<html> <head> <title>Left-Right-Symmetry Processes</title> <link rel="stylesheet" type="text/css" href="pythia.css"/> <link rel="shortcut icon" href="pythia32.gif"/> </head> <body> <h2>Left-Right-Symmetry Processes</h2> At current energies, the world is left-handed, i.e. the Standard Model contains an <i>SU(2)_L</i> group. Left-right symmetry at some larger scale implies the need for an <i>SU(2)_R</i> group. Thus the particle content is expanded by right-handed <i>Z_R^0</i> and <i>W_R^+-</i> and right-handed neutrinos. The Higgs fields have to be in a triplet representation, leading to doubly-charged Higgs particles, one set for each of the two <i>SU(2)</i> groups. Also the number of neutral and singly-charged Higgs states is increased relative to the Standard Model, but a search for the lowest-lying states of this kind is no different from e.g. the freedom already accorded by the MSSM Higgs scenarios. <p/> PYTHIA implements the scenario of [<a href="Bibliography.html" target="page">Hui97</a>]. <p/> The <i>W_R^+-</i> has been implemented as a simple copy of the ordinary <i>W^+-</i>, with the exception that it couples to right-handed neutrinos instead of the ordinary left-handed ones. Thus the standard CKM matrix is used in the quark sector, and the same vector and axial coupling strengths, leaving only the mass as free parameter. The <i>Z_R^0</i> implementation (without interference with the photon or the ordinary <i>Z^0</i>) allows decays both to left- and right-handed neutrinos, as well as other fermions, according to one specific model ansatz. Obviously both the <i>W_R^+-</i> and the <i>Z_R^0</i> descriptions are likely to be simplifications, but provide a starting point. <p/> For the doubly-charged Higgs bosons, the main decay modes implemented are <i>H_L^++ → W_L^+ W_L^+, l_i^+ l_j^+ </i> (<i>i, j</i> generation indices) and <i>H_R^++ → W_R^+ W_R^+, l_i^+ l_j^+</i>. <p/> The right-handed neutrinos can be allowed to decay further. Assuming them to have a mass below that of <i>W_R^+-</i>, they decay to three-body states via a virtual <i>W_R^+-</i>, <i>nu_Rl → l+- f fbar'</i>, where both lepton charges are allowed owing to the Majorana character of the neutrinos. If there is a significant mass splitting, also sequential decays <i>nu_Rl → l+- l'-+ nu'_Rl</i> are allowed. Currently the decays are isotropic in phase space. If the neutrino masses are close to or above the <i>W_R^</i> ones, this description has to be substituted by a sequential decay via a real <i>W_R^</i> (not implemented, but actually simpler to do than the one here). <h3>Production processes</h3> A few different production processes have been implemented, which normally would not overlap and therefore could be run together. <p/><code>flag </code><strong> LeftRightSymmmetry:all </strong> (<code>default = <strong>off</strong></code>)<br/> Common switch for the group of implemented processes within a left-right-symmetric scenario. <p/><code>flag </code><strong> LeftRightSymmmetry:ffbar2ZR </strong> (<code>default = <strong>off</strong></code>)<br/> Scatterings <i>f fbar → Z_R^0</i>. Code 3101. <p/><code>flag </code><strong> LeftRightSymmmetry:ffbar2WR </strong> (<code>default = <strong>off</strong></code>)<br/> Scatterings <i><f fbar' → W_R^+</i>. Code 3102. <p/><code>flag </code><strong> LeftRightSymmmetry:ll2HL </strong> (<code>default = <strong>off</strong></code>)<br/> Scatterings <i>l_i l_j → H_L^--</i>. Code 3121. <p/><code>flag </code><strong> LeftRightSymmmetry:lgm2HLe </strong> (<code>default = <strong>off</strong></code>)<br/> Scatterings <i>l_i gamma → H_L^-- e^+</i>. Code 3122. <p/><code>flag </code><strong> LeftRightSymmmetry:lgm2HLmu </strong> (<code>default = <strong>off</strong></code>)<br/> Scatterings <i>l_i gamma → H_L^-- mu^+</i>. Code 3123. <p/><code>flag </code><strong> LeftRightSymmmetry:lgm2HLtau </strong> (<code>default = <strong>off</strong></code>)<br/> Scatterings <i>l_i gamma → H_L^-- tau^+</i>. Code 3124. <p/><code>flag </code><strong> LeftRightSymmmetry:ff2HLff </strong> (<code>default = <strong>off</strong></code>)<br/> Scatterings <i>f_1 f_2 → H_L^-- f_3 f_4</i> via <i>WW</i> fusion. Code 3125. <p/><code>flag </code><strong> LeftRightSymmmetry:ffbar2HLHL </strong> (<code>default = <strong>off</strong></code>)<br/> Scatterings <i>f fbar → H_L^++ H_L^--</i>. Code 3126. <p/><code>flag </code><strong> LeftRightSymmmetry:ll2HR </strong> (<code>default = <strong>off</strong></code>)<br/> Scatterings <i>l_i l_j → H_R^--</i>. Code 3141. <p/><code>flag </code><strong> LeftRightSymmmetry:lgm2HRe </strong> (<code>default = <strong>off</strong></code>)<br/> Scatterings <i>l_i gamma → H_R^-- e^+</i>. Code 3142. <p/><code>flag </code><strong> LeftRightSymmmetry:lgm2HRmu </strong> (<code>default = <strong>off</strong></code>)<br/> Scatterings <i>l_i gamma → H_R^-- mu^+</i>. Code 3143. <p/><code>flag </code><strong> LeftRightSymmmetry:lgm2HRtau </strong> (<code>default = <strong>off</strong></code>)<br/> Scatterings <i>l_i gamma → H_R^-- tau^+</i>. Code 3144. <p/><code>flag </code><strong> LeftRightSymmmetry:ff2HRff </strong> (<code>default = <strong>off</strong></code>)<br/> Scatterings <i>f_1 f_2 → H_R^-- f_3 f_4</i> via <i>WW</i> fusion. Code 3145. <p/><code>flag </code><strong> LeftRightSymmmetry:ffbar2HRHR </strong> (<code>default = <strong>off</strong></code>)<br/> Scatterings <i>f fbar → H_R^++ H_R^--</i>. Code 3146. <h3>Parameters</h3> The basic couplings of the model are <p/><code>parm </code><strong> LeftRightSymmmetry:gL </strong> (<code>default = <strong>0.64</strong></code>; <code>minimum = 0.0</code>)<br/> lefthanded coupling <i>g_L = e / sin(theta)</i>. <p/><code>parm </code><strong> LeftRightSymmmetry:gR </strong> (<code>default = <strong>0.64</strong></code>; <code>minimum = 0.0</code>)<br/> righthanded coupling <i>g_R</i>, assumed the same as <i>g_L</i>. <p/><code>parm </code><strong> LeftRightSymmmetry:vL </strong> (<code>default = <strong>5.</strong></code>; <code>minimum = 0.0</code>)<br/> vacuum expectation value <i>v_L</i> (in GeV) for the left-triplet. <p/> The corresponding vacuum expectation value <i>v_R</i> is assumed given by <i>v_R = sqrt(2) M_WR / g_R</i> and is not stored explicitly. <p/> The Yukawa couplings of a lepton pair to a <i>H^--</i>, assumed the same for <i>H_L^--</i> and <i>H_R^--</i>, is described by a symmetric 3-by-3 matrix. The default matrix is dominated by the diagonal elements and especially by the <i>tau tau</i> one. <p/><code>parm </code><strong> LeftRightSymmmetry:coupHee </strong> (<code>default = <strong>0.1</strong></code>; <code>minimum = 0.0</code>)<br/> Yukawa coupling for <i>H^-- → e- e-</i>. <p/><code>parm </code><strong> LeftRightSymmmetry:coupHmue </strong> (<code>default = <strong>0.01</strong></code>; <code>minimum = 0.0</code>)<br/> Yukawa coupling for <i>H^-- → mu- e-</i>. <p/><code>parm </code><strong> LeftRightSymmmetry:coupHmumu </strong> (<code>default = <strong>0.1</strong></code>; <code>minimum = 0.0</code>)<br/> Yukawa coupling for <i>H^-- → mu- mu-</i>. <p/><code>parm </code><strong> LeftRightSymmmetry:coupHtaue </strong> (<code>default = <strong>0.01</strong></code>; <code>minimum = 0.0</code>)<br/> Yukawa coupling for <i>H^-- → tau- e-</i>. <p/><code>parm </code><strong> LeftRightSymmmetry:coupHtaumu </strong> (<code>default = <strong>0.01</strong></code>; <code>minimum = 0.0</code>)<br/> Yukawa coupling for <i>H^-- → tau- mu-</i>. <p/><code>parm </code><strong> LeftRightSymmmetry:coupHtautau </strong> (<code>default = <strong>0.3</strong></code>; <code>minimum = 0.0</code>)<br/> Yukawa coupling for <i>H^-- → tau- tau-</i>. </body> </html> <!-- Copyright (C) 2014 Torbjorn Sjostrand -->
