PHYS08200604017 Manimala Mitra - Homi Bhabha National Institute

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calculations for lepton flavor violating radiative as well as tree level decays of a generic type-III seesaw model have been published in [28,29]. The authors of these papers have also worked out the current constraints on the deviation from unitarity. Even for 100 GeV mass range heavy leptons, the predicted non-unitarity and lepton flavor violating decay rates should be below the current experimental bounds. 3.4 Heavy Fermion Production at LHC Here we discuss the heavy fermion production at LHC. The triplet fermions couple to the standard model particles through the Yukawa couplings as well as gauge couplings. We give in Appendix B, the detailed Yukawa and gauge couplings of the neutral and charged heavy fermions with the standard model leptons, vector bosons, and Higgs particles. We have kept the masses of the heavy fermions in the 100 GeV to 1 TeV range. Therefore, it should be possible to produce these fermions at LHC. In this section, we will study in depth the production and detection possibilities of the heavy leptons in our type-III seesaw model. Compared to the usual type-III seesaw model, there are two distinctly new aspects in our analysis – (i) presence of two Higgs doublet instead of one, leading to a rich collider phenomenology, (ii) presence of µ-τ symmetry in our model. The heavy triplet fermion production at LHC has been discussed by many earlier papers At LHC we will be looking at the following production channels pp → Σ ± m Σ∓ m ,Σ± m Σ0 m ,Σ0 m Σ0 m . To remind once more, the subscript “m” denote 4 component fields in their mass basis. The exotic fermions have both Yukawa couplings to Higgs as well as gauge couplings to vector bosons. Therefore, they could be in principle produced through either gauge mediated partonic processes (left diagram) or through Higgs mediated partonic processes (right diagram) ¯q m /q ′ m Σ ± m ¯q m /q ′ m Σ ± m Z/γ/W ± h 0 /A 0 H 0 /H ± q m Σ 0 m/ Σ ∓ m q m Σ 0 m / Σ∓ m However, it turns out that the vertex factors for the couplings of heavy fermions to gauge bosons which are relevant for the formers production, viz., Σ + mΣ − mZ/γ and Σ 0 m Σ± m W∓ , are much larger than those involving the Higgs, viz., Σ + m Σ− m H0 /h 0 /A 0 and Σ 0 m Σ± m H∓ . To illustrate this with a specific example, we compare the Σ + m Σ− m Z coupling 48
Figure 3.4: Variation of production cross section of Σ ± m , Σ0 m with the mass of exotic leptons. The blue, red and pink lines correspond to Σ − m Σ0 m , Σ+ m Σ0 m and Σ− m Σ+ m production respectively. given in Eqs. (B16) and (B17) with the Σ + mΣ − mh 0 coupling given in Table 3.13. It is easy to see that the Σ + m Σ− m Z/γ coupling has terms proportional to T† 22T 22 and S † 22S 22 , while the Σ + m Σ− m h0 coupling depends on terms which have an off-diagonal mixing matrix block. Since the off-diagonal mixing matrix blocks are much smaller than the diagonal ones (as discussed before), it is not surprising that the couplings of two exotic fermions to the Higgs particles are much smaller than to the gauge bosons. Hence the heavy exotic fermions will be produced predominantly via the gauge boson mediated processes. We calculate the cross-sections using the Calchep package [30]. InFig. 3.4weshowtheproductioncross-sectionforΣ − m Σ0 m (bolddottedline), Σ+ m Σ0 m (solid line), andΣ + mΣ − m (fine dotted line), at LHC as a function of the corresponding heavy fermion mass. It is straightforward to see that the Σ 0 m Σ0 m Z (and Σ0 m Σ0 m W± ) couplings are absent. A very small Σ 0 m Σ0 m Z is generated through mixing from the ν0 ν 0 Z coupling. However, this is extremely small. Hence, Σ 0 mΣ 0 m production through gauge interactions is heavily suppressed and is not shown in Fig. 3.4. The production cross-sections of the heavy fermions fall sharply with their mass. More precisely, σ(Σ ± mΣ ∓ m) = 112 fb, σ(Σ + m Σ0 m ) = 206 fb and σ(Σ− m Σ0 m ) = 95 fb, for M Σ i ≃ 300 GeV. However, for M Σi ≃ 600 GeV this quickly falls to σ(Σ ± m Σ∓ m ) = 6 fb, σ(Σ+ m Σ0 m ) = 13 fb, and σ(Σ− m Σ0 m ) = 4 49
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Neutrinos and Some Aspects of Physi
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Declaration This thesis is a presen
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Acknowledgments First and foremost,
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iii
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trino masses are bounded within 0.1
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softly broken Z 2 symmetry, the mas
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tribimaximal mixing in the neutrino
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Bibliography [1] Two Higgs doublet
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Contents 1 Introduction 1 1.1 Stand
Page 25: 6.2.2 Charged Lepton Masses and Mix
Page 29 and 30: Chapter 1 Introduction 1.1 Standard
Page 31 and 32: For positive µ 2 and λ, the Higgs
Page 33 and 34: type of Yukawa interaction between
Page 35 and 36: interaction with the Higgs as λ f
Page 37 and 38: where ˆΦ is the MSSM chiral super
Page 39: (2004); A. Ghosal, hep-ph/0304090;
