Scalar Particles Research Articles

Near-extremal charged black holes: greybody factors and evolution

As a charged black hole reaches its extremal state via Hawking radiation, quantum effects become important for its thermodynamic properties when its temperature is below a mass gap scale. Using AdS2/CFT1 correspondence and solutions for the corresponding Schwarzian action, we calculate the black hole greybody factors including the quantum effects. In the low temperature limit, the greybody factors scale as T2s+3/2 with s the radiated field spin. Hence, the Hawking radiation of a near-extremal charged black hole (NEBH) is dominated by emitting scalar particles including the Higgs boson. Time evolution of an NEBH is also calculated and shows a stochastic feature. For an NEBH lighter than around 108 times the Planck mass, its temperature at the current universe is below the mass gap scale and is universally tens of GeV, which is important if one searches for primordial (hidden) charged black holes.

Effects of nontrivial topology with Coulomb-types scalar and vector potential on relativistic quantum motions of scalar charged bosons

In this paper, we study the relativistic quantum motions of spin-zero scalar bosons confined by the quantum flux field in the presence of Coulomb-type scalar potential in the background of a topologically nontrivial 4D space–time. Afterwards, we introduce a Coulomb-like vector potential through a minimal substitution in the wave equation and determine the eigenvalue solutions of the quantum system analytically. In fact, it is shown there that the nontrivial topology of the geometry, Coulomb-types scalar and vector potential, and the quantum flux field influence the energy profile and wave function of the scalar bosons and get them modified. Also, the gravitational analogue of the Aharonov–Bohm effect is observed because the energy eigenvalue depends on the geometric quantum phase.

Composite scalar boson mass dependence on the constituent mass anomalous dimension

We perform a Bethe–Salpeter equation (BSE) evaluation of composite scalar boson masses in order to verify how these masses can be smaller than the composition scale. The calculation is developed with a constituent self-energy dependent on its mass anomalous dimension ([Formula: see text]), and we obtain a relation showing how the scalar mass decreases as [Formula: see text] is increased. We also discuss how fermionic corrections to the BSE kernel shall decrease the scalar mass, whose effect can be as important as the one of a large [Formula: see text]. An estimate of the top quark loop effect that must appear in the BSE calculation gives a lower bound on the composite scalar mass.

Phase Structure of Electroweak Vacuum in a Strong Magnetic Field: The Lattice Results.

Using first-principle lattice simulations, we demonstrate that in the background of a strong magnetic field (around 10^{20} T), the electroweak sector of the vacuum experiences two consecutive crossover transitions associated with dramatic changes in the zero-temperature dynamics of the vector W bosons and the scalar Higgs particles, respectively. Above the first crossover, we observe the appearance of large, inhomogeneous structures consistent with a classical picture of the formation of W and Z condensates pierced by vortices. The presence of the W and Z condensates supports the emergence of the exotic superconducting and superfluid properties induced by a strong magnetic field in the vacuum. We find evidence that the vortices form a disordered solid or a liquid rather than a crystal. The second transition restores the electroweak symmetry. Such conditions can be realized in the near-horizon region of the magnetized black holes.

Two-Dimensional Symmetry Breaking at the Event Horizon of Black Holes

This work investigates the combined dynamics of the Yang–Mills and Liouville gravity fields at the event horizon of black holes. To analyze quantum dynamics at the event horizon of black holes existing in a three-dimensional (spatial) universe, a two-dimensional formulation is introduced. The following hypothesis is proposed in this work: there exists a two-dimensional analogue to the Higgs field at the event horizon. This field is then considered as a two-dimensional Yang–Mills field. The interaction and symmetry breaking of the combined two-dimensional Yang–Mills and Liouville gravitational fields are then discussed. The resulting gravitational scalar boson and its implications to the quantum dynamics occurring at the event horizon are presented.

Depleted Higgs boson: Searches for universal coupling suppression, invisible decays, and mixed-in scalars

Two simple ways by which the standard signals of the Standard Model Higgs boson can be depleted are: its couplings to fermions and gauge bosons can be suppressed by a universal factor, and part of its branching fraction can be drained into invisible final states. A large class of theories can impose one or both of these depletion factors, even if mild, by way of additional scalar bosons that are singlets under the Standard Model but mix with the Higgs boson. We perform a comprehensive survey of the present status of the depleted Higgs boson, and discuss future prospects for detecting the presence of either depletion factor. We also survey the constraints status and future detection prospects for the generic case of extra mixed-in scalars which generically lead to these depletion factors for the Higgs boson. We find, for example, that precision study of the Higgs boson in many cases is more powerful than searches for the extra scalar states, given the slate of next-generation experiments that are on the horizon.

Evaporation of a Kerr-black-bounce by emission of scalar particles

We study a regular rotating black hole evaporating under the Hawking emission of a single scalar field. The black hole is described by the Kerr-black-bounce metric with a nearly extremal regularizing parameter $\ell=0.99r_+$. We compare the results with a Kerr black hole evaporating under the same conditions. Firstly, we compute the gray-body factors and show that the Kerr-black-bounce evolves towards a non-Schwartzchild-like asymptotic state with $a_* \sim 0.47$, differently from a Kerr black hole whose asymptotic spin would be $a_* \sim 0.555$. We show that this result depends on the combined contributions of the differences in the gray-body factors and the surface gravity affected by the regularizing parameter. We also discuss how the surface gravity affects the temperature and the primary emissivity and decreases those quantities with respect to the Kerr black hole. Consequently, the regular black hole has a longer lifetime. Finally, we briefly comment on the possibility of investigating the beyond-the-horizon structure of a black hole exploiting its Hawking emission.

Some remarks on scalar particles under the influence of noninertial effects in a spacetime with a screw dislocation

Some remarks on scalar particles under the influence of noninertial effects in a spacetime with a screw dislocation

Gravitational Coleman-Weinberg mechanism

The Coleman-Weinberg mechanism provides a procedure by which a scalar field, which initially has no mass parameters, acquires a mass due to the anomalous nature of scale symmetry. Loop corrections trigger a spontaneous symmetry breaking and the appearance of a non-trivial vacuum. We first review the basic example of the Coleman-Weinberg mechanism, scalar Quantum Electrodynamics, in a perturbative regime where the scalar particle becomes massive through photon loops. We then present the main results of this article, what we name the gravitational Coleman-Weinberg mechanism: we analyse the same effect in a gravitational theory without explicit energy scales at tree-level. Finally, we also study the mechanism for two scalar fields in the mentioned gravitational theory. We will derive the gravitational Coleman-Weinberg potentials, analyse the parameter space where we have a symmetry breaking, and obtain the value of the corresponding scalar masses.

Dineutron decay into sterile antineutrinos in neutron stars and its observable consequences

In some extensions of the Standard Model (SM), two neutrons are allowed to decay into two sterile antineutrinos ($nn\ensuremath{\rightarrow}\overline{\ensuremath{\chi}}\overline{\ensuremath{\chi}}$) via new scalar bosons. This process violates both the baryon number ($\mathcal{B}$) and the lepton number ($\mathcal{L}$) by two units but conserves their difference $(\mathcal{B}\ensuremath{-}\mathcal{L})$. Neutron stars contain a large number of neutrons, and thus the $nn\ensuremath{\rightarrow}\overline{\ensuremath{\chi}}\overline{\ensuremath{\chi}}$ process can be greatly enhanced inside a neutron star. This process could result in nontrivial effects that are different from the SM predictions and can be explored through astrophysical and laboratory observations. Furthermore, a large number of sterile antineutrinos, which may be dark matter candidates, can be emitted from the interior of the neutron star. The properties of the emitted particles show a particular pattern that can be uniquely determined by the mass and radius of the neutron star. In addition, the dineutron decay may contribute to the orbital-period change of the binary systems containing neutron stars. We analyze the possibility of constraining the mass of the new scalar bosons using the observations of the binary's orbital-period changes. It is found that the mass of the new scalar bosons is roughly restricted in the range from 1 TeV to several TeV, which is possibly within the reach of direct searches at the LHC or future high-energy experiments. The joint analysis which combines the astrophysics and particle phenomenology could provide an excellent opportunity for the study of the new physical effects beyond the SM.

