共查询到20条相似文献,搜索用时 31 毫秒
1.
Precisionmeasurements of Z-boson parameters andW-boson and t-quark masses put strong constraints on non SU(2) × U(1) singlet New Physics.We demonstrate that one extra generation passes electroweak constraints even when all new particle
masses are well above their direct mass bounds. 相似文献
2.
E.-M. Ilgenfritz A. Schiller C. Strecha 《The European Physical Journal C - Particles and Fields》1999,8(1):135-150
We present results for the wave functions and the screening mass spectrum for quantum numbers , and in the three-dimensional SU(2)–Higgs model near to the phase transition line below the endpoint and in the crossover region. Varying the 3D gauge couplings we study the behaviour along a line of constant physics towards the continuum limit in both phases. In the
crossover region the changing spectrum of screening states versus temperature is examined showing the aftermath of the phase
transition at lower Higgs mass. Different to smearing concepts we used large sets of operators with various extensions allowing
to identify wave functions in position space.
Received: 4 August 1998 / Published online: 2 November 1998 相似文献
3.
H.D. Kim J.E. Kim H.M. Lee 《The European Physical Journal C - Particles and Fields》2002,24(1):159-164
Supersymmetric 5D SU(5) grand unification is considered. SU(5) is broken down to by the assignment of the bulk field(s). The matter fields are located at the fixed point(s). In the bulk, a Higgs multiplet (containing the bottom doublet ) and the SU(5) gauge multiplet are located. At one fixed point, (the top doublet) and the standard model matter multiplets are presented. Because of the difference of the locations of and , one can obtain a hierarchy between top and bottom Yukawa couplings. We also present a possible way to understand the s– mass puzzle in this framework of the split multiplet.
Received: 10 December 2001 / Revised version: 22 January 2002 / Published online: 5 April 2002 相似文献
4.
A possible minimal model of the gauge–Higgs unification based on the higher dimensional spacetime M
4⊗(S
1/Z
2) and the bulk gauge symmetry SU(3)
C
⊗SU(3)
W
⊗U(1)
X
is constructed in some detail. We argue that the Weinberg angle and the electromagnetic current can be correctly identified
if one introduces the extra U(1)
X
above and a bulk scalar triplet. The VEV of this scalar as well as the orbifold boundary conditions will break the bulk gauge
symmetry down to that of the standard model. A new neutral zero-mode gauge boson Z′ exists that gains mass via this VEV. We propose a simple fermion content that is free from all the anomalies when the extra
brane-localized chiral fermions are taken into account as well. The issues on recovering a standard model chiral-fermion spectrum
with the masses and flavor mixing are also discussed, where we need to introduce the two other brane scalars which also contribute
to the Z′ mass in the similar way as the scalar triplet. The neutrinos can get small masses via a type I seesaw mechanism. In this
model, the mass of the Z′ boson and the compactification scale are very constrained being, respectively, given in the ranges: 2.7 TeV<m
Z′<13.6 TeV and 40 TeV<1/R<200 TeV. 相似文献
5.
《Physics letters. [Part B]》1987,194(3):385-389
A generalised Z-orbifold model is described in which, as a result of nonstandard embedding of the point group and nontrivial embedding of the discrete translations, the number of generations is reduced to three and the observable gauge group is broken to SUC(3)×SUL(3)×U2(1). Yukawa couplings in this model are also discussed. 相似文献
6.
Existence and uniqueness of the solution are proved for the ‘master equation’ derived from the BPS equation for the vector multiplet scalar in the U(1) gauge theory with N
F charged matter hypermultiplets with eight supercharges. This proof establishes that the solutions of the BPS equations are completely characterized by the moduli matrices divided by the V-equivalence relation for the gauge theory at finite gauge couplings. Therefore the moduli space at finite gauge couplings is topologically the same manifold as that at infinite gauge coupling, where the gauged linear sigma model reduces to a nonlinear sigma model. The proof is extended to the U(N
C) gauge theory with N
F hypermultiplets in the fundamental representation, provided the moduli matrix of the domain wall solution is U(1)-factorizable. Thus the dimension of the moduli space of U(N
C) gauge theory is bounded from below by the dimension of the U(1)-factorizable part of the moduli space. We also obtain sharp estimates of the asymptotic exponential decay which depend on both the gauge coupling and the hypermultiplet mass differences. 相似文献
7.
Hagen Kleinert 《Fortschritte der Physik》1973,21(8):377-396
For any saturation scheme of the chiral SU(2) × SU(2) charge algebra we develop a simple algebraic method of calculating the couplings of ϱ and f trajectories to all particles involved. The information on these coupling is shown to be directly contained in the chiral mass splittings among the different isospin multiplets. 相似文献
8.
