The dynamics of fermionic unparticles is developed from first principles. It is shown that any unparticle, whether fermionic or bosonic, can be recast in terms of a canonically quantized field, but with non-local interaction terms. We further develop a possible gauge theory for fermionic unparticles. Computing the consequent contribution of un-fermions to the $β$ function of the theory, it is shown that this can be viewed as the sum of two contributions, one fermion-like and the other scalar-like. However, if full conformal invariance is imposed, the latter vanishes identically. We discuss the consequences thereof as well as some general phenomenological issues.
We study the evolution of the gauge coupling and the anomalous dimension of the mass towards an infrared fixed point for non-supersymmetric gauge theories in the modified regularization invariant, RI', scheme. This is done at the three loop level where all the renormalization group functions have been calculated explicitly. The purpose is to assess the scheme dependence of earlier and similar investigations performed at three and four loop order in the modified minimal subtraction, $\bar{\text{MS}}$, scheme. Our results are of the same order when compared to the $\bar{\text{MS}}$ scheme.
We calculate all gauge invariant Barr-Zee type contributions to fermionic electric dipole moments (EDMs) in the two-Higgs doublet models (2HDM) with softly broken Z2 symmetry. We start by studying the tensor structure of h to VV' part in the Barr-Zee diagrams, and we calculate the effective couplings in a gauge invariant way by using the pinch technique. Then we calculate all Barr-Zee diagrams relevant for electron and neutron EDMs. We make bounds on the parameter space in type-I, type-II, type-X, and type-Y 2HDMs. The electron and neutron EDMs are complementary to each other in discrimination…
We revisit the extraction of the triple electroweak gauge boson couplings from the Large Hadron Collider Run I data on the $W^+W^-$ and $W^\pm Z$ productions when the analysis also contains additional operators that modify the couplings of the gauge bosons to light quarks and the gauge boson self-energies. We work in the framework of effective Lagrangians where we consider dimension-six operators and perform a global fit to consistently take into account the bounds on these additional operators originating from the electroweak precision data. We show that the constraints on the Wilson coeffici…
In this paper we do an analysis of the reaction $e^+e^-\to W^+W^-$ for various options of the Next Linear Colliders (NLC), by considering the possibility of deviations from the Standard Model induced by anomalous trilinear vector boson couplings and non-standard fermionic couplings. We show that there are strong correlations among these parameters. By studying the high-energy behaviour of the helicity amplitudes we show that the error made in linearizing the cross-section in the anomalous and non-standard couplings increases with the square of the center of mass energy. We consider also the op…
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…
We explore the Dirac fermionic and complex scalar dark matter in the framework of a hidden $\mathrm{U}(1)_\mathrm{X}$ gauge theory with kinetic mixing between the $\mathrm{U}(1)_\mathrm{X}$ and $\mathrm{U}(1)_\mathrm{Y}$ gauge fields. The $\mathrm{U}(1)_\mathrm{X}$ gauge symmetry is spontaneously broken due to a hidden Higgs field. The kinetic mixing provides a portal between dark matter and standard model particles. Besides, an additional Higgs portal can be realized in the complex scalar case. Dark matter interactions with nucleons are typically isospin violating, and direct detection constr…
Using software under development at Baylor University, we explicitly construct all layer 1 gauge, weakly coupled free fermionic heterotic string models up to order 22 in four large space-time dimensions. The gauge models consist primarily of gauge content making a systematic construction process efficient. We present an overview of the model building procedure, redundancies in the process, methods used to reduce such redundancies and statistics regarding the occurrence of various combinations of gauge group factors and GUT groups. Statistics for both N=4 and N=0 models are presented.
We study a classically scale-invariant model with an electroweak singlet complex scalar mediator together with an anomaly free set of two fermionic dark matters. We introduce $U(1)_X$ gauge symmetry with a new charge $X$ in the dark sector in order to stabilize the mass of the scalar singlet with a new gauge boson. Our conformally invariant scalar potential generates the electroweak symmetry breaking via the Coleman-Weinberg mechanism, and the new scalar singlet acquires its mass through radiative corrections of the fermionic dark matters and the new gauge boson as well as of the SM particles.…
In the type-II seesaw mechanism, the neutrino mass generation could be tested experimentally if the Higgs triplet is at the TeV scale and has a small cubic coupling to the standard model Higgs doublet. We show such small triplet-doublet coupling and the cosmic baryon asymmetry can be simultaneously induced by an additional seesaw mechanism involving a $U(1)_{B-L}$ gauge symmetry. Meanwhile, three neutral fermions for cancelling the gauge anomalies can form a stable Dirac fermionic dark matter besides an acceptably massless fermion.
