Neutral Scalar Particle Research Articles

Preliminary analyses of the dynamics and thermodynamics of rotating regular black holes* *Supported in part by the National Natural Science Foundation of China (12175108)

We investigate the dynamic and thermodynamic laws governing rotating regular black holes. By analyzing dynamic properties, i.e., the interaction between scalar particles and rotating regular black holes, we establish the criteria that determine whether such black holes satisfy the laws of thermodynamics. In addition, we provide the general form of conserved quantities related to rotating regular black holes, including the relevant flows associated with neutral scalar particles. Meanwhile, we reexamine the relationship between the third law of thermodynamics and weak cosmic censorship conjecture for rotating regular black holes. Based on the abovementioned criteria, we discuss the laws of thermodynamics for three models of rotating regular black holes: Rotating Hayward black holes, Kerr black-bounce solutions, and loop quantum gravity black holes. Our findings indicate that none of the three models satisfies the first law of thermodynamics. In particular, the first and third models fail to comply with the three laws of thermodynamics, whereas the second model satisfies only the second and third laws of thermodynamics. Finally, we attempt to rescue the laws of thermodynamics by modifying entropy or extending the phase space. However, the two scenarios cannot ensure the three laws of thermodynamics in the three models, which reveals an unusual property of rotating regular black holes.

Muon g−2 and a type-X two-Higgs-doublet scenario: Some studies in high-scale validity

We study the high-scale validity of a Type-X two Higgs doublet scenario which provides an explanation of the observed value of muon $(g-2)$. This region admits of a pseudoscalar physical state, which is well below the observed 125-GeV scalar in mass. A second neutral scalar particle can be both above and below 125 GeV in such a scenario. Admissible regions in the parameter space are obtained by using the most recent data on muon $(g-2)$, theoretical constraints such as low-scale perturbativity and vacuum stability, and also all experimental constraints, including the available LHC results. Among other things, both the aforesaid orders of CP-even neutral scalar masses are included in our benchmark studies. Two-loop renormalisation group equations are used to predict the values of various couplings at high scales, and the regions in the space spanned by low-scale parameters, which retain perturbative unitarity as well as vacuum stability upto various scales are identified. We thus conclude that such a scenario, while successfully explaining the observed muon $(g-2)$, can be valid upto energy scales ranging from $10^{4}$ GeV to the Planck scale, thus opening up directions of thought on its ultraviolet completion.

General one-loop formulas for Hrightarrow fbar{f}gamma and its applications

General one-loop contributions to the decay processes Hrightarrow fbar{f}gamma and its applications are presented in this paper. We consider all possible contributions of the additional heavy vector gauge bosons, heavy fermions, and charged (also neutral) scalar particles propagating in Feynman loop diagrams. Therefore, analytic results are valid in a wide class of models beyond the Standard Model. Analytic formulas for the form factors are expressed in terms of Passarino-Veltman functions in the standard notations of LoopTools. Hence, the decay rates can be evaluated numerically by using this package. The computations are then applied to the cases of the Standard Model, U(1)_{B-L} extension of the Standard Model as well as Two Higgs Doublet Model. Phenomenological results for all the above models are studied. We observe that the effects of new physics are sizable contributions and these can be probed at future colliders.

Spontaneous magnetization and electroweak phase transition in the scalar sector of 2HDM

We discuss theoretical and phenomenological aspects of the two­-Higgs­-doublet extensions of the Standard model. In modern notation the h2HDM is the model with mh = 125.26 GeV, where the lightest neutral scalar particle in 2HDM is the usual Higgs boson in Standard Model.
 The parametric space of this model is very rich and admits many scenarios of New Physics’ phenomenol­ogy.The many restrictions and conditions should be satisfied. One of them is the Sakharov’s conditions for the formation of the baryon asymmetry of the Universe in models with extra scalar fields. We try to show that we can satisfy them in the h2HDM and find the region of parametric space where the electroweak phase transition is first order. The Sakharov’s conditions are not satisfied in Standard Model but it is fundamental problem of modeling the Universe, so the searching of New physics this way is relevant.