Spin dynamics in nonuniform electromagnetic wave fields

Based on solution of Dirac equation, the dynamics of a quantum particle with a half-integer spin (fermion) in the field of an arbitrary inhomogeneous electromagnetic wave has been analysed revealing some features of bound motion defined by so-called optical lattice (channeling). It is shown that, in the first order of expansion in longitudinal energy, the effective interaction potential of a fermion coincides with that of a scalar particle, while the spin features of interaction in this field appear only in the next expansion term. Semiclassical approximation in a spin dynamics for an arbitrary particle in an inhomogeneous optical lattice field indicates that at channeling conditions the polarisation vector affirms a smooth precession, the rate of which is defined by the difference between the magnetic moment of the particle and its anomalous part.

Concessive scalar particles: Symmetric vs. non-symmetric alternatives. The case of Spanish <em>siquiera</em>

Polarity items have been analyzed as existential quantifiers that introduce alternatives into the semantic derivation (Krifka 1991; 1995; Kratzer & Shimoyama 2002; Chierchia 2013). Under this approach, variation in the polarity system can be reduced to variation in the types of alternatives that polarity items introduce (Chierchia 2013). We present a case of dialectal variation within the polarity system that can be treated along these lines. The paper focuses on Spanish siquiera, a concessive scalar particle. Concessive scalar particles (Slovenian magari, Greek esto, and Spanish siquiera) (Crnič 2011a; b) are polarity items licensed in a variety of downward entailing environments, where they can be paraphrased with English even, and in modal environments, where they can be paraphrased with English at least. The paper shows that the interpretation and distribution of Spanish siquiera differs between Iberian and Andean Spanish. We propose that siquiera shares the same assertive core across dialects, but differs in the types of alternatives that it introduces.

Anatomy of the electroweak phase transition for dark sector induced baryogenesis

We investigate the electroweak phase transition patterns for a recently proposed baryogenesis model with CP violation originated in the dark sector. The model includes a complex scalar singlet-Higgs boson portal, a U(1)l gauge lepton symmetry with a Z′ gauge boson portal and a fermionic dark matter particle. We find a novel thermal history of the scalar sector, featuring a Z2 breaking singlet vacuum in the early Universe driven by a dark Yukawa coupling, that induces a one-step strongly first order electroweak phase transition. We explore the parameter space that generates the observed matter-antimatter asymmetry and dark matter relic abundance, while being consistent with constraints from electric dipole moment, collider searches, and dark matter direct detection bounds. The complex singlet can be produced via the Higgs portal and decays into Standard Model particles after traveling a certain distance. We explore the reach for long-lived singlet scalars at the 13 TeV Large Hadron Collider with mathcal{L} = 139 fb−1 and show its impact on the parameter space of the model. Setting aside currently unresolved theoretical uncertainties, we estimate the gravitational wave signatures detectable at future observatories.

A complex singlet extension of the standard model and multi-critical point principle

We study the Multi-critical Point Principle (MPP) in a complex singlet scalar extension of the Standard Model (CxSM). The MPP discussed in this study selects model parameters so that two low-energy vacua realized by scalar fields are degenerate. We further note that the MPP may inhibit the electroweak phase transition (EWPT) in a certain class of models where the tree-level potential plays an essential role in its realization. Despite that, we show that strong first-order EWPT still occurs even after imposing the MPP to the scalar potential of the CxSM due to the 1-loop corrections by the new scalar boson. We study the allowed parameter space where a mass of the additional scalar is degenerate with that of the Standard Model Higgs boson, which provides a built-in mechanism to circumvent constraints from dark matter direct detection experiments. The parameter space for the non-degenerate scalar scenario is also studied for comparison.

Competing instabilities at long length scales in the one-dimensional Bose-Fermi-Hubbard model at commensurate fillings

We study the phase diagram of the one-dimensional Bose-Fermi-Hubbard model at unit filling for the scalar bosons and half filling for the $S=1/2$ fermions using quantum Monte Carlo simulations. The bare interaction between the fermions is set to zero. A central question of our study is what type of interactions can be induced between the fermions by the bosons, for both weak and strong interspecies coupling. We find that the induced interactions can lead to competing instabilities favoring phase separation, superconducting phases, and density wave structures, in many cases at work on length scales of more than 100 sites. Marginal bosonic superfluids with a density matrix decaying faster than what is allowed for pure bosonic systems with on-site interactions, are also found.

