International Journal of Modern Physics A

After the last missing piece, the Higgs particle, has probably been identified, the Standard Model of the subatomic particles appears to be a quite robust structure, that can survive on its own for a long time to come. Most researchers expect considerable modifications and improvements to come in the near future, but it could also be that the Model will stay essentially as it is. This, however, would also require a change in our thinking, and the question remains whether and how it can be reconciled with our desire for our theories to be “natural”.

We show a simple mechanism for a dynamical CPT violation in the neutron sector. In particular, we show a CPT-violating see-saw mechanism, generating a Majorana mass and a CPT-violating mass for the neutron. CPT-violating see-saw involves a sterile partner of the neutron, living in a hidden sector, in which CPT is spontaneously broken. In particular, neutrons (antineutrons) can communicate with the hidden sector through nonperturbative quantum gravity effects called exotic instantons. Exotic instantons dynamically break R-parity, generating one effective vertex between the neutron and its sterile partner. In this way, we show how a small CPT-violating mass term for the neutron is naturally generated. This model can be tested in the next generation of experiments in neutron–antineutron physics. This strongly motivates researches of CPT-violating effects in neutron–antineutron physics as a test-bed for dynamical CPT-violations in SM.

The latest LHC data suggest an intriguing excess at $m_{\gamma \gamma }=750\mathrm{\text{GeV}}$ which apparently requires an explanation from the beyond standard model physics. In this paper, we explore the possibility for this signal to arise from a top-pion in the Top Triangle Moose model which can be viewed as a dimensional-deconstruction version of the top-color assisted technicolor model. We demonstrate that the observed excess can be accommodated by and has important implications for this interesting model.

We show that the introduction of a minimal length in the context of noncommutative space–time gives rise (after some considerations) to higher-order theories. We then explicitly demonstrate how these higher-derivative theories appear as a generalization of the standard electromagnetism and general relativity by applying a consistent procedure that modifies the original Maxwell and Einstein–Hilbert actions. In order to set a bound on the minimal length, we compare the deviations from the inverse-square law with the potentials obtained in the higher-order theories and discuss the validity of the results. The introduction of a quantum bound for the minimal length parameter $\sqrt{\beta }$ in the higher-order QED allows us to lower the actual limits on the parameters of higher-derivative gravity by almost half of their order of magnitude.

We study two M5-branes on $A_1$ ALE space. We introduce some M2-branes suspended between the M5-branes. Then, the boundaries of M2-branes look like strings. We call them “M-strings.” The M-strings have ${𝒩}=(4,0)$ supersymmetry by considering the brane configuration on $A_1$ ALE space. We calculate the partition function of M-strings by using the refined topological vertex formalism. We find that the supersymmetry of M-strings gets enhanced to ${𝒩}=(4,4)$ by tuning some Kähler parameters. Furthermore, we discuss another possibility of the enhancement of supersymmetry which is different from the above one.

We consider a new mass scale $M_T={({\hslash }^2\sqrt{\mathrm{\Lambda }}/G)}^{1/3}$ constructed from dimensional analysis by using $G$, $\hslash$ and $\mathrm{\Lambda }$ and discuss its physical interpretation. Based on the Generalized Uncertainty Relation, a black hole with age comparable to the universe would stop radiating when the mass reaches a new mass scale $M_T^{\prime }=c{(\hslash /G^2\sqrt{\mathrm{\Lambda }})}^{1/3}$ at which its temperature corresponds to the mass $M_T$. Black hole remnants could have masses ranging from a Planck mass to a trillion kilograms. Holography persists even when the uncertainty relation is modified to the Minimum Length Uncertainty Relation (MLUR). The remnant black hole entropy is proportional to the surface area of the black hole in unit of the Planck area in arbitrary noncompact dimensions.

We construct the lowest higher spin-2 current in terms of the spin-1 and the spin-$\frac{1}{2}$ currents living in the orthogonal $\frac{SO(N+4)}{SO(N)\times SO(4)}$ Wolf space coset theory for general $N$. The remaining 15 higher spin currents are determined. We obtain the three-point functions of bosonic (higher) spin currents with two scalars for finite $N$ and $k$ (the level of the spin-1 current). By multiplying $SU(2)\times U(1)$ into the above Wolf space coset theory, the other 15 higher spin currents together with the above lowest higher spin-2 current are realized in the extension of the large ${𝒩}=4$ linear superconformal algebra. Similarly, the three-point functions of bosonic (higher) spin currents with two scalars for finite $N$ and $k$ are obtained. Under the large $N$ ’t Hooft limit, the two types of three-point functions in the nonlinear and linear versions coincide as in the unitary coset theory found previously.

Complete expressions of effective Hamilton for $b\to s{l}^{+}{l}^{-}$$(l=\mu ,\tau )$ are derived in the framework of minimal supersymmetric extension of the standard model with local $B-L$ gauge symmetry. With some assumptions on parameters of the model, a numerical analysis of the supersymmetric contributions to the branching ratios of $B_s^0\to l^{+}{l}^{-}$$(l=\mu ,\tau )$ is presented.

The electroweak unification group $SU{(2)}_L\times SU{(2)}_R\times SU{(2)}_Y$ is proposed for the charged lepton flavor violating decays of the muon $(\mu )$ and tau $(\tau )$ leptons. The group $SU{(2)}_Y$ is in the lepton space. The left-handed leptons and antileptons are assigned to the fundamental representation $(2,2,\bar{2})$ of the semi-simple group. The gauge group $SU{(2)}_Y$ is spontaneously broken to $U{(1)}_{Y_1}$, where $Y_1=-L=\pm 1$ is the hypercharge, by introducing a scalar multiplet $\mathrm{\Sigma }$ which belongs to the triplet representation 3 of the $SU{(2)}_Y$ and is singlet under $SU{(2)}_L\times SU{(2)}_R$. At this stage charged vector bosons $Y^{\pm }$ of $SU{(2)}_Y$ which mediate the lepton flavor violating decays acquire masses and are decoupled with one Higgs scalar $H_{\mathrm{\Sigma }}^0$. The residual group $SU{(2)}_L\times SU{(2)}_R\times U{(1)}_{Y_1}$ has all the features of the left–right electroweak unification group extensively studied in the literature. The probability for lepton flavor violating decays is ${\left(\frac{{sin}^2{𝜃}_W}{1-2{sin}^2{𝜃}_W}\right)}^2{\left(\frac{m_{W_L}}{m_Y}\right)}^4$.