Viable Parameter Research Articles

Collider signatures of a scalar leptoquark and vectorlike lepton in light of muon anomaly

Despite the immense success of the Standard Model (SM), the hunt for physics beyond the Standard Model (BSM) has continued. Extension of the SM gauge group or the particle content of the SM remains a viable solution to many observed anomalies, such as the anomalous magnetic moment of muon, flavor violation, dark matter, etc. In this work, we consider a BSM model which includes a leptoquark, a vectorlike lepton, and a real scalar singlet. The model accounts for a dark matter candidate through a ${\mathbb{Z}}_{2}$ symmetry in addition to predicting the muon ($g\ensuremath{-}2$) in agreement with the experimental measurement. We also show that the experimental measurements of the lepton flavor violation are satisfied in a wide range of parameter space. The viable parameter space of the model is used to study the collider signatures arising from the pair production of the leptoquark in the $2\ensuremath{\mu}+2b+{\overline{)E}}_{T}$ channel at the 14 TeV LHC run.

Minimal Nambu-Goldstone-Higgs model in supersymmetric SU(5) revisited

We revisit the minimal Nambu-Goldstone (NG) Higgs supersymmetric (SUSY) SU(5) grand unified model and study its phenomenological implications. The Higgs sector of the model possesses a global SU(6) symmetry, which is spontaneously broken and results in the Higgs doublets of the minimal SUSY Standard Model (MSSM) as NG chiral superfields. Therefore, the model naturally leads to light Higgs doublets and solves the doublet-triplet splitting problem. Because of the SU(6) symmetry, the couplings of the Higgs sector are tightly restricted, and thus the model is more predictive than the minimal SUSY SU(5). We determine all the grand-unified-theory parameters via the matching conditions of the gauge coupling constants at the unification scale and calculate proton lifetime, confronting this with current experimental bounds. We discuss that this model is incompatible with the constrained MSSM, whilst it has a large viable parameter space in the high-scale SUSY scenario. The perturbativity condition on the trilinear coupling of the adjoint Higgs field imposes an upper (lower) limit on the wino (gluino) mass, implying a hierarchical mass pattern for these gauginos. Future proton-decay searches can probe a large part of the parameter space, especially if the SUSY-breaking scale is $\lesssim 100$~TeV.

Charged lepton flavor violating radiative decays li→ ljγ in G2HDM

We compute the electromagnetic form factors of the liljγ vertex at one-loop level in the minimal G2HDM which has a sub-GeV vector dark matter candidate. The results are applied to the radiative decay rates for the charged lepton flavor violating processes li → ljγ, and the anomalous magnetic dipole moment and the electric dipole moment of the charged lepton. To numerically compute the branching ratio for μ → eγ and compare with the latest experimental limit from MEG, we adapt our previous parameter space scan that is consistent with the relic density and constraints from direct searches of dark matter, W and Z mass measurements, as well as the LHC Higgs signal strengths and invisible width. While the extra contributions are at least an order of magnitude smaller than required to explain the ~4.2σ discrepancy in the muon anomaly, the existing MEG limit imposes stringent constraint on the parameter space. The remaining viable parameter space can be further probed by the MEG II sensitivity for μ → eγ as well as from the direct searches of sub-GeV dark matter in foreseeable future. Higher loop contributions may be significant to resolve the discrepancy in the muon anomaly and generate a non-vanishing electric dipole moments for the standard model quarks and leptons in G2HDM.

A scotogenic model with two inert doublets

In this work, we present a scotogenic model, where the neutrino mass is generated at one-loop diagrams. The standard model (SM) is extended by three singlet Majorana fermions and two inert scalar doublets instead of one doublet as in the minimal scotogenic model. The model scalar sector includes two CP-even, two CP-odd and two charged scalars in addition to the Higgs. The dark matter (DM) candidate could be either the light Majorana fermion (Majorana DM), or the lightest among the CP-even and the CP-odd scalars (scalar DM). We show that the model accommodates both Majorana and scalar DM within a significant viable parameter space, while considering all the relevant theoretical and experimental constraints such as perturbativity, vacuum stability, unitarity, the di-photon Higgs decay, electroweak precision tests and lepton flavor violating constraints. In addition to the collider signatures predicted by the minimal scotogenic model, our model predicts some novel signatures that can be probed through some final states such as .