The implementation of the little Higgs mechanism to solve the hierarchy problem provides an interesting guiding principle to build particle physics models beyond the electroweak scale. Most model building works, however, pay not much attention to the fermionic sector. Through a case example, we illustrate how a complete and consistent fermionic sector of the TeV effective field theory may actually be largely dictated by the gauge structure of the model. The completed fermionic sector has specific flavor physics structure, and many phenomenological constraints on the model can thus be obtained …
We present a fermionic dark matter model mediated by the hidden gauge boson. We assume the QED-like hidden sector which consists of a Dirac fermion and U(1)$_X$ gauge symmetry, and introduce an additional scalar electroweak doublet field with the U(1)$_X$ charge as a mediator. The hidden U(1)$_X$ symmetry is spontaneously broken by the electroweak symmetry breaking and there exists a massive extra neutral gauge boson in this model which is the mediator between the hidden and visible sectors. Due to the U(1)$_X$ charge, the additional scalar doublet does not couple to the Standard Model fermion…
We reconsider the gauge hierarchy problem from the viewpoint of effective field theories and a high-energy physics, motivated by the alternative scenario that the standard model holds up to a high-energy scale such as the Planck scale. The problem is restated as the question whether it is possible to construct a low-energy effective theory and the interaction with heavy particles, without spoiling the structure of a high-energy physics supported by an excellent concept. Based on this reinterpretation, we give a conjecture that theories with hidden fermionic symmetries can be free from the gaug…
The Large N expansion in gauge models with an NJL mechanism is discussed in view of the resulting fermionic mass matrix. A hidden symmetry model is introduced.
We study a left right (LR) extension of the Standard Model (SM) where the Dark Matter (DM) candidate is composed of a set of fermionic Majorana triplets. The DM is stabilized by a remnant $Z_{2}$ symmetry from the breaking of the LR group to the SM. Two simple scenarios where the DM particles plus a certain set of extra fields lead to gauge coupling unification with a low LR scale are explored. The constraints from relic density and predictions for direct detection are discussed for both scenarios. The first scenario with a $SU(2)_R$ vectorlike fermion triplet contains a DM candidate which is …
Two-loop corrections for the form factor in a massive Abelian theory are evaluated, which result from the insertion of massless fermion or scalar loops into the massive gauge boson propagator. The result is valid for arbitrary energies and gauge boson mass. Power-suppressed terms vanish rapidly in the high energy region where the result is well approximated by a polynomial of third order in ln(s/M^2). The relative importance of subleading logarithms is emphasised.
From a deformed AdS$_5$ space, we used the string/gauge duality to study the deep inelastic scattering for unpolarized fermions with spin 1/2, considering the large Bjorken $x$ parameter regime. Here, we also took into account an anomalous dimension of an operator which represents fermions at the boundary. From this analysis, we compute the corresponding structure functions, which are dependent on $x$ and on the photon virtuality $q$. The results achieved are in agreement with the experimental data.
We discuss the unification of gauge couplings within the framework of a wide class of realistic free-fermionic string models which have appeared in the literature, including the flipped SU(5), SO(6)xSO(4), and various SU(3)xSU(2)xU(1) models. If the matter spectrum below the string scale is that of the Minimal Supersymmetric Standard Model (MSSM), then string unification is in disagreement with experiment. We therefore examine several effects that may modify the minimal string predictions. First, we develop a systematic procedure for evaluating the one-loop heavy string threshold corrections i…
Anomalous Dimension of a General Effective Gauge Theory II: Fermionic Sector
PSI Center for Neutron and Muon Sciences（瑞士保罗谢勒研究所中子与缪子科学中心）；Dipartimento di Fisica e Astronomia “G. Galilei”, Università degli Studi di Padova（帕多瓦大学伽利略物理与天文学系）；Istituto Nazionale di Fisica Nucleare, Sezione di Padova（意大利国家核物理研究所帕多瓦分部）
We study a four-dimensional low-energy effective field theory derived from extra dimensional field theories with general gauge backgrounds. We find that products among fermionic zero-modes and lightest scalar modes are expanded by other fermionic zero-modes and lightest scalar modes. Using this aspect, we show that higher-order couplings among the fermionic zero-modes and the lightest scalar mode can be decomposed into three-point couplings. This selection rule originating from a structure of the Dirac-type operators indicates the operator product expansion the underlying conformal field theor…
The fermion-sign problem at finite density is a persisting challenge for Monte-Carlo simulations. Theories that do not have a sign problem can provide valuable guidance and insight for physically more relevant ones that do. Replacing the gauge group SU(3) of QCD by the exceptional group G2, for example, leads to such a theory. It has mesons as well as bosonic and fermionic baryons, and shares many features with QCD. This makes the G2 gauge theory ideally suited to study general properties of dense, strongly-interacting matter, including baryonic and nuclear Fermi pressure effects. Here we pres…
