Broken SU Research Articles

A [formula omitted] standard model

We present a Z2×Z2 orbifold compactification of the E8×E8 heterotic string which gives rise to the exact chiral MSSM spectrum. The GUT breaking SU(5)→SU(3)C×SU(2)L×U(1)Y is realized by modding out a freely acting symmetry. This ensures precision gauge coupling unification. Further, it allows us to break the GUT group without switching on flux in hypercharge direction, such that the standard model gauge bosons can remain massless when the orbifold singularities are blown up. The model has vacuum configurations with matter parity, a large top Yukawa coupling and other phenomenologically appealing features.

Topological dark matter in little Higgs models

We show that certain little Higgs models with symmetry breaking SU(N){yields}SO(N) for N{>=}4 admit topologically stable solitons that may contribute to cosmological dark matter. We have constructed a spherically symmetric soliton and estimated its mass in the case of SU(5){yields}SO(5). Its mass is estimated to be around 10.3 TeV. Whether this particle is a fermion or a boson depends on the value of an integer-valued parameter of the underlying theory, analogous to the number of colors of QCD. In either case, the particle is neutral. If it is a fermion, it is a Majorana particle, which could take part in a seesaw mechanism for neutrino masses.

Monopoles and flux strings from SU(2) adjoint scalars

We construct, in an SU(2) gauge theory with two adjoint scalars, flux strings with monopoles attached at the ends. One scalar breaks SU(2) → U(1) and produces monopoles, the other then breaks the U(1) and produces strings. Dualizing, we write the theory in terms of effective string variables and show that the flux in the string is exactly saturated by the monopoles at the ends.

Coulomb phase gluon scattering at strong coupling

We calculate corrections to gluon scattering amplitudes in a Coulomb phase using gauge/string duality. The Coulomb phase considered is a maximal rank breaking of SU(n1+n2) → SU(n1) × SU(n2) × U(1). This problem therefore has 3 scales involved: 1) the scale of the massive fields MW arising from the spontaneous breaking of the gauge group; 2) The scale of the scattering, characterized by the Mandelstam variables s, t, u; 3) The IR regulator mIR. We find corrections in the hard scattering limit |s|, |t|, |u| >> mIR2 >> MW2, and also find below threshold corrections with MW2 >> |s|, |t|, |u|. We find that the corrections in the second case are finite, and so are IR regulator independent.

New twist on excited dark matter: Implications for INTEGRAL, PAMELA/ATIC/PPB-BETS, DAMA

We show that the 511 keV gamma ray excess observed by INTEGRAL/SPI can be more robustly explained by exciting dark matter (DM) at the center of the galaxy, if there is a peculiar spectrum of DM states chi_0, chi_1 and chi_2, with masses M_0 ~ 500 GeV, M_1 <~ M_0 + 2 m_e, and M_2 = M_1 + delta M >~ M_0 + 2 m_e. The small mass splitting delta M should be <~ 100 keV. In addition, we require at least two new gauge bosons (preferably three), with masses ~100 MeV. With this spectrum, chi_1 is stable, but can be excited to chi_2 by low-velocity DM scatterings near the galactic center, which are Sommerfeld-enhanced by two of the 100 MeV gauge boson exchanges. The excited state chi_2 decays to chi_0 and nonrelativistic e+e-, mediated by the third gauge boson, which mixes with the photon and Z. Although such a small 100 keV splitting has been independently proposed for explaining the DAMA annual modulation through the inelastic DM mechanism, the need for stability of chi_1 (and hence seqestering it from the Standard Model) implies that our scenario cannot account for the DAMA signal. It can however address the PAMELA/ATIC positron excess via DM annihilation in the galaxy, and it offers the possibility of a sharper feature in the ATIC spectrum relative to previously proposed models. The data are consistent with three new gauge bosons, whose couplings fit naturally into a broken SU(2) gauge theory where the DM is a triplet of the SU(2). We propose a simple model in which the SU(2) is broken by new Higgs triplet and 5-plet VEV's, giving rise to the right spectrum of DM, and mixing of one of the new gauge bosons with the photon and Z boson. A coupling of the DM to a heavy Z' may also be necessary to get the right relic density and PAMELA/ATIC signals.