Disentangling the high- and low-cutoff scales via the trilinear Higgs couplings in the type-I two-Higgs-doublet model

The type-I two-Higgs-doublet model in the inverted Higgs scenario can retain the theoretical stability all the way up to the Planck scale. The Planck-cutoff scale, $\Lambda_{\rm cut}^{\rm Planck}$, directly impacts the mass spectra such that all the extra Higgs boson masses should be light below about 160 GeV. However, the observation of the light masses of new Higgs bosons does not indicate the high cutoff scale because a low cutoff scale can also accommodate the light masses. Over the viable parameter points that satisfy the theoretical requirements and the experimental constraints, we show that the trilinear Higgs couplings for low $\Lambda_{\rm cut}$ are entirely different from those for the Planck-cutoff scale. The most sensitive coupling to the cutoff scale is from the $h$-$h$-$h$ vertex, where $h$ is the lighter CP-even Higgs boson at a mass below 125 GeV. Among the multi-Higgs productions mediated by Higgs bosons, the gluon fusion processes of $gg \to h h $ and $gg \to AA$ are insensitive to the cutoff scale, yielding a small variation of $\mathcal{O}(1)\,{\rm fb}$ according to $\Lambda_{\rm cut}$. The smoking-gun signature is from the triple Higgs production of $q\bar{q}' \to W^* \to H^\pm hh$, which solely depends on the $h$-$h$-$h$ vertex. The cross section for $\Lambda_{\rm cut}=1\,{\rm TeV}$ is about $10^3$ times larger than that for the Planck-cutoff scale. Since the decay modes of $H^\pm \to W^* h/W^* A$ and $h/A \to bb$ are dominant, the process yields the $6b+\ell\nu$ final state, which enjoys an almost background-free environment. Consequently, the precision measurement of $pp \to H^\pm hh$ can probe the cutoff scale of the model.

Vacuum stability of the type II seesaw leptogenesis from inflation

Recently, it has been found that introducing a triplet Higgs to the standard model could provide a feasible leptogenesis to generate the baryon asymmetry of our Universe, providing that the inflation is driven by the mixing state of the triplet Higgs and standard model Higgs. In this work, we survey the viable parameter space satisfying the vacuum stability and perturbativity in this model. We find that the introduction of the triplet Higgs would also ameliorate the problem of the Higgs vacuum instability. We present two representative parameter regions where the origin of neutrino masses, baryon asymmetry of the Universe, and inflation can be explained while keeping consistent with the condition of vacuum stability and perturbativity.

Resonant search for the X17 boson at PADME

We discuss the experimental reach of the Frascati PADME experiment in searching for new light bosons via their resonant production in positron annihilation on fixed target atomic electrons. A scan in the mass range around 17 MeV will thoroughly probe the particle physics interpretation of the anomaly observed by the ATOMKI nuclear physics experiment. In particular, for the case of a spin-1 boson, the viable parameter space can be fully covered in a few months of data taking.

Tests of low-scale leptogenesis in charged lepton flavour violation experiments

We consider low-energy tests of low-scale leptogenesis based on the type I seesaw scenario with three right-handed singlet neutrinos νlR. In this scenario, successful leptogenesis is possible for quasi-degenerate in mass heavy Majorana neutrinos N1,2,3, M1,2,3≅M, |Mj−Mi|≪M, i≠j=1,2,3, heavy Majorana neutrino masses M∼(0.05−5×105) GeV, and Nj charged current and neutral current weak interaction couplings as large as O(10−2). We derive the constraints on the corresponding leptogenesis parameter space from the existing data from low-energy experiments, including the limits from the experiments on μ→eγ decay and on the rate of μ−e conversion in gold. We show also that the planned and upcoming experiments on charged lepton flavour violation with μ±, MEG II on the μ→eγ decay, Mu3e on μ→eee decay, Mu2e and COMET on μ−e conversion in aluminium and PRISM/PRIME on μ−e conversion in titanium, can probe significant region of the viable leptogenesis parameter space, and thus have a potential for a discovery. Experiments on τ→eee(μμμ) and τ→e(μ)γ decays (e.g., BELLE II) also can probe a part of the leptogenesis parameter space, although a relatively small one.

