The fermion propagator in an arbitrary covariant gauge can be obtained from the Landau gauge result via a Landau-Khalatnikov-Fradkin transformation. This transformation can be written in a practically useful form in both configuration and momentum space. It is therefore possible to anticipate effects of a gauge transformation on the propagator's analytic properties. These facts enable one to establish that if a critical number of flavours for chiral symmetry restoration and deconfinement exists in noncompact QED3, then its value is independent of the gauge parameter. This is explicated using simple forms for the fermion-photon vertex and the photon vacuum polarisation. The illustration highlights pitfalls that must be avoided in order to arrive at valid conclusions. Landau gauge is seen to be the covariant gauge in which the propagator avoids modification by a non-dynamical gauge-dependent exponential factor, whose presence can obscure truly observable features of the theory.
The idea of unification attempts to explain the structure of the Standard Model (SM) in terms of fewer fundamental forces and/or matter fields. However, traditional grand unified theories based on $SU(5)$ and $\mathrm{Spin}(10)$ shed no light on the existence of three generations of fermions, nor the distinctive pattern of their Yukawa couplings to the Higgs. We discuss two routes for unifying the SM gauge symmetry with its flavour symmetries: firstly, unifying flavour with electroweak symmetries via the group $SU(4) \times Sp(6)_L \times Sp(6)_R$; secondly, unifying flavour and colour via $SU…
Extensions of the Standard Model with an Abelian gauge group are constrained by gauge anomaly cancellation, so that only a limited number of possible charge assignments is allowed without the introduction of new chiral fermions. For flavour universal charges, couplings of the associated hidden photon to Standard Model fermions are flavour conserving at tree-level. We show explicitly that even the flavour specific charge assignments allowed by anomaly cancellation condition lead to flavour conserving tree-level couplings of the hidden photon to quarks and charged leptons \emph{if} the CKM or PM…
A framework based on a class of abelian gauge symmetries is proposed in which the masses of only the third generation quarks and leptons arise at the tree level. The fermions of the first and second families receive their masses through radiative corrections induced by the new gauge bosons in the loops. It is shown that the class of abelian symmetries which can viably implement this mechanism are flavour non-universal in nature. Taking the all-fermion generalization of the well-known leptonic $L_μ-L_τ$ and $L_e - L_μ$ symmetries, we construct an explicit renormalizable model based on two $U(1)…
Searching for New Physics through correlations of Flavour Observables
即将到来的味道精确时代将允许在不同的新物理场景中发现各种味道违规模式。我们讨论不同的类。标准模型的一个简单扩展是在SM规范群中增加一个U（1）规范对称性，它通常会引入新的味源、CP破坏和右手流。在这样的Z'模型中，各种风味可观察量之间的相关性出现，可以测试和区分不同的Z'场景。一个具有味破坏Z'耦合的具体模型是基于规范群SU（3）_C x SU（3）_L x U（1）_X的331模型。我们还研究了由重中性标量和/或伪标量H^0（A^0）介导的树水平FCNC。此外，还简要讨论了一个额外的近似整体U（2）^3味对称性的含义。最后给出了一个具有矢量费米子和味破坏Z耦合的模型。我们确定了一些不同的约束最小味道违反（CMFV）模型，可以测试和区分这些不同的情况下，不同的观测值之间的相关性。
We consider scenarios with a heavy $Z^\prime$ gauge boson with flavour non-universal quark and lepton couplings with the goal to illustrate how the cancellation of gauge anomalies generated by the additional U(1)$^\prime$ gauge symmetry would imply correlations between FCNC processes in the quark sector, in the lepton sector and most interestingly between quark flavour and lepton flavour violating processes. We present scenarios with only left-handed flavour-violating $Z^\prime$ couplings and those with also right-handed flavour-violating couplings. These are characterized by a small number of…
Composite Higgs models are promising candidate models to address the long-standing naturalness problem in the Standard Model. Among them, the most minimal one is the SU(2) with 2 flavours of fermions in the fundamental representation of the gauge group. An important prediction in these models is the existence of resonance spectrum in vector boson scattering. Here we study the lowest such resonance, which is the equivalent of rho resonance in QCD. We describe the scan of the parameter space using the clover-improved Wilson fermions with Symanzik improved gauge action and then show the first res…
KTH Royal Institute of Technology（皇家理工学院）；Instituto de Física Teórica UAM/CSIC, Universidad Autónoma de Madrid（马德里自治大学理论物理研究所）；Universidad Complutense de Madrid（马德里康普顿斯大学）；Universidad de Castilla-La Mancha（卡斯蒂利亚-拉曼恰大学）
We propose an Abelian gauged version of the singlet-doublet fermionic dark matter (DM) model where DM, combination of a vector like fermion doublet and a fermion singlet, is naturally stabilised by the gauge symmetry without requiring any ad-hoc discrete symmetries. In order to have good detection prospects at collider experiments like the large hadron collider (LHC) and enlarged parameter space for low mass DM, we consider the additional gauge symmetry to be based on the quantum $B-3L_τ$ where the restriction to third generation of leptons is chosen to have weaker bounds from the LHC on the c…
Minimal complete tri-hypercharge theories of flavour
School of Physics & Astronomy, University of Glasgow（格拉斯哥大学物理与天文学学院）；School of Physics & Astronomy, University of Southampton（南安普顿大学物理与天文学学院）；Instituto de Física Corpuscular, CSIC-Universitat de València（瓦伦西亚大学-CSIC粒子物理研究所）；Departament de Física Teòrica, Universitat de València（瓦伦西亚大学理论物理系）
本文提出两种最小的三超荷理论，通过三个物理尺度解释费米子质量和混合，且所有基本系数为$\mathcal{O}(1)$，并探讨其在LHC Run 3中的实验可探测性。