General one-loop contributions to the decay $H\rightarrow \nu_l\bar{\nu}_l\gamma$

Abstract General one-loop contributions to the decay amplitudes $H\rightarrow \nu_l\bar{\nu}_l\gamma$ are presented, considering all possible contributions of additional heavy vector gauge bosons, fermions, and charged (and also neutral) scalar particles appearing in the loop diagrams. Moreover, the results can be applied directly when extra neutrinos (apart from three ones in the standard model) are taken into account in final states. Analytic results are expressed in terms of Passarino–Veltman scalar functions which can be evaluated numerically using $\texttt{LoopTools}$. In the standard model framework, these analytical results are generated and cross-checked with previous computations. We find that our results are well consistent with these computations. Within the standard model limit, phenomenological results for the decay channels are also studied using the present input parameters at the Large Hadron Collider. Lastly, the calculation is also applied to the Two Higgs Doublet Model framework as another example.

One-loop corrections to the [formula omitted] vertex in models with scalar doublets and singlets

We study the one-loop corrections to the Zbb¯ vertex in extensions of the Standard Model with arbitrary numbers of scalar doublets, neutral scalar singlets, and charged scalar singlets. Starting with a general parameterization of theories with neutral and singly-charged scalar particles, we derive the conditions that, in a renormalizable model, must be obeyed by the couplings in order for the divergent contributions to cancel. Then, we show that those conditions are indeed obeyed by the models that we are interested in, and we write down the full finite expression for the vertex in those models. We apply our results to some particular cases, highlighting the importance of the diagrams with neutral scalars.

Gravitational wave stochastic background from cosmological particle decay

We assume that the cosmological dark matter is composed of massive neutral scalar particles that decay into two massless particles. The decay produces a stochastic background of gravitational waves (GWs) via a 'memory effect' mechanism. We calculate the spectral amplitude and slope of the resulting background, which is frequency independent (flat). We discuss its potential observability and show that the resulting background might dominate the cosmological GW background at frequencies above about 10 GHz. Penrose has proposed a cosmological model in which dark matter particles have the Planck mass and decay into two gravitons. For these, the spectrum has an additional 'direct' contribution from the decay products, which we also calculate. At low frequencies, this direct contribution also has a flat spectrum but with a much smaller amplitude than the memory part.

Prospects for heavy scalar searches at the LHeC

In this paper, we study the prospects of the proposed Large Hadron electron Collider (LHeC) in the search for heavy neutral scalar particles. We consider a minimal model with one additional complex scalar singlet that interacts with the Standard Model (SM) via mixing with the Higgs doublet, giving rise to an SM-like Higgs boson [Formula: see text] and a heavy scalar particle [Formula: see text]. Both scalar particles are produced via vector boson fusion and can be tested via their decays into pairs of SM particles, analogously to the SM Higgs boson. Using multivariate techniques, we show that the LHeC is sensitive to [Formula: see text] with masses between 200 and 800 GeV down to scalar mixing of [Formula: see text].

Magnetic field effect on the decay process of a neutral scalar boson to charged fermions

The effect of a homogeneous weak magnetic field on the decay process of a neutral scalar particle to a pair of charged fermions is studied. The decay rate is calculated through the imaginary part of the self‐energy of the scalar particle interacting with the charged fermions, at one loop. The weak field approximation can be performed in different ways, depending on the hierarchy of scales. Here, we explore the regime where the progenitor particle has a high transverse momentum and we find that the process is favored by the increase of the magnetic field. We compare our results with recent findings for a different kinematical regime and briefly discuss the possible physical reasons for the different behaviors. The phenomenon can be relevant in early universe events or in high‐energy collisions.

