Neutral Vector Boson Research Articles

Complete EFT operator bases for dark matter and weakly-interacting light particle

The standard model can be extended to include weakly-interacting light particle (WILP): real or complex singlet scalar with a conserved U(1) charge, Majorana or Dirac neutral fermion, neutral or hidden-charged vector boson, etc. Imposing the Z2 symmetry, these particles can be lifted as the weakly-interacting massive particle (WIMP), the candidate of dark matter. Instead, imposing the shift symmetry on the scalar components gives rise to the axion-like particle, dark photon, etc. Utilizing these light degrees of freedom along with the standard model particles and imposing different symmetries, we construct the complete and independent sets of effective operators up to dimension eight with the Young tensor technique, consistent with counting from the Hilbert series.

DUNE potential as a new physics probe

Neutrino experiments, in the next years, aim to determine with precision all the six parameters of the three-neutrino standard paradigm. The complete success of the experimental program is, nevertheless, attached to the non-existence (or at least smallness) of Non-Standard Interactions (NSI). In this work, anticipating the data taken from long-baseline neutrino experiments, we map all the weakly coupled theories that could induce sizable NSI, with the potential to be determined in these experiments, in particular DUNE. Once present constraints from other experiments are taken into account, in particular charged-lepton flavor violation, we find that only models containing leptoquarks (scalar or vector) and/or neutral isosinglet vector bosons are viable. We provide the explicit matching formulas connecting weakly coupled models and NSI, both in propagation and production. Departing from the weakly coupled completion with masses at TeV scale, we also provide a global fit on all NSI for DUNE, finding that NSI smaller than 10−2 cannot be probed even in the best-case scenario.

Alternative 3-3-1 models with exotic electric charges

We report the most general classification of 3-3-1 models with β=3 . We found several solutions where anomaly cancellation occurs among fermions of different families. These solutions are particularly interesting as they generate non-universal heavy neutral vector bosons. Non-universality in the standard model fermion charges under an additional gauge group generates charged lepton flavor violation and flavor changing neutral currents; we discuss under what conditions the new models can evade constraints coming from these processes. In addition, we also report the Large Hadron Collider~(LHC) constraints.

NNLO QCD predictions for Z-boson production in association with a charm jet within the LHCb fiducial region

We compute next-to-next-to-leading order (NNLO) QCD corrections to neutral vector boson production in association with a charm jet at the LHC. This process is studied in the forward kinematics at sqrt{s}=13 TeV, which may provide valuable constraints on the intrinsic charm component of the proton. A comparison is performed between fixed order and NLO predictions matched to a parton shower showing mutual compatibility within the respective uncertainties. NNLO corrections typically lead to a reduction of theoretical uncertainties by a factor of two and the perturbative convergence is further improved through the introduction of a theory-inspired constraint on the transverse momentum of the vector boson plus jet system. A comparison between these predictions with data will require an alignment of a flavour-tagging procedure in theory and experiment that is infrared and collinear safe.

Exploring dark Z_d-boson in future large hadron-electron collider

The interaction between the dark U(1)_d sector with the visible Standard Model (SM) sector takes place through the kinetic mixing between the dark photon U(1)_d field Z_d^mu and the SM U(1)_Y gauge field B_mu . After the electroweak and U(1)_d symmetry breaking, the dark photon Z_d^mu acquires a mass and mixes with the SM neutral vector boson Z_mu . This mixing leads to parity-violating coupling between the Z_d^mu and SM. The coupling between the dark photon and SM can be explored in low energy phenomenology as well as in collider experiments. The Lorentz structure of dark photon interaction with SM fermions is explored in the proposed high energy future Large Hadron-electron collider, which would provide efficient energy and a clean environment using cross-section and asymmetries associated with polarisation observable of the dark photon in leptons decay. A chi ^2-analysis is performed to compare the strength of various variables for both the charge- and neutral-current processes. Based on this analysis, 90% confidence level (C.L.) contours in the varepsilon -m_{Z_d} and varepsilon -g_V plane are obtained to put limits on the Z_d^mu mass up to 100 GeV, coupling strength varepsilon and on the Lorentz structure of dark photon coupling with the SM fermions (g_V) at sqrt{s} approx 1.3 TeV.

Corrections to electroweak precision observables from mixings of an exotic vector boson in light of the CDF W -mass anomaly

We enumerate various effective couplings that contribute to the mixings between an exotic vector boson $Z^{\prime}$ and the neutral electroweak vector bosons. The miscellaneous mixing patterns can be evaluated perturbatively. The effective oblique parameters $S^{\prime}$, $T^{\prime}$, and $U^{\prime}$ are calculated to compare with the electroweak precision test results. With the contributions to the non-negligible $U^{\prime}$ parameter from the $\epsilon_{B,W}$ parameters and the aid of some other parameters to cancel the negative $T^{\prime}$, the recent CDF $W$-mass anomaly can therefore be explained.

