing without conflicting with the $K^0-\bar{K}^0$ mixing. Detailed fits to the quark masses and the CKM matrix are used to obtain the (complex) couplings $F_{ij}^d$ and $F_{ij}^u$. Combined constraints from flavour and CP violations in the $K,B_d,B_s,D$ mesons are analyzed within the model. They allow ($i$) relatively light Higgs, 100-150 GeV ($ii$) measurable extra contributions to the magnitudes and phases of the $B^0_{d,s}-\bar{B}^0_{d,s}$ mixing amplitudes and ($iii$) the $D^0-\bar{D}^0$ mixing at the current sensitivity level.

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arXiv2007

Predictive flavour symmetries of the neutrino mass matrix

Here we propose an $A_4$ flavour symmetry model which implies a lower bound on the neutrinoless double beta decay rate, corresponding to an effective mass parameter $M_{ee} \gsim 0.03$ eV, and a direct correlation between the expected magnitude of CP violation in neutrino oscillations and the value of $\sin^2θ_{13}$, as well as a nearly maximal CP phase $δ$.

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arXiv2006

Constraints on flavor-dependent long range forces from neutrino experiments

We study the impact of flavor-dependent long range leptonic forces mediated by the $L_e-L_μ$ or $L_e -L_τ$ gauge bosons on the solar neutrino oscillations, when the interaction range $R_{LR}$ is much larger than the Earth-Sun distance. The solar and atmospheric neutrino mass scales do not get trivially decoupled in this situation even if $θ_{13}$ is vanishingly small. In addition, for $α\gsim 10^{-52}$ and normal hierarchy, resonant enhancement of $θ_{13}$ may give rise to strong energy dependent effects on the $ν_e$ survival probability. A complete three generation analysis of the solar neutrino and KamLAND data gives the $3σ$ limits $α_{eμ} < 3.4 \times 10^{-53}$ and $α_{eτ} < 2.5 \times 10^{-53}$ when $R_{LR}$ is much smaller than our distance from the galactic center. With larger $R_{LR}$, the collective LR potential due to all the electrons in the galaxy becomes significant and the constraints on $α$ become stronger by upto two orders of magnitude.

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arXiv2006

Constraints on flavor-dependent long range forces from solar neutrinos and KamLAND

Flavor-dependent long range (LR) leptonic forces, like those mediated by the $L_e-L_μ$ or $L_e -L_τ$ gauge bosons, constitute a minimal extension of the standard model that preserves its renormalizability. We study the impact of such interactions on the solar neutrino oscillations when the interaction range $R_{LR}$ is much larger than the Earth-Sun distance. The LR potential can dominate over the standard charged current potential inside the Sun in spite of strong constraints on the coupling $α$ of the LR force coming from the atmospheric neutrino data and laboratory search for new forces. We demonstrate that the solar and atmospheric neutrino mass scales do not get trivially decoupled even if $θ_{13}$ is vanishingly small. In addition, for $α\gsim 10^{-52}$ and normal hierarchy, resonant enhancement of $θ_{13}$ results in nontrivial energy dependent effects on the $ν_e$ survival probability. We perform a complete three generation analysis, and obtain constraints on $α$ through a global fit to the solar neutrino and KamLAND data. We get the $3σ$ limits $α_{eμ} < 3.4 \times 10^{-53}$ and $α_{eτ} < 2.5 \times 10^{-53}$ when $R_{LR}$ is much smaller than our distance from the galactic center. With larger $R_{LR}$, the collective LR potential due to all the electrons in the galaxy becomes significant and the constraints on $α$ become stronger by upto two orders of magnitude.

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arXiv2005

Quark-Lepton universality and large leptonic mixing

A unified description of fermionic mixing is proposed which assumes that in certain basis ($i$) a single complex unitary matrix $V$ diagonalizes mass matrices of all fermions to the leading order, ($ii$) the SU(5) relation $M_d=M_l^T$ exists between the mass matrices of the down quarks and the charged leptons, and ($iii$) $M_d^\dagger=M_d$. These assumptions automatically lead to different mixing patterns for quarks and leptons: quarks remain unmixed to leading order ($i. e. V_{CKM}=1$) while leptons have non-trivial mixing given by a symmetric unitary matrix $V^0_{PMNS} = V^T V$. $V$ depends on two physical mixing angles and for values of these angles $\sim 20^\circ-25 ^\circ$ it reproduces the observed mixing patterns rather well. We identify conditions under which the universal mixing $V$ follows from the universal mass matrices of fermions. Relatively small perturbations to the leading order structure lead to the CKM mixing and corrections to $V^0_{PMNS}$. We find that if the correction matrix equals the CKM matrix, the resulting lepton mixing agrees well with data and predicts $\sin θ_{13} > 0.08$. In a more general context, the assumption of partial universality ($i.e.$, different mixing for the up and the down components of doublets) is shown to lead to a complementarity relation $V_{PMNS}V_{CKM}=V^TV$ in the lowest order.

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arXiv2005

Universal 2-3 symmetry

Possible maximal mixing seen in the oscillations of the atmospheric neutrinos has led to postulate of a $μ$-$τ$ symmetry which interchanges $ν_μ$ and $ν_τ$. We argue that such symmetry need not be special to neutrinos but can be extended to all fermions. The assumption that all fermion mass matrices are approximately invariant under interchange of the second and the third generation fields is shown to be phenomenologically viable and has interesting consequences. In the quark sector, the smallness of $V_{ub}$ and $V_{cb}$ can be a consequences of this approximate 2-3 symmetry. The same approximate symmetry can simultaneously lead to large atmospheric mixing angle and can describe the leptonic mixing quite well provided the neutrino spectrum is quasi degenerate. We present this scenario, elaborate on its consequences and discuss its realization.

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