International Journal of Modern Physics A

The most important discovery in particle physics in recent years was that of the Higgs boson, and much effort is continuing to measure its properties, which agree obstinately with the Standard Model, so far. However, there are many reasons to expect physics beyond the Standard Model, motivated by the stability of the electroweak vacuum, the existence of dark matter and the origin of the visible matter in the Universe, neutrino physics, the hierarchy of mass scales in physics, cosmological inflation and the need for a quantum theory for gravity. Most of these issues are being addressed by the experiments during Run 2 of the LHC, and supersymmetry could help resolve many of them. In addition to the prospects for the LHC, I also review briefly those for direct searches for dark matter and possible future colliders.

A future Circular Electron Positron Collider (CEPC) has been proposed by China with the main goal of studying the Higgs boson. Its baseline design, chosen on the basis of its performance, is a double ring scheme; an alternative design is a partial double ring scheme which reduces the budget while maintaining an adequate performance. This paper will present the collider ring lattice design for the double ring scheme. The CEPC will also work as a W and a Z factory. For the W and Z modes, except in the RF region, compatible lattices were obtained by scaling down the magnet strength with energy.

We calculate the maximum interior volume, enclosed by the event horizon, of a $(1+D)$-dimensional Schwarzschild black hole. Taking into account the mass change due to Hawking radiation, we show that the volume increases towards the end of the evaporation. This fact is not new as it has been observed earlier for four-dimensional case. The interesting point we observe is that this increase rate decreases towards the higher value of space dimensions $D$; i.e. it is a decelerated expansion of volume with the increase of spatial dimensions. This implies that for a sufficiently large $D$, the maximum interior volume does not change. The possible implications of these results are also discussed.

A single-sided boundary is introduced in the three-dimensional Chern–Simons model. It is shown that only one boundary condition for the gauge fields is possible, which plays the twofold role of chirality condition and bosonization rule for the two-dimensional Weyl fermion describing the degrees of freedom of the edge states of the Fractional Quantum Hall Effect. The symmetry on the boundary is derived, which determines the effective two-dimensional action, whose equation of motion coincides with the continuity equation of the Tomonaga–Luttinger theory. The role of Lorentz symmetry and of discrete symmetries on the boundary is also discussed.

The possible existence of an eV-mass sterile neutrino, slightly mixing with ordinary active neutrinos, is not yet excluded by neutrino oscillation experiments. Assuming neutrinos to be Majorana particles, we explore the impact of such a sterile neutrino on the effective neutrino mass of neutrinoless double-beta decays ${〈m〉}_{ee}^{\prime }\equiv m_1^{}|V_{e1}^{}{|}^2{e}^{\mathrm{\text{i}}\rho }+m_2^{}|V_{e2}^{}{|}^2+m_3^{}|V_{e3}^{}{|}^2{e}^{\mathrm{\text{i}}\sigma }+m_4^{}|V_{e4}^{}{|}^2{e}^{\mathrm{\text{i}}\omega }$, where $m_i^{}$ and $V_{ei}^{}$ (for $i=1,2,3,4$) denote respectively the absolute masses and the first-row elements of the $4\times 4$ neutrino flavor mixing matrix $V$, for which a full parametrization involves three Majorana-type CP-violating phases $\{\rho ,\sigma ,\omega \}$. A zero effective neutrino mass $\left|{〈m〉}_{ee}^{\prime }\right|=0$ is possible, no matter whether three active neutrinos take the normal or inverted mass ordering, and its implications for the parameter space are examined in great detail. In particular, given the best-fit values of $m_4^{}\approx 1.3\mathrm{\text{eV}}$ and $|V_{e4}^{}{|}^2\approx 0.019$ from the latest global analysis of neutrino oscillation data, a three-dimensional view of $\left|{〈m〉}_{ee}^{\prime }\right|$ in the $(m_{\mathrm{\text{lightest}}}^{},\rho )$-plane is presented and further compared with that of the counterpart $\left|{〈m〉}_{ee}^{}\right|$ in the absence of any sterile neutrino.

Lorentz symmetry is a fundamental symmetry in the Standard Model (SM) and in General Relativity (GR). This symmetry holds true for all models at low energies. However, at energies near the Planck scale, it is conjectured that there may be a very small violation of Lorentz symmetry. The Standard Model Extension (SME) is a quantum field theory that includes a systematic description of Lorentz symmetry violations in all sectors of particle physics and gravity. In this paper, SME is considered to study the physical process of Bhabha Scattering in the Gravitoelectromagnetism (GEM) theory. GEM is an important formalism that is valid in a suitable approximation of general relativity. A new nonminimal coupling term that violates Lorentz symmetry is used in this paper. Differential cross-section for gravitational Bhabha scattering is calculated. The Lorentz violation contributions to this GEM scattering cross-section are small and are similar in magnitude to the case of the electromagnetic field.

By using the AdS/CFT correspondence, we investigate various form factors between nucleons and mesons in a nuclear medium. In order to describe a nuclear medium holographically, we take into account the thermal charged AdS geometry with an appropriate IR cutoff. After introducing an anomalous dimension as a free parameter, we investigate how the nucleon’s mass is affected by the change of the anomalous dimension. Moreover, we study how the form factors of nucleons rely on the properties of the nuclear medium. We show that in a nuclear medium with different numbers of proton and neutron, the degenerated nucleon form factor in the vacuum is split into four different values depending on the isospin charges of nucleon and meson.

We discuss the constraint on the size of QCD instanton effects in low-energy effective theory. Among various instanton effects in meson mass spectrum and dynamics, we concentrate on the instanton-induced masses of light quarks. The famous instanton-induced six-quark interaction, so-called ’t Hooft vertex, could give nonperturbative quantum corrections to light quark masses. Many works have already been achieved to constrain the mass corrections in light meson system, or the system of $\pi$, $K$, $\eta$ and ${\eta }^{\prime }$, and now we know for a fact that the instanton-induced mass of up-quark is too small to realize the solution of the strong CP problem by vanishing current mass of up-quark. In this work, we give a constraint on the instanton-induced mass correction to light quarks from the mass spectrum of heavy mesons, $B^{+}$, $B^0$, $B_s$ and their antiparticles. To accomplish this, the complete second-order chiral symmetry breaking terms are identified in heavy meson effective theory. We find that the strength of the constraint from heavy meson masses is at the same level of that from light mesons, and it would be made even stronger by more precise data from future $B$ factories and lattice calculations.

In this paper, we describe the quantum electrodynamics added by Lorentz-violating CPT-even terms in the context of the standard model extension. We focus our attention on the fermion sector, represented by the CPT-even symmetric Lorentz-breaking tensor $c_{\mu \nu }$. We adopt a generic form that parametrizes the components of $c_{\mu \nu }$ in terms of one four-vector, namely, $c_{\mu \nu }=u_{\mu }{u}_{\nu }-\zeta \frac{u^2}{4}{g}_{\mu \nu }$. We then generate perturbatively, up to the third order in this tensor, the aether-like term for the gauge field. Finally, we discuss the renormalization scheme for the gauge propagator, by taking into account $c_{\mu \nu }$ traceless $(\zeta =1)$ and, trivially, $c_{\mu \nu }=u_{\mu }{u}_{\nu }$ $(\zeta =0)$.