Motivated by the tensions in the Hubble constant $H_0$ and the structure growth $σ_8$ between $Planck$ results and other low redshift measurements, we discuss some cosmological effects of a dark sector model in which dark matter (DM) interacts with fermionic dark radiation (DR) through a light gauge boson (dark photon). Such kind of models are very generic in particle physics with a dark sector with dark gauge symmetries. The effective number of neutrinos is increased by $δN_{eff} \sim 0.5$ due to light dark photon and fermionic DR, thereby resolving the conflicts in $H_0$. The elastic scatter…
We present a model of inflation based on the interaction between a homogeneous and isotropic configuration of a U(1) gauge field and fermionic charge density $\mathcal{J}_{0}$. The regulated fermionic charge density is generated from a Bunch-Davies vacuum state using the methods of Koksma and Prokopec \cite{Koksma:2009tc}, and is found to redshift as $1/a(η)$. The time-like component of gauge field is sourced by the fermionic charge leading to a growth in the gauge field $A(η)_{0}\sim a(η)$. As a result inflation is dominated by the energy density contained in the gauge field and fermionic cha…
We consider the quantum theory of the Lorentzian fermionic differential forms and the corresponding bi-spinor quantum fields, which are the expansion coefficients of the forms in the bi-spinor basis of Becher and Joos [7]. The canonical quantization procedure for the bi-spinor gauge theory in terms of its Dirac spinor constituents is described in detail and the corresponding Feynman rules are derived. We also derive all possible mass terms for massive fermions in the bi-spinor gauge theory. The solutions are classified by a scalar spin quantum number, a number that has no analog in the standar…
We investigate the microphysics of cosmic strings in Nonabelian gauge theories with N=1 supersymmetry. We give the vortex solutions in a specific example and demonstrate that fermionic superconductivity arises because of the couplings and interactions dictated by supersymmetry. We then use supersymmetry transformations to obtain the relevant fermionic zero modes and investigate the role of soft supersymmetry breaking on the existence and properties of the superconducting strings.
We study an effective field theory which includes the Standard Model extended by a Dark Sector consisting of two fermionic $SU(2)_{L}$-doublets. A $Z_2$ parity guarantees that, after electroweak symmetry breaking, the lightest neutral particle is stable, acting as a WIMP. The dark sector interacts with the Higgs and gauge bosons through renormalizable and non-renormalizable $d=5$ operators. We find that a WIMP with a mass around the electroweak scale, i.e. accessible at the LHC, is consistent with collider and astrophysical data only when non-trivial magnetic dipole interactions with the gauge…
I survey the parameter space of NAHE-based free fermionic heterotic string models. First, I discuss flat directions of the low energy effective field theories and show that D-flat directions need not be isomorphic to gauge invariant superpotential terms. Next, I review recent studies of three generation SU(3)_C x SU(2)_L x U(1)_Y, SU(3)_C x SU(2)_L x SU(2)_R x U(1)_B-L, SU(4)_C x SU(2)_L x U(1)_Y', and flipped SU(5) models, constructed by Wilson breaking of the underlying SO(10) observable sector gauge group of the NAHE Z_2 x Z_2 basis. Based on talk presented at the First International Confer…
The fermionic measure in the functional integral of a gauge theory suffers from an ambiguity in the form of a chiral phase. By fixing it, one is led once again to the conclusion that a chiral phase in the quark mass term of QCD has no effect and cannot cause CP violation.
We propose a model of an electrically charged fermion as a regular localized solution of electromagnetic and spinor fields interacting with a physical vacuum, which is phenomenologically described as a logarithmic superfluid. We analytically study the asymptotic behavior of the solution, while obtaining its form by numerical methods. The solution has physically plausible properties, such as finite size, self-energy, total charge and mass. In the case of spherical symmetry, its electric field obeys the Coulomb asymptotics at large distances from its core. It is shown that the observable rest ma…
We systematically study Lorentz symmetry extensions in quantum field theories (QFTs) and their 't Hooft anomalies via cobordism. The total symmetry $G'$ can be expressed in terms of the extension of Lorentz symmetry $G_L$ by an internal global symmetry $G$ as $1 \to G \to G' \to G_L \to 1$. By enumerating all possible $G_L$ and symmetry extensions, other than the familiar SO/Spin/O/Pin$^{\pm}$ groups, we introduce a new EPin group (in contrast to DPin), and provide natural physical interpretations to exotic groups E($d$), EPin($d$), (SU(2)$\times$E(d))/$\mathbb{Z}_2$, (SU(2)$\times$EPin(d))/$\…
The role of scalar boson exchange as a mediator of the fermionic dark particle interaction and the mass of dark particle on the bulk properties of fermionic dark stars including their moment of inertia and tidal deformability are studied. We have found that the role of the attractive nature of the scalar boson exchange and the fermionic dark particle mass can control the stiffness of the fermionic dark star equation of state. By increasing the strength of scalar boson coupling, the fermionic dark star becomes more compact. As a consequence, if scalar boson exchange contribution is included the…
