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B. Bajc

Publications and source records attributed to B. Bajc.

16 recordsLinked to original sources
arXiv2012

Realistic Fermion Masses and Nucleon Decay Rates in SUSY SU(5) with Vector-Like Matter

We show that by adding a vector-like 5+5bar pair of matter fields to the spectrum of the minimal renormalizable SUSY SU(5) theory the wrong relations for fermion masses can be corrected, while being predictive and consistent with proton lifetime limits. Threshold correction from the vector-like fields improves unification of gauge couplings compared to the minimal model. It is found that for supersymmetric spectra lighter than 3 TeV, which would be testable at the LHC, at least some of the nucleon decay modes should have partial lifetimes shorter than about 2.10^34 yrs., which is within reach of ongoing and proposed experiments.

hep-ph↗
arXiv2010

The Hunt for New Physics at the Large Hadron Collider

The Large Hadron Collider presents an unprecedented opportunity to probe the realm of new physics in the TeV region and shed light on some of the core unresolved issues of particle physics. These include the nature of electroweak symmetry breaking, the origin of mass, the possible constituent of cold dark matter, new sources of CP violation needed to explain the baryon excess in the universe, the possible existence of extra gauge groups and extra matter, and importantly the path Nature chooses to resolve the hierarchy problem - is it supersymmetry or extra dimensions. Many models of new physics beyond the standard model contain a hidden sector which can be probed at the LHC. Additionally, the LHC will be a top factory and accurate measurements of the properties of the top and its rare decays will provide a window to new physics. Further, the LHC could shed light on the origin of neutralino masses if the new physics associated with their generation lies in the TeV region. Finally, the LHC is also a laboratory to test the hypothesis of TeV scale strings and D-brane models. An overview of these possibilities is presented in the spirit that it will serve as a companion to the Technical Design Reports (TDRs) by the particle detector groups ATLAS and CMS to facilitate the test of the new theoretical ideas at the LHC. Which of these ideas stands the test of the LHC data will govern the course of particle physics in the subsequent decades.

hep-ph↗
arXiv2008

Flavour physics of leptons and dipole moments

This chapter of the report of the ``Flavour in the era of the LHC'' Workshop discusses the theoretical, phenomenological and experimental issues related to flavour phenomena in the charged lepton sector and in flavour-conserving CP-violating processes. We review the current experimental limits and the main theoretical models for the flavour structure of fundamental particles. We analyze the phenomenological consequences of the available data, setting constraints on explicit models beyond the Standard Model, presenting benchmarks for the discovery potential of forthcoming measurements both at the LHC and at low energy, and exploring options for possible future experiments.

hep-ph↗
arXiv2004

Proceedings to the 'Euroconference on Symmetries Beyond the Standard Model',12. - 17. July 2003, Portoroz, Slovenia (Part 2 of 2)

Contents of Part 2: 11. Supersymmetric Grandunification and Fermion Masses (B. Bajc) 12. General Principles of Brane Kinematics and Dynamics (M. Pavsic) 13. Cosmological Neutrinos (G. Mangano) 14. The Problem of Mass (C.D. Froggatt) 15. How to Approach Quantum Gravity ... (D. Grumiller and W. Kummer) 16. Hidden Spacetime Symmetries and Generalized Holonomy in M-theory (M.J. Duff and J.T. Liu) 17. On the Resolution of Space-Time Singularities II (M. Maceda and J. Madore) 18. The Multiple Point Principle (D.L. Bennett and H.B. Nielsen) 19. Dynamics of Glue-Balls in N = 1 SYM Theory (L. Bergamin) 20. Quantization of Systems with Continuous Symmetries ... (M.V. Chichikina) 21. Singular Compactifications and Cosmology (L. Jaerv, T. Mohaupt and F. Saueressig) 22. Fundamental Physics and Lorentz Violation (R. Lehnert) 23. Functional Approach to Squeezed States ...(L. Musongela) 24. Constraining the Curvaton Scenario (M. Postma) 25. D-Branes and Unitarity of Noncommutative Field Theories (A. Torrielli) 26. Spinorial Cohomology and Supersymmetry (D. Tsimpis) (Contents of Part 1: 1. Status of the Standard Model(P.H. Frampton), 2. Cosmological Constraints from MBA and Polarization (A. Melchiorri), 3. AdS/CFT Correspondence and Unification at About 4 TeV (P.H. Frampton), 4. New Solutions in String Field Theory (L. Bonora), 5. The Approach Unifying Spins and Charges (A. Borstnik Bracic and N. Mankoc Borstnik) 6. An Example ... (N. Mankoc Borstnik and H.B. Nielsen) 7. Hierarchy Problem and a New Bound State(C.D. Froggatt and H.B. Nielsen) 8. What Comes Next? (Q. Shafi)9. Loops Versus Strings (E. Alvarez) 10. Fuzzy Two-dimensional Spaces(F. Lizzi))