Effect of the magnetized medium on the decay of neutral scalar bosons

The decay of a heavy neutral scalar particle into fermions and into charged scalars are analyzed when in the presence of an external magnetic field and finite temperature. Working in the one-loop approximation for the study of these decay channels, it is shown that the magnetic field leads in general to a suppression of the decay width whenever the kinematic constrain depends explicitly on the magnetic field. Our results are also compared with common approximations found in the literature, e.g., when the magnitude of the external magnetic field is smaller than the decaying product particle masses, i.e., in the weak field approximation, and in the opposite case, i.e., in the strong field approximation. Possible applications of our results are discussed.

Search for a lighter Higgs boson in the Next-to-Minimal Supersymmetric Standard Model**Supported by National Natural Science Foundation of China (11505208, 11661141007, 11705016, 11875275), China Ministry of Science and Technology (2018YFA0403901) and partially by the France China Particle Physics Laboratory (FCPPL) and CAS Center for Excellence in Particle Physics (CCEPP)

Following the discovery of the Higgs boson with a mass of approximately 125 GeV at the LHC, many studies have been performed from both the theoretical and experimental viewpoints to search for a new Higgs Boson that is lighter than 125 GeV. We explore the possibility of constraining a lighter neutral scalar Higgs boson h1 and a lighter pseudo-scalar Higgs boson a1 in the Next-to-Minimal Supersymmetric Standard Model by restricting the next-to-lightest scalar Higgs boson h2 to be the one observed at the LHC after applying the phenomenological constraints and those from experimental measurements. Such lighter particles are not yet completely excluded by the latest results of the search for a lighter Higgs boson in the diphoton decay channel from LHC data. Our results show that some new constraints on the Next-to-Minimal Supersymmetric Standard Model could be obtained for a lighter scalar Higgs boson at the LHC if such a search is performed by experimental collaborations and more data. The potentials of discovery for other interesting decay channels of such a lighter neutral scalar or pseudo-scalar particle are also discussed.

Towards a viable scalar interpretation of RD(*)

Recent measurements of semileptonic B-meson decays seemingly imply violations of lepton flavor universality beyond the Standard Model predictions. With three-level explanations based on extended Higgs sectors being strongly challenged by the measurements of the $B_c^-$ lifetime, new theories invoking leptoquark or vector fields appear as the only feasible answer. However, in this work we show that simple scalar extensions of the Standard Model still offer a possible solution to the $B$ physics puzzle, owing to sizeable loop-level corrections which mimic the effects of new vector contributions. Considering a simplified model characterised by a charged and a neutral scalar particle, we verify the compatibility of the observed $R_{D^{(*)}}$ signal with the relevant collider bounds. We also study an embedding of the simplified model into a three-Higgs-doublet framework, and investigate its main phenomenological constraints.

Semialigned two Higgs doublet model

In the left-right symmetric model based on $SU(2)_L\times SU(2)_R\times U(1)_{B-L}$ gauge symmetry, there appear heavy neutral scalar particles mediating quark flavor changing neutral currents (FCNCs) at tree level. We consider a situation where such FCNCs give the only sign of the left-right model while $W_R$ gauge boson is decoupled, and name it "semi-aligned two Higgs doublet model" because the model resembles a two Higgs doublet model with mildly-aligned Yukawa couplings to quarks. We predict a correlation among processes induced by quark FCNCs in the model, and argue that future precise calculation of meson-antimeson mixings and CP violation therein may hint at the semi-aligned two Higgs doublet model and the left-right model behind it.

Topological Aharonov-Bohm Effect of Neutral Scalar Particle on Noncommutative Space

We study the interactions between a neutral scalar particle and electromagnetic fields on noncommutative space. Because of the noncommutativity of space, neutral particle can couple to electromagnetic fields at the tree level, and the interaction strength is represented by a new coupling constant. We find that on noncommtuative space the topological Aharonov-Bohm effect is nontrivial even for neutral scalar particle.