Page 44 and 45: active flavor. In recent years, sev
Page 46 and 47: Figure 2.1: The possible neutrino s
Page 48 and 49: Majorana mass term breaks lepton nu
Page 50 and 51: The kinetic term of the Higgs tripl
Page 52 and 53: ight handed neutrino N R can be exa
Page 54 and 55: alternating group which is not a di
Page 56 and 57: The group contains two one-dimensio
Page 58 and 59: from neutral-current interactions i
Page 60: [31] K. S. Babu and R. N. Mohapatra
Page 64 and 65: of producing the heavy fermion trip
Page 66 and 67: where Σ ± Ri = Σ1 Ri ∓iΣ2 Ri
Page 68 and 69: while U ν diagonalizes m ν and ˜
Page 70 and 71: It is evident that the masses of th
Page 72 and 73: 0.001 0.001 0.0001 0.0001 U e3 1e-0
Page 74 and 75: if we neglect terms proportional to
Page 78 and 79: fb. Therefore, it is obvious that t
Page 80 and 81: Σ − -> e m 1 m h 0 Σ − -> e m
Page 82 and 83: We can also see that for Σ − m 1
Page 84 and 85: the sinα term. However, decay to h
Page 86 and 87: Σ − m 1 ->ν m1 W Σ 0 m 1 ->ν
Page 88 and 89: Γ 2HDM (Σ 0 m → ν m H 0 ) ≃
Page 90 and 91: Decay modes Σ ± m 1 Σ ± m 2 Σ
Page 92 and 93: III seesaw model. Clearly, for our
Page 94 and 95: Sl no Channels Effective cross-sect
Page 96 and 97: • The other dominant decay channe
Page 102 and 103: 3.9 Conclusions The seesaw mechanis
Page 104 and 105: Appendix A: The Scalar Potential an
Page 106 and 107: B: The Interaction Lagrangian B.1:
Page 108 and 109: C H0 ,L 1√ ll 2 (T 11Y † l S 11
Page 110 and 111: c Z,L ll c Z,L lΣ − c Z,L Σ −
Page 112 and 113: Bibliography [1] S. Weinberg, Phys.
Page 114: Lett. B 615, 231 (2005); Phys. Rev.
Page 118 and 119: violating λ ′′ coupling are co
Page 120 and 121: neutralino-neutrinomassmatrixandins
Page 122 and 123: 4.3 Symmetry Breaking In this secti
Page 124 and 125: +(M 2 +m 2 Σ )ũ2 + ∑ m 2˜ν i
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Here M 1,2 are the soft supersymmet
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is violated, we have neutrino-neutr
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(M 1,2 ,M,µ,Y Σi ,v 1,2 ,ũ,u i )
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In our model in addition to the sta
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4.8 Conclusion In this work we have
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Y Σi √2 ĤuˆΣ 0 0c Rˆν L i
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while the parameter α 1 is α 1 =
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Bibliography [1] S. Roy and B. Mukh
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[15] M. C. Gonzalez-Garcia and J. W
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ν i A Σi • ˜ν i h,H,A × χ
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118
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of the form ⎛ ⎞ A B B m ν =
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triplet representation of A 4 , l =
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m 0 =0.016 m 0 =0.024 m 0 =0.032 2
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Higgs Neutrino mass matrix Eigenval
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5.3. The deviation of the mixing an
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Sin 2 θ 12 Sin 2 θ 13 Sin 2 θ 23
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Figure 5.5: Scatter plot showing th
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Figure 5.6: Same as Fig. 5.5 but fo
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mass matrix is then given as ⎛ m
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Bibliography [1] M. C. Gonzalez-Gar
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140
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142
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a way that the residual µ−τ sym
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where Λ is the cut-off scale of th
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m 2 . The eigenvectors are given as
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For λ ≃ 2 × 10 −2 ≃ λ2 c 2
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2 2 2 1 1 1 y 2 0 y 3 0 y 4 0 -1 -1
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0.08 0.25 0.06 0.2 10 -3 m νee (eV
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We show the values of |U e3 | ≡ s
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while the branching ratio for this
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6.4 The Vacuum Expectation Values I
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where we have defined B = (b+f 1 +f
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VEV alignments. Another way the VEV
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(2006); M. Maltoni, T. Schwetz, M.
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168
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metric standard model in chapter 1.
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mally two. However the R-parity vio
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sector contains the exact/approxima
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PHYS08200604017 Manimala Mitra - Homi Bhabha National Institute

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