Thermal Leptophilic Light Vector Dark Matter with Spinor Mediator and Muon (g-2) Anomaly

Inspired by the recently new measurement of (g − 2)μ at FermiLab and reported upper bound for electron-dark matter (DM) recoil by the XENON1T collaboration, we revisited phenomenology of a light MeV scale vector dark matter in a leptophilic extension of standard model while a new spinor field plays the role of mediator. A viable parameter space is considered to discuss the possibility of light dark matter relic density as well as anomalous magnetic moment of the muon. We study DM-electron direct detection and cosmological bounds on the parameters space of the model. It is shown that although new bound of (g − 2)μ anomaly greatly confines the parametric space of the model, the thermal light dark matter can exist for \(\mathrm {M_{DM}} \sim 10^{-1}-10^{1} \text {GeV}\).

Core-collapse supernova constraint on the origin of sterile neutrino dark matter via neutrino self-interactions

Novel neutrino self-interaction can open up viable parameter space for the relic abundance of sterile-neutrino dark matter (SνDM). In this work, we constrain the relic target using core-collapse supernova which features the same fundamental process and a similar environment to the early universe era when SνDM is dominantly produced. We present a detailed calculation of the effects of a massive scalar mediated neutrino self-interaction on the supernova cooling rate, including the derivation of the thermal potential in the presence of non-zero chemical potentials from plasma species. Our results demonstrate that the supernova cooling argument can cover the neutrino self-interaction parameter space that complements terrestrial and cosmological probes.

New pathways to the relic abundance of vector-portal dark matter

We fully explore the thermal freezeout histories of a vector-portal dark matter model, in the region of parameter space in which the ratio of masses of the dark photon $A^{\prime}$ and dark matter $\chi$ is in the range $1 \lesssim m_{A^{\prime}}/m_{\chi} \lesssim 2$. In this region $2 \rightarrow 2$ and $3 \rightarrow 2$ annihilation processes within the dark sector, as well as processes that transfer energy between the dark sector and the Standard Model, play important roles in controlling the thermal freezeout of the dark matter. We carefully track the temperatures of all species, relaxing the assumption of previous studies that the dark and Standard Model sectors remain in thermal equilibrium throughout dark matter freezeout. Our calculations reveal a rich set of novel pathways which lead to the observed relic density of dark matter, and we develop a simple analytic understanding of these different regimes. The viable parameter space in our model provides a target for future experiments searching for light (MeV-GeV) dark matter, and includes regions where the dark matter self-interaction cross section is large enough to affect the small-scale structure of galaxies.

Axiogenesis with a heavy QCD axion

We demonstrate that the observed cosmological excess of matter over anti-matter may originate from a heavy QCD axion that solves the strong CP problem but has a mass much larger than that given by the Standard Model QCD strong dynamics. We investigate a rotation of the heavy QCD axion in field space, which is transferred into a baryon asymmetry through weak and strong sphaleron processes. This provides a strong cosmological motivation for heavy QCD axions, which are of high experimental interest. The viable parameter space has an axion mass ma between 1 MeV and 10 GeV and a decay constant fa< 105 GeV, which can be probed by accelerator-based direct axion searches and observations of the cosmic microwave background.

Improved white dwarves constraints on inelastic dark matter and left-right symmetric models

WIMPs can be captured in compact stars such as white dwarves (WDs) leading to an increase in the star luminosity through their annihilation process. We show that when the WIMP interacts with the nuclear targets within the WD through inelastic scattering and its mass exceeds a few tens GeV the data on low-temperature large-mass WDs in the Messier 4 globular cluster can probe values of the mass splitting $\delta\lesssim$ 40 MeV. Such value largely exceeds those ensuing from direct detection and from solar neutrino searches. We apply such improved constraint to the specific DM scenario of a self-conjugate bi-doublet in the Left-Right Symmetric Model (LRSM), where the standard $SU(2)_L$ group with coupling $g_L$ is extended by an additional $SU(2)_R$ with coupling $g_R$. We show that bounds from WDs significantly reduce the cosmologically viable parameter space of such scenario, in particular requiring $g_R>g_L$. For instance, for $g_R/g_L$ = 1.8 we find the two viable mass ranges 1.2 TeV $\lesssim m_\chi\lesssim$ 3 TeV and 5 TeV $\lesssim m_\chi\lesssim$ 10 TeV, when the charged $SU(2)_R$ gauge boson mass $M_{W_2}$ is lighter than $\simeq$ 12 TeV. We also discuss the ultraviolet completion of the LRSM model, when the latter is embedded in a Grand Unified Theory. We show that such low-energy parameter space and compatibility to proton-decay bounds require a non-trivial extension of the particle content of the minimal model. We provide a specific example where $M_{W_2}\lesssim$ 10 TeV is achieved by extending the LRSM at high energy with color triplets that are singlets under all other groups, and $g_R/g_L>$1 is obtained by introducing $SU(2)_L$ triplets with no $SU(2)_R$ counterparts, i.e. by breaking the symmetry between the multiplets of $SU(2)_L$ and $SU(2)_R$.

