Natural Gauge and Gravitational Coupling Unification and the Superpartner Masses

The possibility to achieve unification at the string scale in the context of the simplest supersymmetric grand unified theory is investigated. We find conservative upper bounds on the superpartner masses consistent with the unification of gauge and gravitational couplings, M_{\tilde G} < 5 TeV and M_{\tilde f} < 3 \times 10^7 GeV, for the superparticles with spin one-half and zero, respectively. These bounds hint towards the possibility that this supersymmetric scenario could be tested at future colliders, and in particular, at the forthcoming LHC.Comment: 8 pages, 4 figures, version accepted in Physics Letters

Anomaly-free U(1) gauge symmetries in neutrino seesaw flavor models

Adding right-handed neutrino singlets and/or fermion triplets to the particle content of the Standard Model allows for the implementation of the seesaw mechanism to give mass to neutrinos and, simultaneously, for the construction of anomaly-free gauge group extensions of the theory. We consider Abelian extensions based on an extra U(1)_X gauge symmetry, where X is an arbitrary linear combination of the baryon number B and the individual lepton numbers L_{e,mu,tau}. By requiring cancellation of gauge anomalies, we perform a detailed analysis in order to identify the charge assignments under the new gauge symmetry that lead to neutrino phenomenology compatible with current experiments. In particular, we study how the new symmetry can constrain the flavor structure of the Majorana neutrino mass matrix, leading to two-zero textures with a minimal extra fermion and scalar content. The possibility of distinguishing different gauge symmetries and seesaw realizations at colliders is also briefly discussed.Comment: 12 pages, 2 figures, 7 tables; comments and references added, a new subsection with nonstandard interactions of neutrinos included; final version to appear in Phys. Rev.

Number of fermion generations from a novel Grand Unified model

Electroweak interactions based on a gauge group $\rm SU(3)_L \times U(1)_X$, coupled to the QCD gauge group $\rm SU(3)_c$, can predict the number of generations to be multiples of three. We first try to unify these models within SU(N) groups, using antisymmetric tensor representations only. After examining why these attempts fail, we continue to search for an SU(N) GUT that can explain the number of fermion generations. We show that such a model can be found for $N=9$, with fermions in antisymmetric rank-1 and rank-3 representations only, and examine the constraints on various masses in the model coming from the requirement of unification.Comment: 17 pages, 1 eps figur

SU(5)xSU(5) unification revisited

The idea of grand unification in a minimal supersymmetric SU(5)xSU(5) framework is revisited. It is shown that the unification of gauge couplings into a unique coupling constant can be achieved at a high-energy scale compatible with proton decay constraints. This requires the addition of a minimal particle content at intermediate energy scales. In particular, the introduction of the SU(2)_L triplets belonging to the (15,1)+(\bar{15},1) representations, as well as of the scalar triplet \Sigma_3 and octet \Sigma_8 in the (24,1) representation, turns out to be crucial for unification. The masses of these intermediate particles can vary over a wide range, and even lie in the TeV region. In contrast, the exotic vector-like fermions must be heavy enough and have masses above 10^10 GeV. We also show that, if the SU(5)xSU(5) theory is embedded into a heterotic string scenario, it is not possible to achieve gauge coupling unification with gravity at the perturbative string scale.Comment: 17 pages, 6 figure

Unifying gauge couplings at the string scale

Using the current precision electroweak data, we look for the minimal particle content which is necessary to add to the standard model in order to have a complete unification of gauge couplings and gravity at the weakly coupled heterotic string scale. We find that the addition of a vector-like fermion at an intermediate scale and a non-standard hypercharge normalization are in general sufficient to achieve this goal at two-loop level. Requiring the extra matter scale to be below the TeV scale, it is found that the addition of three vector-like fermion doublets with a mass around 700 GeV yields a perfect string-scale unification, provided that the affine levels are $(k_Y, k_2 ,k_3)=(13/3, 1, 2)$, as in the $SU(5) \times SU(5)$ string-GUT. Furthermore, if supersymmetry is broken at the unification scale, the Higgs mass is predicted in the range 125 GeV - 170 GeV, depending on the precise values of the top quark mass and $\tan \beta$ parameter.Comment: 11 pages, 4 eps figures, using jpconf style, talk given at CORFU2005, RTN meeting ``The Quest for Unification: Theory Confronts Experiment'', 11 - 18 September 2005, Corfu, Greec

Geometrical CP violation from non-renormalisable scalar potentials

We consider in detail the non-renormalisable scalar potential of three Higgs doublets transforming as an irreducible triplet of Delta(27) or Delta(54). We start from a renormalisable potential that spontaneously leads to a vacuum with CP-violating phases independent of arbitrary parameters - geometrical CP violation. Then we analyse to arbitrarily high order non-renormalisable terms that are consistent with the symmetry and we demonstrate that inclusion of non-renormalisable terms in the potential can preserve the geometrical CP-violating vacuum.Comment: 5 pages, 2 figures. v2: references added, accepted by PL

财务治理机制—审计委员会制度研究

本论文属于应用性与实务性的审计研究。 注册会计师对公司财务报告的审计厥为审计理论与实务研究的重心，但注册会计师的审计功能能否充分发挥，核与审计环境有直接且密切的关系。独立、客观与公正固为注册会计师执行业务的基本守则，但确保注册会计师恪守独立、客观、公正的审计环境如果不存在，则社会大众对注册会计师公信力的信任与要求，必然与实际产生差距。1987年，美国不实财务报告全国委员会针对愈来愈多的上市公司财务报告不实与舞弊着手调查，其调查报告即认为财务报告不实与企业内部控制不良、管理当局意图及注册会计师的独立性息息相关；而前二者正与审计环境有关，并且制约了注册会计师的独立性。笔者认为，改善审计环境乃提升...This dissertation studies the applicable auditing theory and practices. The center of auditing theory and practical studies lies in the CPA’s financial report audit. However, the audit environment plays a close and direct role in whether the CPA may fully perform the audit process. Independence, objectiveness and justice are the basic rules of CPAs professional. If such criteria cannot be ensu...学位：管理学博士院系专业：管理学院会计系_会计学学号：B19971101