Raul Horvat

Publications (4)0 Total impact

• Article: Forbidden and invisible Z boson decays in covariant theta-exact noncommutative standard model

  Raul Horvat, Amon Ilakovac, Dalibor Kekez, Josip Trampetic, Jiangyabg You
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  ABSTRACT: Triple neutral gauge boson and direct photon-neutrino interactions arise quite naturally in noncommutative gauge field theories. Such couplings are absent in ordinary field theory and imply experimental lower bounds on the energy scale Lambda_NC ~ |theta|^{-1/2} of spacetime noncommutativity. Using non-perturbative methods and a Seiberg-Witten (SW) map based covariant approach to noncommutative gauge theory, we obtain theta-exact expressions for the interactions, thereby eliminating previous restrictions to low-energy phenomena. We discuss implications for Z -> gamma gamma and Z -> nu barnu decays, and show that our results behave reasonably throughout all interaction energy scales. Constraining the invisible Z width for this kind of new physics to be under around 1 MeV, one produces Lambda_NC ~ 140 GeV. Although with the current experimental upper limit on the branching ratio BR(Z -> gamma gamma) the obtained bound on Lambda_NC is of the same order of magnitude, we have demonstrated how the expected improvement on the branching ratio from the LHC experiments may significantly strengthen the bound on the spacetime noncommutativity.
  04/2012;
• Source

  Available from: ArXiv

  Article: Yukawa couplings and seesaw neutrino masses in noncommutative gauge theory

  Raul Horvat, Amon Ilakovac, Peter Schupp, Josip Trampetic, Jiangyang You
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  ABSTRACT: We consider Yukawa couplings in a theta-exact approach to noncommutative gauge field theory and show that both Dirac and singlet Majorana neutrino mass terms can be consistently accommodated. This shows that in fact the whole neutrino-mass extended standard model on noncommutative spacetime can the formulated in the new nonperturbative (in theta) approach which eliminates the previous restriction of Seiberg-Witten map based theories to low-energy phenomena. Spacetime noncommutativity induced couplings between neutrinos and photons as well as Z-bosons appear quite naturally in the model. We derive relevant Feynman rules for the type I seesaw mechanism.
  09/2011;
• Source

  Available from: ArXiv

  Article: Constraining spacetime noncommutativity with primordial nucleosynthesis

  Raul Horvat, Josip Trampetic
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  ABSTRACT: We discuss a constraint on the scale $\Lambda_{\rm NC}$ of noncommutative (NC) gauge field theory arising from consideration of the big bang nucleosynthesis (BBN) of light elements. The propagation of neutrinos in the NC background described by an antisymmetric tensor $\theta^{\mu\nu}$ does result in a tree-level vector-like coupling to photons in a generation-independent manner, raising thus a possibility to have an appreciable contribution of three light right-handed (RH) fields to the energy density of the universe at nucleosynthesis time. Considering elastic scattering processes of the RH neutrinos off charged plasma constituents at a given cosmological epoch, we obtain for a conservative limit on an effective number of additional doublet neutrinos, $\Delta N_\nu =1$, a bound $\Lambda_{\rm NC} \stackrel{>}{\sim}$ 3 TeV. With a more stringent requirement, $\Delta N_\nu \lesssim 0.2$, the bound is considerably improved, $\Lambda_{\rm NC} \stackrel{>}{\sim} 10^3$ TeV. For our bounds the $\theta$-expansion of the NC action stays always meaningful, since the decoupling temperature of the RH species is perseveringly much less than the inferred bound for the scale of noncommutativity. Comment: 4 pages, version to appear in PRD
  01/2009;
• Article: Spacetime noncommutativity and ultrahigh energy cosmic ray experiments

  Raul Horvat, Dalibor Kekez, Josip Trampetić
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  ABSTRACT: If new physics were capable of pushing the neutrino-nucleon inelastic cross section 3 orders of magnitude beyond the standard model prediction, then ultrahigh energy (UHE) neutrinos would have already been observed at neutrino observatories. We use such a constraint to reveal information on the scale of noncommutativity (NC) ΛNC in noncommutative gauge field theories where neutrinos possess a tree-level coupling to photons in a generation-independent manner. In the energy range of interest (1010 to 1011 GeV), the θ expansion (|θ|∼1/ΛNC2) and, therefore, the perturbative expansion, in terms of ΛNC, retains no longer its meaningful character, forcing us to resort to those NC field theoretical frameworks involving the full θ resummation. Our numerical analysis of the contribution to the process coming from the photon exchange impeccably pins down a lower bound on ΛNC to be as high as 900 (450) TeV, depending on the estimates for the cosmogenic neutrino flux. If, on the other hand, one considers a surprising recent result that occurred in Pierre Auger Observatory data, that UHE cosmic rays are mainly composed of highly ionized Fe nuclei, then our bounds get weaker, due to the diminished cosmic neutrino flux. Nevertheless, we show that, even for the very high fraction of heavy nuclei in primary UHE cosmic rays, our method may still yield remarkable bounds on ΛNC, typically always above 200 TeV. Albeit, in this case, one encounters a maximal value for the Fe fraction, from which any useful information on ΛNC can be drawn, delimiting thus the applicability of our method.
  Phys. Rev. D. 83(6).