Sukanta Dutta Ashok Goyal Mamta 《The European Physical Journal C - Particles and Fields》2009,63(2):305-315
We study the one-loop new physics effects to the CP even triple neutral gauge boson vertices γ
⋆
γ
Z, γ
⋆
Z
Z, Z
⋆
Z
γ and Z
⋆
ZZ in the context of Little Higgs models. We compute the contribution of the additional fermions in Little Higgs models in the
framework of direct product groups where [SU(2)×U(1)]2 gauge symmetry is embedded in SU(5) global symmetry and also in the framework of the simple group where SU(N)×U(1) gauge symmetry breaks down to SU(2)
L
×U(1). We calculate the contribution of the fermions to these couplings when T parity is invoked. In addition, we re-examine the MSSM contribution at the chosen point of SPS1a′ and compare with the SM
and Little Higgs models. 相似文献
9.
Phenomenology of colored radiative neutrino mass model and its implications on cosmic-ray observations
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We extend the colored Zee–Babu model with a gauged U(1)B-L symmetry, and a scalar singlet dark matter(DM) candidate S. The spontaneous breaking of U(1)B-L leaves a residual Z_2 symmetry that stabilizes the DM, and generates a tiny neutrino mass at the two-loop level with the color seesaw mechanism. After investigating the DM and flavor phenomenology of this model systematically, we further focus on its imprint on two cosmic-ray anomalies: The Fermi-LAT gamma-ray excess at the Galactic Center(GCE), and the Pe V ultra-high energy(UHE)neutrino events at the IceCube. We found that the Fermi-LAT GCE spectrum can be well-fitted by DM annihilation into a pair of on-shell singlet Higgs mediators while being compatible with the constraints from the relic density,direct detections, and dwarf spheroidal galaxies, in the Milky Way. Although the UHE neutrino events at the IceCube could be accounted for by the resonance production of a Te V-scale leptoquark, the relevant Yukawa couplings have been severely limited by the current low-energy flavor experiments. We subsequently derive the IceCube limits on the Yukawa couplings by employing its latest six-year data. 相似文献
10.
A. Wirzba Ulf-G Meißner J. A. Oller 《The European Physical Journal A - Hadrons and Nuclei》2003,18(2-3):507-510
We report on how to tackle the problem of establishing a chiral effective field theory in nuclear matter with explicit pion fields and in the presence of external sources (Ann. Phys. 297, 27 (2002)). We have made use of the results of J.A. Oller (Phys. Rev. C 65, 025204 (2002)) where the generating functional for the in-medium chiral SU(2) x SU(2) Lagrangian has been derived. Within this approach we develop the so-called standard power counting rules for the calculation of in-medium pion properties if the residual nucleon energies are of the order of the pion mass. In addition, for the case of vanishing residual nucleon energies, a modified scheme (non-standard counting) is introduced. For both schemes the pertinent scales where the chiral expansions have to break down are established as well. We have performed a systematic analysis of n-point in-medium Green functions up to and including next-to-leading order when the standard rules apply. These include the in-medium contributions to quark condensates, pion propagators, pion masses and couplings of the axial-vector, vector and pseudoscalar currents to pions.Received: 30 September 2002, Published online: 22 October 2003PACS:
12.39.Fe Chiral Lagrangians - 11.30.Rd Chiral symmetries - 21.65. + f Nuclear matter 相似文献
11.
Carlos Castro 《International Journal of Theoretical Physics》2012,51(10):3318-3329
A unification model of 4D gravity and SU(3)×SU(2)×U(1) Yang-Mills theory is presented. It is obtained from a Kaluza-Klein compactification of 8D quaternionic gravity on an internal CP 2=SU(3)/U(2) symmetric space. We proceed to explore the nonlinear connection formalism used in Finsler geometry to show how ordinary gravity in D=4+2 dimensions has enough degrees of freedom to encode a 4D gravitational and SU(5) Yang-Mills theory. This occurs when the internal two-dim space is a sphere S 2. This is an appealing result because SU(5) is one of the candidate GUT groups. We conclude by discussing how the nonlinear connection formalism of Finsler geometry provides an infinite hierarchical extension of the Standard Model within a six dimensional gravitational theory due to the embedding of SU(3)×SU(2)×U(1)⊂SU(5)⊂SU(∞). 相似文献
12.
R. Ramachandran 《Pramana》2005,65(3):381-391
The exotic baryon Θ+(1540 MeV) is visualized as an expected (iso) rotational excitation in the chiral soliton model. It is also argued as a pentaquark
baryon state in a constituent quark model with strong diquark correlations. I contrast these two points of view; observe the
similarities and differences between the two pictures. Collective excitation, the characteristic of chiral soliton model,
points toward small mixing of representations in the wake ofSU (3) breaking. In contrast, constituent quark models prefer near ‘ideal’ mixing, similar to ω-φ mixing. 相似文献
13.
We study the spin- and flavour-dependent SU(6) violations in the baryon spectrum by means of a Gürsey-Radicati mass formula. The average energy of each SU(6) multiplet is described using the SU(6)-invariant interaction given by a hypercentral potential containing a linear and a hyper-Coulomb term. We show that the nonstrange- and strange-baryon masses are, in general, fairly well reproduced and moreover that the Gürsey-Radicati formula holds in a satisfactory way also for the excited states up to 2 GeV. 相似文献
14.