First Probe of Sub-GeV Dark Matter beyond the Cosmological Expectation with the COHERENT CsI Detector at the SNS

The COHERENT Collaboration searched for scalar dark matter particles produced at the Spallation Neutron Source with masses between 1 and 220 MeV/c^{2} using a CsI[Na] scintillation detector sensitive to nuclear recoils above 9 keV_{nr}. No evidence for dark matter is found and we thus place limits on allowed parameter space. With this low-threshold detector, we are sensitive to coherent elastic scattering between dark matter and nuclei. The cross section for this process is orders of magnitude higher than for other processes historically used for accelerator-based direct-detection searches so that our small, 14.6kg detector significantly improves on past constraints. At peak sensitivity, we reject the flux consistent with the cosmologically observed dark-matter concentration for all coupling constants α_{D}<0.64, assuming a scalar dark-matter particle. We also calculate the sensitivity of future COHERENT detectors to dark-matter signals which will ambitiously test multiple dark-matter spin scenarios.

Distinguishing nonstandard scalar and fermionic charged particles at a future e+e− collider

We investigate the possibility to identify the nature of spin of exotic charged particles at the future $e^+e^-$ collider in $l^\pm+2j+MET$ final state choosing IDM and MSSM as examples for the new physics models with scalar and fermionic exotic charged particles, respectively. We choose four benchmarks for the mass parameters for a significant deviation from the SM $W^+W^-$ background. We find that the $\cos\theta$ of $W$ boson constructed from $jj$ pair and lepton have the potential to identify the MSSM signal compared to the IDM signal in longitudinally polarized initial beams. A more robust comparison is seen in the shape of the azimuthal angle of the $W$ boson and charged lepton, which can identify the IDM signal further if the beams are transversely polarized.

The -order Foldy–Wouthuysen Hamiltonian and relativistic corrections to Coulomb systems

The order nonrelativistic Hamiltonians of scalar, spinor and vector particles in the electromagnetic field are studied by applying the Douglas–Kroll–Hess approach. The result of the spin-1/2 spinor agrees with the Hamiltonian of the nonrelativistic quantum electrodynamics (Zhou et al 2019 Phys. Rev. A 100 012513). Additionally, the -order relativistic correction to few-electron Coulomb systems and the -order relativistic correction to two-electron Coulomb systems are derived. The singularities of Hamiltonians of Coulomb systems are separated out and cancelled. The regularized Hamiltonians up to -order for scalar and electron in the Coulomb field are obtained. Their numerical results agree with the relativistic theory. The regularized Hamiltonian, up to for few-electrons in the Coulomb field, is also derived.

Measurement of the very rare decay at the NA62 experiment

The decay, with a very precisely predicted branching ratio of less than 10−10, is among the best processes to reveal indirect effects of new physics. The NA62 experiment reports the branching ratio measurement BR() = ± 0.009| syst ) · 10−10 at 68% CL, based on the observation of 20 signal candidates with an expected background of 7.0 events from the total data sample collected at the CERN SPS during 2016-2018. This provides evidence for the very rare decay, observed with a significance of 3.4σ. This measurement is also used to set limits on BR(K + → π +X), where X is a new feebly interacting scalar or pseudo-scalar particle, foreseen in several new physics scenarios.

Evolution of scalar field resonances in a braneworld

In this work, we investigate the numerical evolution of massive Kaluza–Klein (KK) modes of a scalar field in a thick brane. We derive the Klein–Gordon equation in five-dimensional spacetime, and obtain the evolution equation and the Schrödinger-like equation. With the resonances of the scalar KK modes as the initial data, the scalar field is evolved with the maximally dissipative boundary condition. The results show that there are scalar KK resonant particles with long life on the brane, which indicates that these resonances might be regarded as a candidate for dark matter.