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arXiv1998

The CP violating asymmetry in $B^{\pm} \to M {\bar M} π^{\pm}$ decays

We analyze the asymmetry in the partial widths for the decays $B^{\pm} \to M {\bar M} π^{\pm}$ ($ M = π^+, K ^+, π^0, η$), which results from the interference of the nonresonant decay amplitude with the resonant amplitude for $B^{\pm} \to χ_{c0} π^{\pm} $ followed by the decay $χ_{c0} \to M {\bar M} $. The CP violating phase $γ$ can be extracted from the measured asymmetry. We find that the partial width asymmetry for $B^\pm \to π^+ π^- π^\pm$ is about $0.33~sin γ$, and about $0.45~ sin γ$ for $B^\pm \to K^+ K^-π^\pm$, while it is somewhat smaller for $B^\pm \to π^0 π^0 π^\pm$ and $B^\pm \to ηηπ^\pm$. Potential sources of uncertainties in these results, primarily coming from poorly known input parameters, are discussed.

hep-ph↗
arXiv1998

Signal for CP violation in $B^{\pm} \to P {\bar P} π^{\pm}$ decays

We analyze the partial rate asymmetry in $B^{\pm} \to P {\bar P} π^{\pm}$ decays ($ P = π^+, K ^+, π^0, η$) which results from the interference of the nonresonant decay amplitude and the resonant amplitude for $B^{\pm} \to χ_{c0} π^{\pm} $ followed by the decay $χ_{c0} \to P {\bar P} $. The CP violating phase $γ$ can be extracted from the measured asymmetry. We find that the partial rate asymmetry for $B^\pm \to π^+ π^- π^\pm$ is $0.33~sin γ$, while for $B^\pm \to K^+ K^-π^\pm$ it amounts $0.45~ sin γ$.

hep-ph↗
arXiv1998

Resonant and nonresonant D+ -> K- pi+ l+ nu(l) semileptonic decays

We analyse the semileptonic decay D+ -> K- pi+ l+ nu(l) using an effective Lagrangian developed previously to describe the decays D -> P l nu(l) and D -> V l nu(l). Light vector mesons are included in the model which combines the heavy quark effective Lagrangian and chiral perturbation theory approach. The nonresonant and resonant contributions are compared. With no new parameters the model correctly reproduces the measured ratio Gamma(nres)/Gamma(nres + res). We also present useful nonresonant decay distributions. Finally, a similar model, but with a modified current which satisfies the soft pion theorems at the expense of introducing another parameter, is analyzed and the results of the models are compared.

hep-ph↗
arXiv1997

Nonleptonic two-body charmed meson decays in an effective model for their semileptonic decays

We analyze $D \to P V$, $D \to PP$ and $D \to VV$ decays within a model developed to describe the semileptonic decays $D \to V l ν_l$ and $D\to P l ν_l$. This model combines the heavy quark effective Lagrangian and chiral perturbation theory. We determine amplitudes for decays in which the direct weak annihilation of the initial $D$ meson is absent or negligible, and in which the final state interactions are small. This analysis reduces the arbitrariness in the choice of model parameters. The calculated decay widths are in good agreement with the experimental results.