Generic U(1)X models inspired from SO(10)

We propose the family universal $U(1)_X$ models with three right-handed neutrinos by choosing the $U(1)_X$ gauge symmetry as a linear combination of $U(1)_Y\times U(1)_{\chi}$ of $SO(10)$. To be consistent with the quantum gravity effects, we introduced a Dirac fermion $\chi$ as a dark matter candidate, which is odd under the gauged $Z_2$ symmetry after $U(1)_X$ breaking. The isospin violation dark matter with $f_n/f_p = -0.7$ can be realized naturally, and thus the LUX, PANDAX, and XENON1T experimental constraints can be evaded. Moreover, we study the masses and mixings for Higgs and gauge bosons, consider the LHC constraints on the $Z'$ mass, simulate various constraints from dark matter direct and indirect detection experiments, and then present the viable parameter spaces. To study the LHC $Z'$ mass bounds on the generic $U(1)_X$ models, we considered four kinds of scenarios, where scenario II with zero $U(1)_X$ charge for right-handed up-type quarks can relax the LHC $Z'$ mass bound a little bit.

Investment in Mobility by Car as an Explanatory Variable for Market Segmentation

According to the traditional approach, when estimating changes in transportation policies, the household income level (in all its forms) is perceived as the proper explanatory variable for modeling population transportation preferences. However, it is acknowledged that accurate information about this variable is difficult to gather. In contrast, information about household car characteristics is relatively simple to collect. This article presents the hypothesis that a lifestyle variable, such as investment in mobility by car (IMC), is a viable parameter for estimating household members’ behavioral tendencies toward transportation, from both practical and conceptual reasons.This research proposes a simple methodology to infer the IMC using existing data sources, and presents mode choice model estimation results using the IMC both as an explanatory variable and as a segmentation variable. The segmentation of the population in three IMC categories (low, middle, and high) yielded significantly different models of the preference systems for the three segments. These findings show that IMC is a viable variable for market segmentation.

CMB constraints on DHOST theories

We put constraints on the degenerate higher-order scalar-tensor (DHOST) theories using the Planck 2018 likelihoods. In our previous paper, we developed a Boltzmann solver incorporating the effective field theory parameterised by the six time-dependent functions, αi (i = B, K, T, M, H) and β 1, which can describe the DHOST theories. Using the Markov-Chain Monte-Carlo method with our Boltzmann solver, we find the viable parameter region of the model parameters characterising the DHOST theories and the other standard cosmological parameters. First, we consider a simple model with α = ΩDE(t)/ΩDE(t 0), α B = α T = α M = α H = 0 and β 1 = β 1,0ΩDE(t)/ΩDE(t 0) in the ΛCDM background where t 0 is the present time and obtain β 1,0 = 0.032-0.016 +0.013 (68% c.l.). Next, we focus on another theory given by ℒDHOST = X + c 3 X□ϕ/Λ3 + (M pl 2/2 + c 4 x 2/Λ6)R + 48c 4 2 X 2/ (M pl 2Λ12 + 2c 4Λ6 X 2)ϕμ ϕμρ ϕρν ϕν with X := ∂μϕ∂μϕ and two positive constant parameters, c 3 and c 4. In this model, we consistently treat the background and the perturbations, and obtain c 3 = 1.59+0.26 -0.28 and the upper bound on c 4, c 4 < 0.0088 (68% c.l.).