On (g − 2)μ from gauged U(1)X

We investigate an economical explanation for the (g − 2)μ anomaly with a neutral vector boson from a spontaneously broken U(1)X gauge symmetry. The Standard Model fermion content is minimally extended by 3 right-handed neutrinos. Using a battery of complementary constraints, we perform a thorough investigation of the renormalizable, quark flavor-universal, vector-like U(1)X models, allowing for arbitrary kinetic mixing. Out of 419 models with integer charges not greater than ten, only 7 models are viable solutions, describing a narrow region in model space. These are either Lμ− Lτ or models with a ratio of electron to baryon number close to −2. The key complementary constraints are from the searches for nonstandard neutrino interactions. Furthermore, we comment on the severe challenges to chiral U(1)X solutions and show the severe constraints on a particularly promising such candidate.

HEJ 2.1: High-energy resummation with vector bosons and next-to-leading logarithms

We present version 2.1 of the High Energy Jets (HEJ) event generator for hadron colliders. HEJ is a Monte Carlo generator for processes at high energies with multiple well-separated jets in the final state. To achieve accurate predictions, conventional fixed-order perturbative QCD is supplemented with an all-order resummation of large high-energy logarithms. The new version 2.1 now supports processes with final-state leptons originating from a charged or neutral vector boson together with multiple jets, in addition to processes available in earlier versions. Furthermore, the all-order resummation is extended to include an additional gauge-invariant class of subdominant logarithmic corrections. HEJ 2.1 can be obtained from https://hej.hepforge.org. New version program summaryProgram Title:HEJ.CPC Library link to program files:https://doi.org/10.17632/24c9mb6pf9.2Licensing provisions: GPLv2 or later.Programming language: C++.Journal reference of previous version: Comput. Phys. Commun. 245 (2019) 106832.Does the new version supersede the previous version?: YesReasons for the new version: Support for further scattering processes and inclusion of additional corrections.Summary of revisions: This release adds support for the production of two final-state leptons originating from a charged or neutral vector boson together with multiple jets. Resummation is extended to include next-to-leading logarithmic corrections connected to the emission of additional quark-antiquark pairs.Nature of problem: Conventional event generators for high-energy colliders are based on fixed-order perturbation theory, which converges poorly in regions of phase space with large invariant masses between jets. Reliable predictions in these regions are of general interest, and particularly important whenever cuts relevant to weak-boson fusion or weak-boson scattering are applied.Solution method: The perturbative description can be amended by resumming the high-energy logarithms associated with large invariant masses to all orders in perturbation theory. HEJ 2 implements this resummation following the High Energy Jets framework. Using HEJ 2 in conjunction with a conventional event generator allows one to obtain reliable predictions for processes involving multiple jets in high-energy regions of phase space.Additional comments including restrictions and unusual features: The current version implements multi-jet processes with at most a single lepton pair or Higgs boson in the final state. Matching to fixed-order perturbation theory is currently restricted to leading order.

Magnetized vector boson gas at any temperature

We study the thermodynamic properties of a relativistic magnetized neutral vector boson gas at any temperature. By comparing the results with the low temperature and the non relativistic descriptions of this gas, we found that the fully relativistic case can be separated in two regimes according to temperature. For low temperatures, magnetic field effects dominate and the system shows a spontaneous magnetization, its pressure splits in two components and, eventually, a transversal magnetic collapse might occur. In the high temperature region, the gas behavior is led by pair production. The presence of antiparticles preserves the isotropy in the pressure, and increases the magnetization and the total pressure of the system by several orders. Astrophysical implications of those behaviors are discussed.

Infrared renormalons in kinematic distributions for hadron collider processes

Infrared renormalons in Quantum Chromodynamics are associated with non-perturbative corrections to short distance observables. Linear renormalons, i.e. such that the associated non-perturbative corrections scale like one inverse power of the hard scale, can affect at a non-negligible level even the very high-energy phenomena studied at the Large Hadron Collider. Using an Abelian model, we study the presence of linear renormalons in the transverse momentum distribution of a neutral vector boson Z produced in hadronic collisions. We consider a process where the Z transverse momentum is balanced by a sizable recoil against a coloured final state particle. One may worry that such a colour configuration, not being azimuthally symmetric, could generate unbalanced soft radiation, associated in turn with linear infrared renormalons affecting the transverse momentum distribution of the vector boson. We performed a numerical calculation of the renormalon effects for this process in the so-called large b0 limit. We found no evidence of linear renormalons in the transverse momentum distribution of the Z in the large transverse-momentum region, irrespective of rapidity cuts.

Magnetic properties of a relativistic neutral vector boson gas at any temperature

We study the magnetic properties of a relativistic neutral vector bosons gas under the action of a constant and uniform magnetic field. An analytical expression for the magnetization at any temperature is obtained, and a discussion of the influence of the antiparticles, the vacuum, and the Bose‐Einstein condensation over this magnitude is presented. We analyze the validity of the non‐relativistic and low‐temperature limits and comment on the relevance of our results in astrophysical scenarios.

Resummed Drell-Yan cross-section at N3LL

We present the resummed predictions for inclusive cross-section for Drell-Yan (DY) production as well as onshell Z, W± productions at next-to-next-to-next-to leading logarithmic (N3LL) accuracy. Using the standard techniques, we derive the N-dependent coefficients in the Mellin-N space as well as the N-independent constants and match the resummed result through the minimal prescription procedure with the fixed order results. In addition to the standard ln N exponentiation, we study the numerical impacts of exponentiating N-independent part of the soft function and the complete {overline{g}}_0 that appears in the resummed predictions in N space. All the analytical pieces needed in these different approaches are extracted from the soft-virtual part of the inclusive cross section known to next-to-next-to-next-to leading order (N3LO). We perform a detailed analysis on the scale and parton distribution function (PDF) variations and present predictions for 13 TeV LHC for the neutral Drell-Yan process as well as onshell charged and neutral vector boson productions.

Fermion pair production at e−e+ linear collider experiments in GUT inspired gauge-Higgs unification

Fermion pair production at $e^-e^+$ linear collider experiments with polarized $e^-$ and $e^+$ beams is examined in the GUT inspired $SO(5)\times U(1)\times SU(3)$ gauge-Higgs unification. There arises large parity violation in the couplings of leptons and quarks to Kaluza-Klein (KK) excited neutral vector bosons $Z'$s, which leads to distinctive polarization dependence in cross sections, forward-backward asymmetries, left-right asymmetries, and left-right forward-backward asymmetries in various processes. Those effects are detectable even for the KK mass scale up to about 15 TeV at future $e^-e^+$ linear collider experiments with energies 250$\,$GeV to 1$\,$TeV.

The O(α2) initial state QED corrections to [formula omitted

We calculate the complete O(α2) initial state radiation corrections to e+e− annihilation into a neutral vector boson in a direct analytic computation without any approximation. The corrections are represented in terms of iterated incomplete (elliptic) integrals over alphabets of square-root valued letters. Performing the limit s≫me2, we find discrepancies with the earlier results of Ref. [1] and confirm results obtained in Ref. [2] where the effective method of massive operator matrix elements has been used, which works for all but the power corrections in me2/s. In this way, we also confirm the validity of the factorization of massive partons in the Drell-Yan process to O(α2). We add non–logarithmic terms at O(α2) which have not been considered in previous calculations. The final results in the limit s≫me2 can be given in terms of Nielsen integrals.

Giving mass to the mediating boson of HyperSymmetry by a field transformation applying Higgs mechanism beyond the Standard Model

According to gauge theories, interaction mediating spin-0 bosons must be massless. Theory of hypersymmetry (HySy) predicted massive intermediate bosons. Hypersymmetry field rotation, to be described in this paper, gives mass to the HySy mediating boson. Hysy rotation is performed in the velocity dependent D field – a gauge field defined beyond the Standard Model (SM). Its angle is something similar to the weak mixing Weinberg angle that explains the surplus mass to the neutral weak vector boson; as well as it is similar to the fermion flavour mixing Cabibbo-Kobayashi-Maskawa angles that justify the mass change under weakly interacting quarks’ mixing, respectively. Mass of intermediate bosons must arise from dynamical spontaneous breaking of the group of HySy. The mass of the discussed (fictitious) Goldstone bosons can be removed by the unitarity gauge condition through the Higgs (BEH) mechanism. According to the simultaneous presence of a SM interaction’s symmetry group and the HySy group, their bosons should be transformed together. Spontaneous breakdown of HySy may allow to perform a transformation that does not influence the SM physical state of the investigated system. The paper describes a field transformation that eliminates the mass of the intermediate bosons by the application of the BEH mechanism, rotates the SM and HySy bosons’ masses together, while leaves the SM bosons intact. The result is an angle of precession inclination that characterises the HySy mechanism. In contrast to the known SM intermediate bosons, the HySy intermediate bosons have no fix mass. The mass of the HySy intermediate bosons (that appear as quanta of a velocity dependent gauge field D) depends on the relative velocity of the particles whose interaction they mediate, therefore the derived transformation angle is a function of that velocity.