hep-ph↗
arXiv1996

SU(3) flavor symmetry breaking and semileptonic decays of heavy mesons

Assuming the ${\bar D}^0, D^-, D^-_s$ and $B^+, B^0, B_s^0$ mesons belong to triplets of SU(3) flavor symmetry, we analyse the form factors in the semileptonic decays of these mesons. Both quark and meson mass differences are taken into account. We find a number of relations, in agreement with the present data as well as with previous analyses, and predict certain ratios of form factors, not yet measured, most notably the D meson decay constant $f_D = 209 \pm 39$ MeV.

hep-ph↗
arXiv1996

Low-energy dynamics of the $γγ\toππ$ reaction

We calculate the one-quark-loop amplitude for the low energy $γγ\toππ$ collision in the context of the Nambu and Jona-Lasinio model with scalar and pseudoscalar four quark couplings to all orders in the external momenta. We show that the NJL predictions for the $γγ\toπ^+π^-$ reaction are not far from the Born amplitude, which is close to the data, and is compatible with the chiral perturbation theory estimations. We determine the corrections given by the NJL model in leading order of $1/N_c$ to the chiral loop amplitude for $γγ\toπ^0π^0$. Numerical results for the $γγ\rightarrowππ$ cross sections and for pion polarizabilities are given.

hep-ph↗
arXiv1995

An effective model for charmed meson semileptonic decays

We analyze charm meson semileptonic decays using the measured ratios $Γ_L/Γ_T$ and $Γ_{+}/Γ_{-}$ from $D\to {\bar K}^{*}$ and the branching ratios for $D \to {\bar K}^{*}$ and $D \to {\bar K}$. First we introduce the light vector mesons in a model which combines the heavy quark effective Lagrangian and the chiral perturbation approach. We propose a method which predicts the behavior of the form factors. Using the available experimental data we determine the values of some model parameters and reproduce the observed branching ratios for $D_{s} \to Φ$, $D_{s} \to (η+ η^{\prime})$ and $D \to π$. We make predictions for the yet unmeasured branching ratios and polarization observables.

hep-ph↗
arXiv1995

$c\to u γ$ in Cabibbo suppressed D meson radiative weak decays

We investigate Cabibbo suppressed $D^{0}$, $D^{+}$ and $D^{+}_{s}$ radiative weak decays in order to find the best mode to test $c\to u γ$ decay. Combining heavy quark effective theory and the chiral Lagrangian approach we determine the decay widths. We calculate $Γ(D^{0}\to ρ^{0}/ωγ)/ Γ(D^{0}\to {\bar K}^{*0} γ)$ previously proposed to search for possible New Physics. However, we notice that there are large, unknown, corrections within the Standard Model. We propose a better alternative, the ratio $Γ(D_{s}^{+}\to K^{*+} γ)/ Γ(D_{s}^{+}\to ρ^{+} γ)$, and show that it is less sensitive to the Standard Model.

hep-ph↗
arXiv1995

Charm meson radiative decays

Combining heavy quark effective theory and the chiral Lagrangian approach we investigate D meson radiative decays. First, we reanalyse $D^{*} \rightarrow D γ$ decays using heavy quark spin symmetry, chiral symmetry Lagrangian, but including also the light vector mesons. Then, we calculate branching ratios $D \rightarrow V γ$. We make some comments on the Cabbibo suppressed decays $D \to ρ/ ωγ$ and the branching ratios of $D \rightarrow P P γ$ decays.

hep-ph↗
arXiv1994

Vector and pseudoscalar charm meson radiative decays

Combining heavy quark effective theory and the chiral Lagrangian approach we investigate radiative decays of pseudoscalar $D$ mesons. We first reanalyse $D^{*} \rightarrow D γ$ decays within the effective Lagrangian approach using heavy quark spin symmetry, chiral symmetry Lagrangian, but including also the light vector mesons. We then investigate $D \rightarrow V γ$ decays and calculate the $D^0 \rightarrow \bar{K}^{*0} γ$ and $D^{s+} \rightarrow ρ^+ γ$ partial widths and branching ratios.

hep-ph↗