Observation of an in-plane magnetic-field-driven phase transition in a quantum Hall system with SU(4) symmetry

In condensed matter physics, the study of electronic states with SU(N) symmetry has attracted considerable and growing attention in recent years, as systems with such a symmetry can often have a spontaneous symmetry-breaking effect giving rise to a novel ground state. For example, pseudospin quantum Hall ferromagnet of broken SU(2) symmetry has been realized by bringing two Landau levels close to degeneracy in a bilayer quantum Hall system. In the past several years, the exploration of collective states in other multi-component quantum Hall systems has emerged. Here we show the conventional pseudospin quantum Hall ferromagnetic states with broken SU(2) symmetry collapsed rapidly into an unexpected state with broken SU(4) symmetry, by in-plane magnetic field in a two-subband GaAs/AlGaAs two-dimensional electron system at filling factor around $\nu=4$. Within a narrow tilting range angle of 0.5 degrees, the activation energy increases as much as 12 K. While the origin of this puzzling observation remains to be exploited, we discuss the possibility of a long-sought pairing state of electrons with a four-fold degeneracy.

GUT relations from string theory compactifications

Wilson line on a non-simply connected manifold is a nice way to break SU(5) unified symmetry, and to solve the doublet–triplet splitting problem. This mechanism also requires, however, that the two Higgs doublets are strictly vector-like under all underlying gauge symmetries, and consequently there is a limit in a class of modes and their phenomenology for which the Wilson line can be used. An alternative is to turn on a non-flat line bundle in the U ( 1 ) Y direction on an internal manifold, which does not have to be non-simply connected. The U ( 1 ) Y gauge field has to remain in the massless spectrum, and its coupling has to satisfy the GUT relation. In string theory compactifications, however, it is not that easy to satisfy these conditions in a natural way; we call it U ( 1 ) Y problem. In this article, we explain how the problem is solved in some parts of moduli space of string theory compactifications. Two major ingredients are an extra strongly coupled U(1) gauge field and parametrically large volume for compactification, which is also essential in accounting for the hierarchy between the Planck scale and the GUT scale. Heterotic M-theory vacua and F-theory vacua are discussed. This article also shows that the toroidal orbifold GUT approach using discrete Wilson lines corresponds to the non-flat line-bundle breaking above when orbifold singularities are blown up. Thus, the orbifold GUT approach also suffers from the U ( 1 ) Y problem, and this article shows how to fix it.

CHARM MESONS AT FAIR

The in-medium properties of charm mesons (D and [Formula: see text]) in a hot and dense matter are studied. A self-consistent coupled-channel approach is driven by a broken SU(4) s-wave Tomozawa-Weinberg interaction supplemented by an attractive isoscalar-scalar term. As medium effects, we include Pauli blocking, baryon mean-field bindings, and π and open-charm meson self-energies. The dynamically generated [Formula: see text] and [Formula: see text] resonances in the DN sector remain close to their free space position but acquire large widths. The resultant D meson spectral function, which shows a single pronounced quasiparticle peak close to the free mass that broadens with increasing density, also has a long low energy tail associated with smeared [Formula: see text], [Formula: see text] configurations. The low-density approximation for the [Formula: see text] is questionable already at subsaturation densities. We touch upon the implication of our study for J/Ψ suppression at FAIR.

A new class of rank breaking orbifolds

We describe field-theory T 2 / Z n orbifolds that offer new ways of breaking SU ( N ) to lower rank subgroups. We introduce a novel way of embedding the point group into the gauge group, beyond the usual mapping of torus and root lattices. For this mechanism to work the torus Wilson lines must carry nontrivial 't Hooft flux. The rank lowering mechanism proceeds by inner automorphisms but is not related to continuous Wilson lines and does not give rise to any associated moduli. We give a complete classification of all possible SU ( N ) breaking patterns. We also show that the case of general gauge group can already be understood entirely in terms of the SU ( N ) case and the knowledge of standard orbifold constructions with vanishing 't Hooft flux.

