Aspects of Particle Physics and Cosmology from String/M Theory

This thesis is focused on various aspects of particle physics and cosmology fromString/M theory. Assuming our universe is a solution of string/M theory, physicsbelow the unication scale is an eective 4D supergravity theory with an abundanceof moduli and axions. The phenomenology of moduli and axions in an earlyuniverse is studied. We particularly study dark radiation constraints on a genericAxiverse scenario and provide various solutions to it. The simplest solution requires the lightest modulus decays only into its own axion superpartner and this severely constrains the moduli Kahler potential and mass matrix. We also study a model building aspect of string/M theory. It has been shown that a discrete symmetry on a manifold with G2 holonomy combined with symmetry breaking Wilson lines provide a solution to the doublet-triplet splitting problem. We extend the idea to a new class of model based on M theory compactied on a G2 manifold which leads to a novel solution where the colour triplets are decoupled. The models also involves an extra vector-like standard model multiplet to restore gauge unication. We will also discuss the phenomenology of the new light states and the induced R-parity violation. We will also study the prospects of searches from a future generation of colliders. We focus in particular on the search at a 100 TeV collider via the WZ channel. The motivation from string/M theory models leads to the assumption that Higgsinos form the lightest supersymmetric particle. We design simple signal regions for the trilepton channel and nd that neutralinos-charginos could be discovered(excluded) up to 1.1 (1.8) TeV

Bounds on ALP-Mediated Dark Matter Models from Celestial Objects

We have studied the signals from axion-like particles (ALPs) as dark matter mediators from celestial objects such as neutron stars or brown dwarfs. We consider the accumulation of dark matter inside the celestial objects using the multiscatter capturing process. The production of ALP from the dark matter annihilation can escape the celestial object and decay into gamma-ray and neutrinos before reaching the Earth. We investigate our model using gamma-ray observations from Fermi and H.E.S.S and neutrino observations from IceCube and ANTARES. The effective Lagrangian approach allows us to place constraints on the ALP-photon and ALP-fermion couplings. In the gamma-ray channel, our results improve the existing bounds on ALPs by 1-2 orders of magnitude. Although the constraints from neutrino fluxes rule out a significant portion of the parameter space, the remaining part of the parameter space is accessible by future experiments.Comment: 17 pages, 9 figure

A Kaluza-Klein Inspired Brans-Dicke Gravity with Dark Matter and Dark Energy Model

We propose the Kaluza-Klein inspired Brans-Dicke gravity model containing possible existence of dark matter and dark energy. The massive scalar field coupled with gravity in 5 dimensional spacetime can be reduced to 4 dimensional gravity along with the dilaton $\phi$, gauge fields $A_{\mu}$, and the tower of scalar fields $\eta_n$. Two additional gauge fields are introduced to form "Cosmic Triad" vector field scenario. We then use the dynamical system approach to analyze the critical points and their corresponding physical parameters. We found that in the case where only the zero mode of the Kaluza-Klein scalar is decoupled, the system contains both dark matter and dark energy phase depending on the mass parameter with the presence of the gauge field.Comment: 29 pages, 2 figure

Dark Matter and Dark Energy from a Kaluza-Klein inspired Brans-Dicke Gravity with Barotropic Fluid

We study the Kaluza-Klein inspired Brans-Dicke model with barotropic matter. Following from our previous work, the traditional Kaluza-Klein gravity action is introduced with an additional scalar field and 2 gauge fields. The compactification process results in a Brans-Dicke model with a dilaton coupled to the tower of scalar fields whereas a gauge field from 5-dimensional metric forms a set of mutually orthogonal vectors with 2 additional gauge fields. The barotropic matter is then introduced to complete a realistic set up. To demonstrate the analytical solutions of the model, we consider the case in which only 2 lowest modes becoming relevant for physics at low scale. After derivation, equations of motion and Einstein field equations form a set of autonomous system. The dynamical system is analysed to obtain various critical points. Interestingly, by only inclusion of barotropic matter, the model provides us the critical points which capable of determining the presences of dark matter, dark energy and phantom dark energy.Comment: 34 pages, 9 figures, 1 tabl

Neutrino mass from M Theory SO(10)

We study the origin of neutrino mass from $SO(10)$ arising from $M$ Theory compactified on a $G_2$-manifold. This is linked to the problem of the breaking of the extra $U(1)$ gauge group, in the $SU(5)\times U(1)$ subgroup of $SO(10)$, which we show can achieved via a (generalised) Kolda-Martin mechanism. The resulting neutrino masses arise from a combination of the seesaw mechanism and induced R-parity breaking contributions. The rather complicated neutrino mass matrix is analysed for one neutrino family and it is shown how phenomenologically acceptable neutrino masses can emerge.Comment: 32 pages, 12 figure

SO(10) Grand Unification in M theory on a G2 manifold

We consider Grand Unified Theories based on $SO(10)$ which originate from string/$M$ theory on $G_2$ manifolds or Calabi-Yau spaces with discrete symmetries. In this framework we are naturally led to a novel solution of the doublet-triplet splitting problem previously considered by Dvali which involves an extra vector-like Standard Model family and light, but weakly coupled colour triplets. These additional states are predicted to be accessible at the LHC and also induce R-parity violation. Gauge coupling unification occurs with a larger GUT coupling.Comment: 5 pages, added references, revised argument on equation 18, results unchanged, a new example is given in equation 24, agrees with published version in Physical Review

Prospects for observing charginos and neutralinos at a 100 TeV proton-proton collider

We investigate the prospects for discovering charginos and neutralinos at a future $pp$ collider with $\sqrt{s} = 100$ TeV. We focus on models where squarks and sleptons are decoupled -- as motivated by the LHC data. Our initial study is based on models where Higgsinos form the main component of the LSP and $W$-inos compose the heavier chargino states ($M_2 > \mu$), though it is straightforward to consider the reverse situation also. We show that in such scenarios $W$-inos decay into $W^\pm$, $Z$ and $h$ plus neutralinos almost universally. In the $W Z$ channel we compare signal and background in various kinematical distributions. We design simple but effective signal regions for the trilepton channel and evaluate discovery reach and exclusion limits. Assuming 3000 fb$^{-1}$ of integrated luminosity, $W$-inos could be discovered (excluded) up to 1.1 (1.8) TeV if the spectrum is not compressed.Comment: 19 pages, 9 figure

Effects of odderon spin on helicity amplitudes in pppp elastic scattering

In recent years, the discovery of the odderon, a colorless $C$-odd gluonic compound, has been confirmed in the TOTEM and D0 collaborations. However, the spin quantum number of the odderon remains unidentified. In this work, we aim to attribute a spin of $J=3$ to the odderon in $pp$ elastic scattering by calculating the helicity amplitudes and the corresponding complex parameter $r_5$, the ratio of helicity's single-flip to non-flip amplitudes, for the spin-3 tensor odderon with the standard spin-2 tensor pomeron exchanges. Then, we apply these results to the constraints obtained from the STAR experiment at RHIC. By comparing to the contributions of the spin-1 vector odderon and spin-2 tensor pomeron, we demonstrate that the spin-3 tensor odderon, i.e. $J=3$, provides a better explanation for the observable in $pp$ elastic scattering.Comment: 11 pages, 2 figure