Bounds for lighter Higgses in extensions of the Standard Model

Higgs bosons lighter than the 125 GeV one can be present in extensions of the Standard Model and exclusion or discovery of such a possibility allows to improve our knowledge of the Higgs sector. I consider Two Higgs Doublet Models, which are the minimal scalar structure of a large number of models, in order to explore the possibility of constraining a neutral scalar particle lighter than the 125 GeV Higgs boson. Such a lighter particle is not yet completely excluded by present data. I show that some new constraints can be obtained at the LHC for these light particles.

Search for a lighter Higgs boson in Two Higgs Doublet Models

We consider present constraints on Two Higgs Doublet Models, both from the LHC at Run 1 and from other sources in order to explore the possibility of constraining a neutral scalar or pseudo-scalar particle lighter than the 125 GeV Higgs boson. Such a lighter particle is not yet completely excluded by present data. We show with a simplified analysis that some new constraints could be obtained at the LHC if such a search is performed by the experimental collaborations, which we therefore encourage to continue carrying out light diphoton resonance searches at $\sqrt{s}=$ 13 TeV in the context of Two Higgs Doublet Models.

Cosmological particle decays at finite temperature

We calculate finite-temperature corrections to the decay rate of a generic neutral (pseudo)scalar particle that decays into (pseudo)scalars or fermion-antifermion pairs. The ratio of the finite-temperature decay rate to the zero-temperature decay rate is presented. Thermal effects are largest in the limit where the decaying particle is nonrelativistic but with a mass well below the background temperature, but significant effects are possible even when we relax the former assumption. Thermal effects are reduced for the case of nonzero momentum of the decaying particle. We discuss cosmological scenarios under which significant finite-temperature corrections to the decay rate can be achieved.

Search for long-lived neutral particles decaying to quark-antiquark pairs in proton-proton collisions ats=8 TeV

A search is performed for long-lived massive neutral particles decaying to quark-antiquark pairs. The experimental signature is a distinctive topology of a pair of jets, originating at a secondary vertex. Events were collected with the CMS detector at the CERN LHC in proton-proton collisions at a centre-of-mass energy of 8 TeV. The data analyzed correspond to an integrated luminosity of 18.5 inverse femtobarns. No significant excess is observed above standard model expectations. Upper limits at 95% confidence level are set on the production cross section of a heavy neutral scalar particle, H, in the mass range of 200 to 1000 GeV, decaying promptly into a pair of long-lived neutral X particles in the mass range of 50 to 350 GeV, each in turn decaying into a quark-antiquark pair. For X with mean proper decay lengths of 0.4 to 200 cm, the upper limits are typically 0.5-200 fb. The results are also interpreted in the context of an R-parity-violating supersymmetric model with long-lived neutralinos decaying into a quark-antiquark pair and a muon. For pair production of squarks that promptly decay to neutralinos with mean proper decay lengths of 2-40 cm, the upper limits on the cross section are typically 0.5-3 fb. The above limits are the most stringent on these channels to date.

Gravitational corrections to the scattering of scalar particles

We evaluated the scattering amplitude of neutral scalar particles at one-loop order in the context of effective field theory of quantum gravity in the presence of a cosmological constant. Our study suggests that quantum gravitational corrections induce an asymptotic freedom behavior to the $\lambda\phi^4$ theory, for a positive cosmological constant. This result hints that a complete theory of quantum gravity can play an important role to avoid the issue of triviality in quantum field theory.

Milli-interacting dark matter

We present a dark matter model reproducing well the results from DAMA/LIBRA and CoGeNT and having no contradiction with the negative results from XENON100 and CDMS-II/Ge. Two new species of fermions F and G form hydrogen-like atoms with standard atomic size through a dark U(1) gauge interaction carried out by a dark massless photon. A Yukawa coupling between the nuclei F and neutral scalar particles S induces an attractive shorter-range interaction. This dark sector interacts with our standard particles because of the presence of two mixings, a kinetic photon-dark photon mixing, and a mass {\sigma}-S mixing. The dark atoms from the halo diffuse elastically in terrestrial matter until they thermalize and then reach underground detectors with thermal energies, where they form bound states with nuclei by radiative capture. This causes the emission of photons that produce the signals observed by direct-search experiments.