Towards a realistic grand gauge-Higgs unification

We investigate a 5D SU ( 6 ) grand gauge-Higgs unification model compactified on an orbifold S 1 / Z 2 . Ordinary quarks and leptons, together with right-handed neutrinos, are just accommodated into a minimal set of representations of the gauge group, without introducing any exotic states in the same representations. The proton decay turns out to be forbidden at least at the tree level. We also find a correct electroweak symmetry breaking SU ( 2 ) L × U ( 1 ) Y → U ( 1 ) em is easily realized by introducing suitable number of adjoint fermions.

Radiative and nonleptonic hyperon decays in broken SU(3)

We report on the recently proposed joint resolution of two long-standing puzzles in weak radiative (WR) and nonleptonic (NL) hyperon decays (HD). First, a good VMD-based description of WRHD is presented. In particular, the large negative asymmetry observed in the Σ+→pγ decay is explained through a calculably large SU(3)-breaking effect in the relevant parity-violating amplitude. Second, the achieved description of the parity-violating WRHD amplitudes permits the extraction, via the SU(2)W+VMD route, of the non-soft-pion correction term in the parity-violating NLHD amplitudes. The latter subtracts a substantial amount from the current-algebra commutator term, thus leading to the resolution of the old S : P discrepancy in NLHD.

Tunneling currents in ferromagnetic systems with multiple broken symmetries

SHORTENED ABSTRACT: A system exhibiting multiple simultaneously broken symmetries offers the opportunity to influence physical phenomena such as tunneling currents by means of external control parameters. In this paper, we consider the broken SU(2) (internal spin) symmetry of ferromagnetic systems coexisting with \textit{i)} the broken U(1) symmetry of superconductors and \textit{ii)} the broken spatial inversion symmetry induced by a Rashba term in a spin-orbit coupling Hamiltonian. In order to study the effect of these broken symmetries, we consider tunneling currents that arise in two different systems; tunneling junctions consisting of non-unitary spin-triplet ferromagnetic superconductors and junctions consisting of ferromagnets with spin-orbit coupling.

Up quark masses from down quark masses

The quark and charged lepton masses and the angles and phase of the CKM mixing matrix are nicely reproduced in a model which assumes SU ( 3 ) ⊗ SU ( 3 ) flavor symmetry broken by the v.e.v.'s of fields in its bi-fundamental representation. The relations among the quark mass eigenvalues, m u / m c ≈ m c / m t ≈ m d 2 / m s 2 ≈ m s 2 / m b 2 ≈ Λ GUT 2 / M Pl 2 , follow from the broken flavor symmetry. Large tan β is required which also provides the best fits to data for the obtained textures. Lepton–quark grandunification with a field that breaks both SU ( 5 ) and the flavor group correctly extends the predictions to the charged lepton masses. The seesaw extension of the model to the neutrino sector predicts a Majorana mass matrix quadratically hierarchical as compared to the neutrino Dirac mass matrix, naturally yielding large mixings and low mass hierarchy for neutrinos.

Two-loop electroweak corrections for four-fermion processes at LHC and ILC

We present the complete analytical result for the two-loop logarithmically enhanced contributions to the high energy asymptotic behavior of the four-fermion cross section in a spontaneously broken SU (2) gauge model. On the basis of this result we derive the dominant two-loop electroweak corrections for the neutral current four-fermion processes at LHC and ILC, such as Drell-Yan dilepton production and Bhabha scattering.

Occupation number formalism for arbitrary Nc baryons

A general method is presented for computing matrix elements of quark operators on baryonic states with low strangeness and arbitrary number of colors N c . These results are useful in applications of the large N c expansion to baryons and exotics. As an application we compute the matrix elements of strangeness changing operators contributing to kaon couplings to ground state baryons and pentaquarks, in broken SU ( 3 ) .

