International Journal of Modern Physics A

The journey in search for the Higgs boson with the ATLAS and CMS experiments at the Large Hadron Collider (LHC) at CERN started more than two decades ago. But the first discussions motivating the LHC project dream date back even further into the 1980s. This article will recall some of these early historical considerations, mention some of the LHC machine milestones and achievements, focus as an example of a technological challenge on the unique ATLAS superconducting magnet system, and then give an account of the physics results so far, leading to, and featuring particularly, the Higgs boson results, and sketching finally prospects for the future. With its emphasis on the ATLAS experiment it is complementary to the preceding article by Tejinder S. Virdee which focused on the CMS experiment.

The absence of the quadratic divergence in the Higgs sector of the Standard Model in the dimensional regularization is usually regarded to be an exceptional property of a specific regularization. To understand what is going on in the dimensional regularization, we illustrate how to reproduce the results of the dimensional regularization for the $\lambda {\varphi }^4$ theory in the more conventional regularization such as the higher derivative regularization; the basic postulate involved is that the quadratically divergent induced mass, which is independent of the scale change of the physical mass, is kinematical and unphysical. This is consistent with the derivation of the Callan–Symanzik equation, which is a comparison of two theories with slightly different masses, for the $\lambda {\varphi }^4$ theory without encountering the quadratic divergence. In this sense the dimensional regularization may be said to be generic in a bottom-up approach starting with a successful low energy theory. We also define a modified version of the mass independent renormalization for a scalar field which leads to the homogeneous renormalization group equation. Implications of the present analysis on the Standard Model at high energies and the presence or absence of SUSY at LHC energies are briefly discussed.

Abdus Salam was a true master of 20th Century Theoretical Physics. Not only was he a pioneer of the Standard Model (for which he shared the Nobel Prize with S. Glashow and S. Weinberg), but he also (co)authored many other outstanding contributions to the field of Fundamental Interactions and their unification. In particular, he was a major contributor to the development of supersymmetric theories, where he also coined the word “Supersymmetry” (replacing the earlier “Supergauges” drawn from String Theory). He also introduced the basic concept of “Superspace” and the notion of “Goldstone Fermion” (Goldstino). These concepts proved instrumental for the exploration of the ultraviolet properties and for the study of spontaneously broken phases of super Yang–Mills theories and Supergravity. They continue to play a key role in current developments in Early-Universe Cosmology. In this contribution we review models of inflation based on Supergravity with spontaneously broken local supersymmetry, with emphasis on the role of nilpotent superfields to describe a de Sitter phase of our Universe.

For a test particle approaching a rapidly rotating black hole we find a range of values of the particle’s energy and angular momentum, on the order of 1% or more of the corresponding values of the hole, such that three conditions are satisfied. (1) The particle can reach the horizon. (2) After absorption the new hole still has a horizon. (3) The area of the new hole is less than the area of the original one, in apparent violation of a theorem of Hawking. We offer support for the claim that the test particle approximation is the cause of the violation.

We summarize the impact of sterile neutrino dark matter on core-collapse supernova explosions. We explore various oscillations between electron neutrinos or mixed $\mu -\tau$ neutrinos and right-handed sterile neutrinos that may occur within a core-collapse supernova. In particular, we consider sterile neutrino masses and mixing angles that are consistent with sterile neutrino dark matter candidates as indicated by recent X-ray flux measurements. We find that the interpretation of the observed 3.5 keV X-ray excess as due to a decaying 7 keV sterile neutrino that comprises 100% of the dark matter would have almost no observable effect on supernova explosions. However, in the more realistic case in which the decaying sterile neutrino comprises only a small fraction of the total dark matter density due to the presence of other sterile neutrino flavors, WIMPs, etc. a larger mixing angle is allowed. In this case a 7 keV sterile neutrino could have a significant impact on core-collapse supernovae. We also consider mixing between $\mu -\tau$ neutrinos and sterile neutrinos. We find, however, that this mixing does not significantly alter the explosion and has no observable effect on the neutrino luminosities at early times.

We perform the perturbative generation of the higher-derivative Chern–Simons contribution to the effective action in the three-dimensional QED at zero and finite temperatures. In the latter case, we show that as the temperature goes to infinity this contribution vanishes. However, as expected, as the temperature goes to zero only the covariant part survives. The noncovariant part contributes only in intermediate temperatures where it presents a maximum.

We study the neutrino mass generation in the $SU{(4)}_L\otimes U{(1)}_X$ electroweak extension of the Standard Model by considering nonrenormalizable dimension 5 effective operators. It is shown that there exist two topologies for the realizations of such an operator at the tree-level and for one of the three-family models the neutrino phenomenology is explored after extending its particle content with an $SU{(4)}_L$ fermion singlet and a scalar decuplet. Constraints in the available parameters space of the model are partially discussed.

We investigate the dependence of non-Abelian T-duality on various identification of the isometry group of target space with its orbits, i.e. with respect to the location of the group unit on manifolds invariant under the isometry group. We show that T-duals constructed by isometry groups of dimension less than the dimension of the (pseudo)-Riemannian manifold may depend not only on the initial metric but also on the choice of manifolds defining positions of group units on each of the submanifold invariant under the isometry group. We investigate whether this dependence can be compensated by coordinate transformation.

In this paper, we present a new mathematical rigorous technique for computing the average free energy of a disordered system with quenched randomness, using the replicas. The basic tool of this technique is a distributional zeta-function, a complex function whose derivative at the origin yields the average free energy of the system as the sum of two contributions: the first one is a series in which all the integer moments of the partition function of the model contribute; the second one, which cannot be written as a series of the integer moments, can be made as small as desired. This result supports the use of integer moments of the partition function, computed via replicas, for expressing the average free energy of the system. One advantage of the proposed formalism is that it does not require the understanding of the properties of the permutation group when the number of replicas goes to zero. Moreover, the symmetry is broken using the saddle-point equations of the model. As an application for the distributional zeta-function technique, we obtain the average free energy of the disordered $\lambda {\phi }^4$ model defined in a $d$-dimensional Euclidean space.

In this paper, we study the recent 750 GeV diphoton excess in the Hill model with vector-like fermions. The singlet-like Hill boson is chosen as the 750 GeV diphoton resonance. Such a scalar is mainly produced by gluon fusion via vector-like top and bottom quark loops and decays to diphoton via the vector-like quark and lepton loops. Under the current experimental and theoretical constraints, we find that the mixing angle of the singlet and doublet Higgs bosons lies within $|sin𝜃|\lesssim 0.03$ and the 750 GeV diphoton cross-section can be maximally enhanced to about 6 fb at 13 TeV LHC. Moreover, we find that the Hill boson pair production in $jj\gamma \gamma$ channel can be probed at $3\sigma$ significance if $375\mathrm{\text{GeV}}<m_F<1500\mathrm{\text{GeV}}$ and $1.4<y_F<3$ at a 100 TeV collider with 3000 fb${}^{-1}$ luminosity.