{[ promptMessage ]}

Bookmark it

{[ promptMessage ]}

rpp2010-rev-leptoquark-quantum-numbers

rpp2010-rev-leptoquark-quantum-numbers - 1 LEPTOQUARKS...

Info icon This preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon
– 1– LEPTOQUARKS Written November 2007 by S. Rolli (Tufts U.) and M. Tanabashi (Nagoya U.) Leptoquarks are hypothetical particles carrying both baryon number (B) and lepton number (L). The possible quantum num- bers of leptoquark states can be restricted by assuming that their direct interactions with the ordinary SM fermions are di- mensionless and invariant under the standard model (SM) gauge group. Table 1 shows the list of all possible quantum numbers with this assumption [1]. The columns of SU (3) C , SU (2) W , and U (1) Y in Table 1 indicate the QCD representation, the weak isospin representation, and the weak hypercharge, respec- tively. The spin of a leptoquark state is taken to be 1 (vector leptoquark) or 0 (scalar leptoquark). Table 1: Possible leptoquarks and their quan- tum numbers. Spin 3 B + L SU (3) c SU (2) W U (1) Y Allowed coupling 0 2 ¯ 3 1 1 / 3 ¯ q c L L or ¯ u c R e R 0 2 ¯ 3 1 4 / 3 ¯ d c R e R 0 2 ¯ 3 3 1 / 3 ¯ q c L L 1 2 ¯ 3 2 5 / 6 ¯ q c L γ μ e R or ¯ d c R γ μ L 1 2 ¯ 3 2 1 / 6 ¯ u c R γ μ L 0 0 3 2 7 / 6 ¯ q L e R or ¯ u R L 0 0 3 2 1 / 6 ¯ d R L 1 0 3 1 2 / 3 ¯ q L γ μ L or ¯ d R γ μ e R 1 0 3 1 5 / 3 ¯ u R γ μ e R 1 0 3 3 2 / 3 ¯ q L γ μ L If we do not require leptoquark states to couple directly with SM fermions, different assignments of quantum numbers become possible [2,3]. Leptoquark states are expected to exist in various extensions of SM. The Pati-Salam model [4] is an example predicting the existence of a leptoquark state. Vector leptoquark states also exist in grand unification theories based on SU (5) [5], CITATION: K. Nakamura et al. (Particle Data Group), JPG 37 , 075021 (2010) (URL: http://pdg.lbl.gov) July 30, 2010 14:34
Image of page 1

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
– 2– SO (10) [6], which includes Pati-Salam color SU (4), and larger gauge groups. Scalar quarks in supersymmetric models with R-parity violation may also have leptoquark-type Yukawa couplings. The bounds on the leptoquark states can therefore be applied to constraining R-parity-violating supersymmetric models. Scalar leptoquarks are expected to exist at TeV scale in extended technicolor models [7,8] where leptoquark states appear as the bound states of techni-fermions. Compositeness of quarks and leptons also provides examples of models which may have light leptoquark states [9]. Bounds on leptoquark states are obtained both directly and indirectly. Direct limits are from their production cross sections at colliders, while indirect limits are calculated from the bounds on the leptoquark-induced four-fermion interactions, which are obtained from low-energy experiments, or from collider experi- ments below threshold.
Image of page 2
Image of page 3
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern