Relevant Free Parameters Research Articles

Lump solutions to an integrable (3 + 1)-dimensional Boussinesq equation and its dimensionally reduced equations in shallow water

This study uses the Hirota bilinear method and Maple, a symbolic computation program, to derive lump solutions for a new integrable (3 + 1)-dimensional Boussinesq equation and its dimensionally reduced equations. Furthermore, lump solutions with free parameters have been constructed using the dimensionally reduced new form of the (3 + 1)-dimensional Boussinesq equation. The derived lump solutions show it has two trough positions and one crest position. The amplitudes and shapes of lump waves don't vary during propagation but they change their positions. By making three-dimensional, two-dimensional, and density plots for specific values of the relevant free parameters, the propagations of the obtained lump wave solutions are displayed. They also demonstrate how the trough and crest positions of a lump wave change over time with constant velocity. The phase shifts, propagation directions, and energy distributions can be seen from the graphical outputs that the free parameters of the model play a significant role in changing the shapes and amplitudes of the waves. The resulting solutions and their physical characteristics may help to understand how the waves propagate in shallow water in oceanography.

Primordial black holes from multifield inflation with nonminimal couplings

Primordial black holes (PBHs) provide an exciting prospect for accounting for dark matter. In this paper, we consider inflationary models that incorporate realistic features from high-energy physics -- including multiple interacting scalar fields and nonminimal couplings to the spacetime Ricci scalar -- that could produce PBHs with masses in the range required to address the present-day dark matter abundance. Such models are consistent with supersymmetric constructions, and only incorporate operators in the effective action that would be expected from generic effective field theory considerations. The models feature potentials with smooth large-field plateaus together with small-field features that can induce a brief phase of ultra-slow-roll evolution. Inflationary dynamics within this family of models yield predictions for observables in close agreement with recent measurements, such as the spectral index of primordial curvature perturbations and the ratio of power spectra for tensor to scalar perturbations. As in previous studies of PBH formation resulting from a period of ultra-slow-roll inflation, we find that at least one dimensionless parameter must be highly fine-tuned to produce PBHs in the relevant mass-range for dark matter. Nonetheless, we find that the models described here yield accurate predictions for a significant number of observable quantities using a smaller number of relevant free parameters.

The signatures of the new particles h_{2} and Z^{}_{mu tau } at e-p colliders in the {U(1)}_{L^{}_{mu } - L^{}_{tau } } model

Considering the superior performances of the future e-p colliders, LHeC and FCC-eh, we discuss the feasibility of detecting the extra neutral scalar h_{2} and the light gauge boson Z^{}_{mu tau }, which are predicted by the {U(1)}_{L^{}_{mu } - L^{}_{tau }} model. Taking into account the experimental constraints on the relevant free parameters, we consider all possible production channels of h_{2} and Z^{}_{mu tau } at e-p colliders and further investigate their observability through the optimal channels in the case of the beam polarization hbox {P}(e^{-})= -0.8. We find that the signal significance above 5sigma of h_{2} as well as Z^{}_{mu tau } detecting can be achieved via process and a 5sigma sensitivity of Z^{}_{mu tau } detecting can be gained via process at e-p colliders with appropriate parameter values and a designed integrated luminosity. However, the signals of h_{2} decays into pair of SM particles are difficult to be detected.

FIMP dark matter candidate(s) in a B \u2212 L model with inverse seesaw mechanism

The non-thermal dark matter (DM) production via the so-called freeze-in mechanism provides a simple alternative to the standard thermal WIMP scenario. In this work, we consider a popular U(1)B−L extension of the standard model (SM) in the context of inverse seesaw mechanism which has at least one (fermionic) FIMP DM candidate. Due to the added ℤ2 symmetry, a SM gauge singlet fermion, with mass of order keV, is stable and can be a warm DM candidate. Also, the same ℤ2 symmetry helps the lightest right-handed neutrino, with mass of order GeV, to be a stable or long-lived particle by making a corresponding Yukawa coupling very small. This provides a possibility of a two component DM scenario as well. Firstly, in the absence of a GeV DM component (i.e., without tuning its corresponding Yukawa coupling to be very small), we consider only a keV DM as a single component DM, which is produced by the freeze-in mechanism via the decay of the extra Z′ gauge boson associated to U(1)B−L and can consistently explain the DM relic density measurements. In contrast with most of the existing literature, we have found a reasonable DM production from the annihilation processes. After numerically studying the DM production, we show the dependence of the DM relic density as a function of its relevant free parameters. We use these results to obtain the parameter space regions that are compatible with the DM relic density bound. Secondly, we study a two component DM scenario and emphasize that the current DM relic density bound can be satisfied for a wide range of parameter space.

Search for light gauge boson Zμτ via tt̄h1 production at LHC

We consider the production of the new gauge boson [Formula: see text] predicted by the [Formula: see text] model via SM-like Higgs boson [Formula: see text] decaying in the [Formula: see text] production at LHC. Considering the current constraints on the relevant free parameters, we calculate its production cross-section and further investigate the possibility of detecting [Formula: see text] through the process [Formula: see text] at LHC. We find that [Formula: see text] might be detected via this process at LHC with high integrated luminosity.

A signature of anisotropic cosmic-ray transport in the gamma-ray sky

A crucial process in Galactic cosmic-ray (CR) transport is the spatial diffusion due to the interaction with the interstellar turbulent magnetic field. Usually, CR diffusion is assumed to be uniform and isotropic all across the Galaxy. However, this picture is clearly inaccurate: several data-driven and theoretical arguments, as well as dedicated numerical simulations, show that diffusion exhibits highly anisotropic properties with respect to the direction of a background (ordered) magnetic field (i.e., parallel or perpendicular to it). In this paper we focus on a recently discovered anomaly in the hadronic CR spectrum inferred by the Fermi-LAT gamma-ray data at different positions in the Galaxy, i.e. the progressive hardening of the proton slope at low Galactocentric radii. We propose the idea that this feature can be interpreted as a signature of anisotropic diffusion in the complex Galactic magnetic field: in particular, the harder slope in the inner Galaxy is due, in our scenario, to the parallel diffusive escape along the poloidal component of the large-scale, regular, magnetic field. We implement this idea in a numerical framework, based on the DRAGON code, and perform detailed numerical tests on the accuracy of our setup. We discuss how the effect proposed depends on the relevant free parameters involved. Based on low-energy extrapolation of the few focused numerical simulations aimed at determining the scalings of the anisotropic diffusion coefficients, we finally present a set of plausible models that reproduce the behavior of the CR proton slopes inferred by gamma-ray data.

Covariant approach to parametrized cosmological perturbations

We present a covariant formulation for constructing general quadratic actions for cosmological perturbations, invariant under a given set of gauge symmetries for a given field content. This approach allows us to analyze scalar, vector, and tensor perturbations at the same time in a straightforward manner. We apply the procedure to diffeomorphism invariant single-tensor, scalar-tensor, and vector-tensor theories and show explicitly the full covariant form of the quadratic actions in such cases, in addition to the actions determining the evolution of vector and tensor perturbations. We also discuss the role of the symmetry of the background in identifying the set of cosmologically relevant free parameters describing these classes of theories, including calculating the relevant free parameters for an axisymmetric Bianchi-I vacuum universe.

The B − L + xY Model and the Higgs-strahlung Processes at a Collider**Supported by the National Natural Science Foundation of China under Grant Nos 11275088 and 11545012, and the Natural Science Foundation of Liaoning Scientific Committee under Grant No 2014020151.

The gauge extension of the standard model with the symmetry predicts the existence of a light gauge boson with small couplings to ordinary fermions. We discuss its contributions to the muon anomalous magnetic moment . Taking account of the constraints on the relevant free parameters, we further calculate the contributions of the light gauge boson to the Higgs-strahlung processes and .

Simple inhomogeneous cosmological (toy) models

Based on the Lemaître-Tolman-Bondi (LTB) metric we consider two flat inhomogeneous big-bang models. We aim at clarifying, as far as possible analytically, basic features of the dynamics of the simplest inhomogeneous models and to point out the potential usefulness of exact inhomogeneous solutions as generalizations of the homogeneous configurations of the cosmological standard model. We discuss explicitly partial successes but also potential pitfalls of these simplest models. Although primarily seen as toy models, the relevant free parameters are fixed by best-fit values using the Joint Light-curve Analysis (JLA)-sample data. On the basis of a likelihood analysis we find that a local hump with an extension of almost 2 Gpc provides a better description of the observations than a local void for which we obtain a best-fit scale of about 30 Mpc. Future redshift-drift measurements are discussed as a promising tool to discriminate between inhomogeneous configurations and the ΛCDM model.

Comprehensive Spectroscopic Determination of the Crystal Field Splitting in an Erbium Single-Ion Magnet.

The electronic structure of a novel lanthanide-based single-ion magnet, {C(NH2)3}5[Er(CO3)4]·11H2O, was comprehensively studied by means of a large number of different spectroscopic techniques, including far-infrared, optical, and magnetic resonance spectroscopies. A thorough analysis, based on crystal field theory, allowed an unambiguous determination of all relevant free ion and crystal field parameters. We show that inclusion of methods sensitive to the nature of the lowest-energy states is essential to arrive at a correct description of the states that are most relevant for the static and dynamic magnetic properties. The spectroscopic investigations also allowed for a full understanding of the magnetic relaxation processes occurring in this system. Thus, the importance of spectroscopic studies for the improvement of single-molecule magnets is underlined.

Vector bileptons and the decays [formula omitted

Taking into account of the constraints on the relevant parameters from the muon anomalous magnetic moment, we consider the contributions of the vector bileptons V± and U±± predicted by the reduced minimal 331 model to the Higgs decay channels h→γγ and Zγ. Our numerical results show that the vector bileptons can enhance the partial width Γ(h→γγ), while reduce the partial width Γ(h→Zγ), which are anti-correlated. With reasonable values of the relevant free parameters, the vector bileptons can explain the LHC data for the γγ signal. If the CMS data persists, the values of the free parameters λ2 and λ3 should be severe constrained.

Bottom partner [formula omitted] and Zb production at the LHC

Some new physics models, such as “beautiful mirrors” scenario, predict the existence of the bottom partner B′. Considering the constraints from the data for the Z→bb¯ branching ratio Rb and the FB asymmetry AFBb on the relevant free parameters, we calculate the contributions of B′ to the cross section σ(Zb) and the Z polarization asymmetry AZ for Zb production at the LHC. We find that the bottom partner B′ can generate significant corrections to σ(Zb) and AZ, which might be detected in near future.

Production of a neutral scalar associated with a photon at the LHC in the topcolor-assisted technicolor model

In the context of the topcolor-assisted technicolor (TC2) model, we consider the production of the neutral scalar S(π0t or h0t) associated with a photon at the LHC and compare our results with those given by the minimal supersymmetric extension of the Standard Model (MSSM). We find that its production cross section is larger or smaller than that of the scalar particle predicted by the MSSM model, depending on the values of the relevant free parameters.

Exclusive Semi-leptonic Decays b → s(d)νν̄ in the Standard Model with Fourth Generation

We consider the effects of the fourth generation quarks on the rare B decay processes described by the b → s(d)νν̄ processes at the quark level. We find that the values of the branching ratios for some of these rare decay processes are much larger than the standard model (SM) predictions. These processes can be used to constrain the relevant free parameters.