Vector-boson condensates, spin-triplet superfluidity of paired neutral and charged fermions, and 3P2 pairing of nucleons

After reminding of properties of the condensate of the complex scalar field in the external uniform magnetic field $H$ focus is made on the study of phases of the complex neutral vector boson fields coupled with magnetic field by the Zeeman coupling and phases of the charged vector boson fields. These systems may behave as nonmagnetic and ferromagnetic superfluids and ordinary and ferromagnetic superconductors. Response of the ferromagnetic superfluid and superconducting systems occupying half of space on the external uniform static magnetic field $H$ is thoroughly studied. Then the spin-triplet pairing of neutral fermions at conserved spin is considered. Novel phases are found. In external magnetic field the phase with zero mean spin proves to be unstable to the formation of a phase with a non-zero spin. For $H>H_{\rm cr 2}$ the spin-triplet pairing and ferromagnetic superfluidity continue to exist above the "old" phase transition critical temperature $T_{\rm cr}$. For a certain parameter choice ferromagnetic superfluid phases are formed already for $H=0$, characterized by an own magnetic field $h$. Formation of domains is discussed. Next, spin-triplet pairing of charged fermions is studied. Novel phases are found with a ferromagnetic superconductivity. Then, the 3P$_2$ $nn$ pairing in neutron star matter is studied. Also a 3P$_2$ $pp$ pairing is considered. Numerical estimates are performed in the BCS weak coupling limit and beyond it for the $3P_2$ $nn$ and $pp$ pairings, as well as for the 3S$_1$ $np$ pairing.

Bose‐Einstein condensation and antiparticles in a magnetized neutral vector boson gas at any temperature

AbstractWe study the thermodynamic properties of a relativistic magnetized neutral vector boson gas at any temperature. We analyze the effect of temperature as well as antiparticles in Bose‐Einstein condensation. Astrophysical implications are discussed.

A non-relativistic magnetized vector boson gas at any temperature

We study the thermodynamic properties of a neutral vector boson gas in presence of a constant magnetic field, by means of a semi-classical approach that allows to introduce the spin in the non-relativistic spectrum of the bosons. Bose-Einstein condensation is obtained and it turns out to depend on all the parameters involved in the problem: temperature, particle density and magnetic field. A spontaneous magnetization appears at low temperature as a consequence of the condensed state. The axial symmetry imposed in the system by the magnetic field presence, splits the pressure in two components, one along and another perpendicular to the magnetic axis. Under certain conditions, the perpendicular pressure becomes negative signaling that the system undergoes a transversal magnetic collapse. The spontaneous magnetization might be useful to model magnetic field production inside compact stars, while the negative pressures imposes certain limits to the temperatures and densities needed inside these objects to support a given magnetic field.

The O(α2) initial state QED corrections to e+e− annihilation to a neutral vector boson revisited

We calculate the non-singlet, the pure singlet contribution, and their interference term, at O(α2) due to electron-pair initial state radiation to e+e− annihilation into a neutral vector boson in a direct analytic computation without any approximation. The correction is represented in terms of iterated incomplete elliptic integrals. Performing the limit s≫me2 we find discrepancies with the earlier results of Ref. [1] and confirm results obtained in Ref. [2] where the effective method of massive operator matrix elements has been used, which works for all but the power corrections in m2/s. In this way, we also confirm the validity of the factorization of massive partons in the Drell–Yan process. We also add non-logarithmic terms at O(α2) which have not been considered in [1]. The corrections are of central importance for precision analyses in e+e− annihilation into γ⁎/Z⁎ at high luminosity.

Bounds on lepton flavor violating physics and decays of neutral mesons from τ(μ)→3ℓ , ℓγγ -decays

We study two- and three-body lepton flavor violating (LFV) decays involving leptons and neutral vector bosons $V=\rho^0, \omega, \phi, J/\psi, \Upsilon, Z^0$, as well as pseudo-scalar $P=\pi^0, \eta, \eta', \eta_c$ and scalar $S=f_0(500), f_0(980), a_0(980), \chi_{c0}(1P)$ mesons, without referring to a specific mechanism of LFV realization. In particular, we relate the rates of the three-body LFV decays $\tau(\mu) \to 3 \ell$, where $\ell = \mu$ or $e$, to the two-body LFV decays $(V,P) \to \tau\mu(\tau e, \mu e)$, where $V$ and $P$ play the role of intermediate resonances in the decay process $\tau(\mu) \to 3 \ell$. From the experimental upper bounds for the branching ratios of $\tau(\mu) \to 3 \ell$ decays, we derive upper limits for the branching ratios of $(V,P) \to \tau\mu(\tau e, \mu e)$. We compare our results to the available experimental data and known theoretical upper limits from previous studies of LFV processes, and find that some of our limits are several orders of magnitude more stringent. Using the idea of quark-hadron duality, we extract limits on various quark-lepton dimension-six LFV operators from data on lepton decays. Some of these limits are either new or stronger than those existing in the literature.