Hierarchy problem and the vacuum stability in two-scalar dark matter model

We consider an extension to the Standard Model (SM) with two extra real singlet scalars which interact with the SM Higgs particle. The lighter scalar is taken as the dark matter (DM) candidate. We show that the model successfully explains the relic abundance of the DM in the universe and evades the strong bounds from direct detection experiments while respecting the perturbativity and the vacuum stability conditions. In addition, we study the hierarchy problem within the Veltman approach by solving the renormalization group equations at one-loop. We demonstrate that the addition of the real singlet scalars contributes to the Veltman parameters which in turn results in satisfying the Veltman conditions much lower than the Planck scale $ \Lambda_\text{Pl}$ down to the electroweak scale. Therefore, the presence of the extra scalars solves the fine-tuning problem of the Higgs mass. For the case of the two-scalar DM model we find two representative points in the viable parameter space which satisfy also the Veltman conditions at $\Lambda = 300$ GeV and $\Lambda = 1$ TeV.

Radiative plateau inflation with conformal invariance: Dynamical generation of electroweak and seesaw scales

We investigate a scale-invariant $B-L$ scenario where the Standard Model (SM) is supplemented with a dark scalar $\phi$ which has gauge \& Yukawa interactions, with the couplings $g_{BL}$ and $y$, respectively, leading to radiative plateau inflation at scale $\phi=M$ in the ultraviolet (UV), while dynamically generating the Electroweak and Seesaw scales \textit{\'a l\'a} Coleman-Weinberg in the infrared (IR). This is particularly achieved by implementing threshold corrections at an energy scale $\mu_T$ arising due to the presence of vector-like fermions. We show that implementing the inflationary observables makes the couplings solely dependent on the plateau scale $M$, leaving us with only two independent parameters $M$ and $\mu_T$. Within the theoretically consistent parameter space defined by $m_{Z_{BL}} > 850~\rm GeV$, from the assumption of independent evolution of the dark sector couplings from the SM couplings and $M < 5.67~M_P$ required for the realisation of inflationary \textit{plateau-like} behaviour of the potential around $\phi=M$, where $M_P=2.4\times10^{18}$ GeV is the reduced Planck mass, we identify the parameter space that is excluded by the current LHC results from the search for the heavy $Z_{BL}$ boson. For typical benchmark points in the viable parameter regions, we estimate the reheating temperature to be $\mathcal{O}(TeV)$ thus consistent with the standard Big Bang Nucleosynthesis (BBN) constraints. For typical benchmark points ($M=5.67,~1,~0.1~M_P$) we predict the scales of inflation to be $\mathcal{H}_{inf}=2.79\times10^{12}$ GeV, $1.53\times10^{10}$ GeV and $1.53\times10^7$ GeV, respectively.

Gravitational wave and CMB probes of axion kination

Rotations of an axion field in field space provide a natural origin for an era of kination domination, where the energy density is dominated by the kinetic term of the axion field, preceded by an early era of matter domination. Remarkably, no entropy is produced at the end of matter domination and hence these eras of matter and kination domination may occur even after Big Bang Nucleosynthesis. We derive constraints on these eras from both the cosmic microwave background and Big Bang Nucleosynthesis. We investigate how this cosmological scenario affects the spectrum of possible primordial gravitational waves and find that the spectrum features a triangular peak. We discuss how future observations of gravitational waves can probe the viable parameter space, including regions that produce axion dark matter by the kinetic misalignment mechanism or the baryon asymmetry by axiogenesis. For QCD axion dark matter produced by the kinetic misalignment mechanism, a modification to the inflationary gravitational wave spectrum occurs above 0.01 Hz and, for high values of the energy scale of inflation, the prospects for discovery are good. We briefly comment on implications for structure formation of the universe.

Linear sigma dark matter

We present a model of self-interacting dark matter based on QCD-like theories and inspired by the proximity of a0(980 ± 20) to the Koverline{K} (990) threshold. Dark matter is comprised of dark pions which self-scatter via the σ resonance close to the ππ threshold. While the linear sigma model serves as a qualitative guide, a fully unitary description of the scattering in the strongly coupled regime is given by effective range theory. The introduction of a kinetically mixed dark photon allows the dark pion to either freeze-out or -in. We study the viable parameter space which explains the observed relic abundance while evading all current constraints. Searches for dark matter self interactions at different scales, (in)direct detection signals, and (in)visibly-decaying dark photons will test this model in the near future.