Dynamical coupled-channels approach to hadronic and electromagnetic kaon-hyperon production on the proton

A dynamical coupled-channels formalism for processes $\ensuremath{\pi}N\ensuremath{\rightarrow}\mathit{KY}$ and $\ensuremath{\gamma}N\ensuremath{\rightarrow}\mathit{KY}$ is presented that provides a comprehensive investigation of recent data on the $\ensuremath{\gamma}p\ensuremath{\rightarrow}{K}^{+}\ensuremath{\Lambda}$ reaction. The nonresonant interactions within the subspace $\mathit{KY}\ensuremath{\bigoplus}\ensuremath{\pi}N$ are derived from effective Lagrangians, using a unitary transformation method. The calculations of photoproduction amplitudes are simplified by casting the coupled-channels equations into a form such that the empirical $\ensuremath{\gamma}N\ensuremath{\rightarrow}\ensuremath{\pi}N$ amplitudes are input and only the parameters associated with the $\mathit{KY}$ channel are determined by performing ${\ensuremath{\chi}}^{2}$ fits to all of the available data for ${\ensuremath{\pi}}^{\ensuremath{-}}p\ensuremath{\rightarrow}{K}^{\ifmmode^\circ\else\textdegree\fi{}}\ensuremath{\Lambda},{K}^{\ifmmode^\circ\else\textdegree\fi{}}{\ensuremath{\Sigma}}^{\ifmmode^\circ\else\textdegree\fi{}}$, and $\ensuremath{\gamma}p\ensuremath{\rightarrow}{K}^{+}\ensuremath{\Lambda}$. Good agreement between our models and those data are obtained. In the fits to $\ensuremath{\pi}N\ensuremath{\rightarrow}\mathit{KY}$ channels, most of the parameters are constrained within $\ifmmode\pm\else\textpm\fi{}20%$ of the values given by the Particle Data Group and/or quark model predictions, whereas for $\ensuremath{\gamma}p\ensuremath{\rightarrow}{K}^{+}\ensuremath{\Lambda}$ parameters, ranges compatible with broken SU(6) \ensuremath{\bigotimes} O(3) symmetry are imposed. The main reaction mechanisms in ${K}^{+}\ensuremath{\Lambda}$ photoproduction are singled out and issues related to newly suggested resonances ${S}_{11},{P}_{13}$, and ${D}_{13}$ are studied. Results illustrating the importance of using a coupled-channels treatment are reported. Meson cloud effects on the $\ensuremath{\gamma}N\ensuremath{\rightarrow}{N}^{*}$ transitions are also discussed.

Joint description of weak radiative and nonleptonic hyperon decays in broken SU(3)

We give a joint description of weak radiative (WR) and nonleptonic (NL) hyperon decays (HD) in broken SU(3). The two groups of decays are linked via SU(2){sub W} spin symmetry and vector-meson dominance (VMD). We use experimental information on the parity-conserving NLHD amplitudes to fix the corresponding WRHD amplitudes. With the latter known, the data on the WRHD branching ratios and asymmetries permit us to determine the parity-violating WRHD amplitudes in terms of two parameters corresponding to the two-quark and single-quark transitions. We obtain a good description of the data, and, in particular, a large {sigma}{sup +}{yields}p{gamma} asymmetry. Then, using the SU(2){sub W}+VMD route we determine the non-soft-meson correction term in the parity-violating NLHD amplitudes. The latter is shown to subtract a substantial amount from the current-algebra commutator thus leading towards the resolution of the S ratio P discrepancy in NLHD.