Effects of universal extra dimensions on Standard Model observables first arise at the one-loop level. The quantization of this class of theories is therefore essential in order to perform predictions. A comprehensive study of the SU C(3) × SU L(2) × U Y(1) Standard Model defined in a space-time manifold with one universal extra dimension, compactified on the oribifold $S^1/Z_2$ , is presented. The fact that the four-dimensional Kaluza–Klein theory is subjected to two types of gauge transformations is stressed and its quantization under the basis of the BRST symmetry discussed. A SU C(3) × SU L(2) × U Y(1)-covariant gauge-fixing procedure for the Kaluza–Klein excitations is introduced. The connection between gauge and mass eigenstate fields is established in an exact way. An exhaustive list of the explicit expressions for all physical couplings induced by the Yang–Mills, Currents, Higgs, and Yukawa sectors is presented. The one-loop renormalizability of the standard Green’s functions, which implies that the Standard Model observables do not depend on a cut-off scale, is stressed. 相似文献
15.
《Physics letters. [Part B]》1997,415(1):75-82
We obtain constraints on possible anomalous interactions of the top quark with the electroweak vector bosons arising from the precision measurements at the Z pole. In the framework of SU(2)L ⊗ U(1)Y chiral Lagrangians, we examine all effective CP-conserving operators of dimension five which induce fermionic currents involving the top quark. We constrain the magnitudes of these anomalous interactions by evaluating their one-loop contributions to the Z pole physics. Our analysis shows that the operators that contribute to the LEP observables get bounds close to the theoretical expectation for their anomalous couplings. We also show that those which break the SU(2)C custodial symmetry are more strongly bounded. 相似文献
16.
17.
We analyse, within the “flavoured” leptogenesis scenario of baryon asymmetry generation, the interplay of “low energy” CP-violation,
originating from the PMNS neutrino mixing matrix U, and “high energy” CP-violation, which can be present in the matrix of neutrino Yukawa couplings, λ, and can manifest itself only in “high” energy scale processes. The type I see-saw model with three heavy right-handed Majorana
neutrinos having a hierarchical spectrum is considered. The “orthogonal” parameterisation of the matrix of neutrino Yukawa
couplings, which involves a complex orthogonal matrix R, is employed. In this approach the matrix R is the source of “high energy” CP-violation. Results for normal hierarchical (NH) and inverted hierarchical (IH) light neutrino
mass spectrum are derived in the case of decoupling of the heaviest right-handed Majorana neutrino. It is shown that taking
into account the contribution to Y
B
due to the CP-violating phases in the neutrino mixing matrix U can change drastically the predictions for Y
B
, obtained assuming that only “high energy” CP-violation from the R-matrix is operative in leptogenesis. In the case of the IH spectrum, in particular, there exist significant regions in the
corresponding parameter space where the purely “high energy” contribution in Y
B
plays a subdominant role in the production of baryon asymmetry compatible with the observations.
Also at Institute of Nuclear Research and Nuclear Energy, Bulgarian Academy of Sciences, 1784 Sofia, Bulgaria. 相似文献
18.
Some of the basic problems in neutrino physics, such as new energy scales, the enormous gap between the neutrino masses and
the lightest charged fermion mass, and the possible existence of sterile neutrinos in the eV mass range are studied in the
local gauge group SU
L
(4)×U(1) for electroweak unification, which does not contain fermions with exotic electric charges. It is shown that the neutrino
mass spectrum can be decoupled from that of the other fermions. The further normal seesaw mechanism for neutrinos, with right-handed
neutrino Majorana masses of order M≫M
weak as well a new eV-scale can be accommodated. The eV-scale seesaw may manifest itself in experiments like the Liquid Scintillation
Neutrino Detector (LSND) and MiniBooNE (MB) experimental results and future neutrino experiments. 相似文献
19.
We consider the dynamics governing the evolution of a many body system constrained by a nonabelian local symmetry. We obtain
explicit forms of the global macroscopic condition assuring that at the microscopic level the evolution respects the overall
symmetry constraint. We demonstrate the constraint mechanisms for the case of SU(2) system comprising particles in fundamental, and adjoint representations (‘nucleons’ and ‘pions’).
Received: 10 March 2000 / Revised version: 7 July 2000/ Published online: 8 December 2000 相似文献
20.
We give an elementary treatment of the defining representation and Lie algebra of the three-dimensional unitary unimodular
groupSU(3). The geometrical properties of the Lie algebra, which is an eight dimensional real linear vector space, are developed
in anSU(3) covariant manner. Thef andd symbols ofSU(3) lead to two ways of ‘multiplying’ two vectors to produce a third, and several useful geometric and algebraic identities
are derived. The axis-angle parametrization ofSU(3) is developed as a generalization of that forSU(2), and the specifically new features are brought out. Application to the dynamics of three-level systems is outlined. 相似文献