PRODUCTION OF CHARGED HIGGS BOSON ASSOCIATED WITH A W GAUGE BOSON AT THE LHC

Production of charged Higgs boson associated with a W gauge boson at the LHC is mainly induced by the tree-level [Formula: see text] annihilation and the one-loop gg fusion. In the context of the Higgs triplet model (HTM) and the left–right twin Higgs (LRTH) model, we calculate the production cross-section σ of the process pp→H±W∓ and compare our results with those given by supersymmetry (SUSY). We find that, in most of the parameter space of the HTM, the production cross-section σ is smaller than that predicted by the LRTH model or SUSY. The value of σ within the LRTH model is larger or smaller than the SUSY case, which depends on the relevant free parameters.

Single Production of Doubly Charged Higgs Boson via eγ Collision in Higgs Triplet Model

The Higgs triplet model (HTM) predicts the existence of a pair of doubly charged Higgs bosons H±±. Single production of H±± via eγ collision at the next generation e+e− International Linear Collider (ILC) and the Large Hadron electron Collider (LHeC) is considered. The numerical results show that the production cross sections are very sensitive to the neutrino oscillation parameters. Their values for the inverted hierarchy mass spectrum are larger than those for the normal hierarchy mass spectrum at these two kinds of collider experiments. With reasonable values of the relevant free parameters, the possible signals of the doubly charged Higgs bosons predicted by the HTM might be detected in future ILC experiments.

Neutrino-Electron Scattering and the Little Higgs Models

The neutrino-electron scattering process is sensitive to the standard model (SM) and the new physics beyond the SM. We calculate the corrections of the littlest Higgs model and the SU(3) simple group model to the νee scattering cross section. Using the LSND experimental measured values, we obtain the bounds on the relevant free parameters, which might be compatible with those from the electroweak precision data.

Dynamical light vector mesons in low-energy scattering of Goldstone bosons

We present a study of Goldstone boson scattering based on the flavor SU(3) chiral Lagrangian formulated with vector mesons in the tensor field representation. A coupled-channel computation is confronted with the empirical s- and p-wave phase shifts, where good agreement with the data set is obtained up to about 1.2 GeV. There are two relevant free parameters only, the chiral limit value of the pion decay constant and the coupling constant characterizing the decay of the rho meson into a pair of pions. We apply a recently suggested approach that implements constraints from micro-causality and coupled-channel unitarity. Generalized potentials are obtained from the chiral Lagrangian and are expanded in terms of suitably constructed conformal variables. The partial-wave scattering amplitudes are defined as solutions of non-linear integral equations that are solved by means of an N/D ansatz.

The littlest Higgs model with T-parity and some lepton flavor violation decay processes

The new particles predicted by the littlest Higgs model with T-parity (called LHT model) can induce the lepton flavor violation (LFV) couplings at the one-loop level, which can add contributions to some LFV processes. Taking into account the constraints of the experimental data on the relevant free parameters, we calculate the branching ratios of the LFV decay processes Z → \( l\bar l' \) and τ− → µ−P1P2 with P1P2 = π+π−, K+K−, and K0\( \bar K^0 \) in the context of this new physics model. We find that the LHT model can indeed make significant contributions to some of these LFV decay processes. The Z factory option for the future high energy e+e− collider experiments will give severe constraints on the LHT model.

Lepton flavor violation decays τ −→μ − P 1 P 2 in the topcolor-assisted technicolor model and the littlest Higgs model with T-parity

The new particles predicted by the topcolor-assisted technicolor ($TC2$) model and the littlest Higgs model with T-parity (called $LHT$ model) can induce the lepton flavor violation ($LFV$) couplings at tree level or one loop level, which might generate large contributions to some $LFV$ processes. Taking into account the constraints of the experimental data on the relevant free parameters, we calculate the branching ratios of the $LFV$ decay processes $\tau^-\to\mu^- P_1 P_2 $ with $P_1 P_2$ = $\pi^+\pi^-$, $K^+K^-$ and $K^0\bar{K^0}$ in the context of these two kinds of new physics models. We find that the $TC2$ model and the $LHT$ model can indeed produce significant contributions to some of these $LFV$ decay processes.