Extended-soft-core baryon-baryon model. II. Hyperon-nucleon interaction

The YN results are presented from the extended soft-core (ESC) interactions. They consist of local and nonlocal potentials because of (i) one-boson exchanges (OBE), which are the members of nonets of pseudoscalar, vector, scalar, and axial mesons; (ii) diffractive exchanges; (iii) two-pseudoscalar exchange; and (iv) meson-pair exchange (MPE). Both the OBE and pair vertices are regulated by Gaussian form factors producing potentials with a soft behavior near the origin. The assignment of the cutoff masses for the baryon-baryon-meson (BBM) vertices is dependent on the SU(3) classification of the exchanged mesons for OBE and a similar scheme for MPE. The particular version of the ESC model, called ESC04 [T. A. Rijken, Phys. Rev. C 73, 044007 (2006)], describes nucleon-nucleon (NN) and hyperon-nucleon (YN) interactions in a unified way using broken SU(3) symmetry. Novel ingredients are the inclusion of (i) the axial-vector meson potentials and (ii) a zero in the scalar- and axial-vector meson form factors. These innovations made it possible for the first time to keep the parameters of the model close to the predictions of the ${}^{3}{P}_{0}$ quark-antiquark creation model. This is also the case for the $F/(F+D)$ ratios. Furthermore, the introduction of the zero helped to avoid the occurrence of unwanted bound states. Broken SU(3) symmetry serves to connect the NN and the YN channels, which leaves after fitting NN only a few free parameters for the determination of the YN interactions. In particular, the meson-baryon coupling constants are calculated via SU(3) using the coupling constants of the NN analysis as input. Here, as a novel feature, medium-strong flavor-symmetry breaking (FSB) of the coupling constants was allowed, using the ${}^{3}{P}_{0}$ model with a Gell-Mann-Okubo hypercharge breaking for the BBM coupling. Very good fits for ESC model with and without FSB were obtained. The charge-symmetry breaking in the $\ensuremath{\Lambda}p$ and $\ensuremath{\Lambda}n$ channels, which is an SU(2) isospin breaking, is included in the OBE, TME, and MPE potentials. Simultaneous fits to the NN- and the YN-scattering data are described, using different options for the ESC model. For the selected 4233 NN data with energies $0\ensuremath{\le}{T}_{\mathrm{lab}}\ensuremath{\le}350$ MeV, a ${\ensuremath{\chi}}^{2}/{N}_{\mathrm{data}}=1.22$ was typically reached. For the usual set of 35 YN data and 3 ${\ensuremath{\Sigma}}^{+}p$ cross sections from a recent KEK experiment E289 ${\ensuremath{\chi}}^{2}/{\mathit{YN}}_{\mathrm{data}}\ensuremath{\approx}0.63$ was obtained. In particular, we were able to fit the precise experimental datum ${r}_{R}=0.468\ifmmode\pm\else\textpm\fi{}0.010$ for the inelastic capture ratio at rest rather well. The four versions (a,b,c, and d) of ESC04 presented in this article, give different results for hypernuclei. The reported G-matrix calculations are performed for YN ($\ensuremath{\Lambda}N,\ensuremath{\Sigma}N,\ensuremath{\Xi}N$) pairs in nuclear matter. The obtained well depths (${U}_{\ensuremath{\Lambda}},{U}_{\ensuremath{\Sigma}},{U}_{\ensuremath{\Xi}}$) reveal distinct features of ESC04a--d. The $\ensuremath{\Lambda}\ensuremath{\Lambda}$ interactions are demonstrated to be consistent with the observed data of ${}_{\ensuremath{\Lambda}\ensuremath{\Lambda}}^{6}$He. The possible three-body effects are investigated by considering phenomenologically the changes of the vector-meson masses.

LACK OF TRINIFICATION IN Z3 ORBIFOLDS OF THE SO(32) HETEROTIC STRING

We report results relating to the trinification scenario in some explicit string constructions that contain SU (3)3 as a gauge symmetry. These models are obtained from symmetric Z3 orbifolds of the SO (32) heterotic string with one discrete Wilson line. We highlight the obstacles that were encountered: the absence of the usual Higgs sector that would break SU (3)3→ SU (3)c× SU (2)L× U (1)Y; the presence of exotics that would generically befoul gauge coupling unification and lead to fractionally-charged states in the low energy spectrum.

One-loop renormalization group equations for two left-right supersymmetric models

In this paper we present the renormalization group equations to one-loop order for all the parameters of two supersymmetric left-right theories that are softly broken. Both models are based upon the gauge group SU(3)^c x SU(2)_L x SU(2)_R x U(1)_{B - L} and both contain an arbitrary number of bidoublets as well as singlets; however, one model uses doublets to break SU(2)_R and the other uses triplets.