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Many models of physics beyond the Standard Model predict minicharged particles to which current and near future low-energy experiments are highly sensitive. Such minicharges arise generically from kinetic-mixing in theories containing at…
The charge-hiding effect by a horned particle, which was studied for the case where gravity/gauge-field system is self-consistently interacting with a charged lightlike brane (LLB) as a matter source, is now studied for the case of a time…
The S-matrix theory formulation of closed-orbit theory recently proposed by Granger and Greene is extended to atoms in crossed electric and magnetic fields. We then present a semiclassical quantization of the hydrogen atom in crossed…
Electrically as well as magnetically charged states are constructed in the 2+1-dimensional Euclidean Z_N-Higgs lattice gauge model, the former following ideas of Fredenhagen and Marcu and the latter using duality transformations on the…
It was recently proposed that stable particles of charge $-2$, $O^{--}$, can exist and constitute dark matter after they bind with primordial helium in O-helium (OHe) atoms. We study here in details the possibility that this model provides…
In this thesis, we explore two approaches to string phenomenology. In the first half of the work, we investigate M-theory compactifications on spaces with co-dimension four, orbifold singularities. We construct M-theory on C^2/Z_N by…
For a quantum field of arbitrary mass and spin in the static patch of de Sitter spacetime, the Euclidean partition function receives contributions from edge modes localized on the horizon, expressible in terms of the Harish-Chandra…
Supermassive black holes (SMBHs) are found in the centers of massive galaxies, and galaxy mergers should eventually lead to SMBH mergers. Quasar activity has long been associated with galaxy mergers, so here we investigate if supermassive…
Supermassive black holes (SMBHs; $M\gtrsim10^5\msun$) are known to exist at the centre of most galaxies with sufficient stellar mass. In the local Universe, it is possible to infer their properties from the surrounding stars or gas.…
We study orbifold compactifications of heterotic strings on Enriques surfaces. We classify the inequivalent shift vectors for both the E8\times E8 and Spin(32)/Z2 lattices, and analyse the light spectrum of the resulting models. We show…
We revisit the old black hole S-Matrix construction and its new partial wave expansion of 't Hooft. Inspired by old ideas from non-critical string theory & $c=1$ Matrix Quantum Mechanics, we reformulate the scattering in terms of a quantum…
We study the charge ordering behavior under a magnetic field $H$ in the extended Hubbard model within the coherent potential approximation. At quarter filling, for small $H$ we find that the relative variation of critical temperature is…
Almost all extensions of the Standard Model predict the existence of charged Higgs bosons. This talk focuses on the minimal supersymmetric extension of the Standard Model (MSSM), which is relatively predictive. The outlook for detecting…
We continue the study of a class of string-motivated effective supergravity theories in light of current data from the CERN Large Hadron Collider (LHC). In this installment we consider Type IIB string theory compactified on a Calabi-Yau…
We compute the path integral for a particle on the covering group of SL(2,R) using a decomposition of the Lie algebra into adjoint orbits. We thus intuitively derive the Hilbert space of the particle on the group including discrete and…
Based on geometric phases of Bloch electrons computed from first-principles, we propose a scheme for unambiguous partitioning of charge in matter, derivable directly from the Kohn-Sham states. Generalizing the fact that geometric phases…
We use heterotic/type-II prepotentials to study quantum/classical black holes with half the $N=2, D=4$ supersymmetries unbroken. We show that, in the case of heterotic string compactifications, the perturbatively corrected entropy formula…
We study BPS bound states of little strings in a limit where they realise monopole strings in five dimensional gauge theories. The latter have gauge group $U(M)^N$ and arise from compactification of $(1,0)$ little string theories of type…
Heavy stable charged particles can exist, hidden from us in bound atomlike states. Models with new stable charged leptons and quarks give rise to realistic composite dark matter scenarios. Significant or even dominant component of O-helium…
The nonbaryonic dark matter of the Universe is assumed to consist of new stable particles. Stable particle candidates for cosmological dark matter are usually considered as neutral and weakly interacting. However stable charged leptons and…