Related papers: Constraints on Theories With Large Extra Dimension…
The tentative hints for a diphoton resonance at a mass of $\sim 750$ GeV from the ATLAS and CMS experiments at the LHC may be interpreted as first contact with a "dark" sector with a spontaneously broken conformal symmetry. The implied TeV…
We make a detailed study of the unification of gauge couplings in the MSSM with large extra dimensions. We find some scenarios where unification can be achieved (with the strong coupling constant at the Z mass within one standard deviation…
Recently it has been shown that string gas cosmology, an alternative model of the very early universe which does not involve a period of cosmological inflation, can give rise to an almost scale invariant spectrum of metric perturbations.…
Studies in string theory and quantum gravity suggest the existence of a finite lower limit $\Delta x_0$ to the possible resolution of distances, at the latest on the scale of the Planck length of $10^{-35}m$. Within the framework of the…
This is a pedagogical review article surveying the various approaches towards understanding gauge coupling unification within string theory. As is well known, one of the major problems confronting string phenomenology has been an apparent…
We discuss the stability of atoms and nucleons in the presence of multidimensional gravity characterized by the unified energy scale 1TeV. We point out that the multidimensional gravitational attraction can create additional bound states…
We present an argument in which the scale ~ 0.1 eV associated with neutrino masses naturally appears in a a class of (very) large volume compactifications, being tied to a supersymmetry scale of 10^3 GeV and a string scale of 10^11 GeV. The…
We discuss the entropy and the size/homogeneity/horizon problems in power-law expanding universes with one scale initial conditions. We set the minimal scale $\Lambda = 10^{25}$ GeV at which a non-inflationary solution is possible and show…
We propose a lower limit on the size of a single discrete gravitational extra dimension in the context of an effective field theory for massive gravitons. The limit arises in this setup from the requirement that the Casimir energy density…
We argue for a relation between the supersymmetry breaking scale and the measured value of the dark energy density $\Lambda$. We derive it by combining two quantum gravity consistency swampland constraints, which tie the dark energy density…
We construct a left-right symmetric (LRS) model in five dimensions which accounts naturally for the lepton flavor parameters. The fifth dimension is described by an orbifold, S_1/Z_2 times Z'_2, with a typical size of order TeV^{-1}. The…
We report a search for effects of large extra spatial dimensions in ppbar collisions at a center-of-mass energy of 1.8 TeV with the DZero detector, using events containing a pair of electrons or photons. The data are in good agreement with…
The minimal supersymmetric standard model (MSSM), is perhaps the leading candidate for new physics beyond the standard model, but it encounters difficulties with string gauge unification and in addition does not shed any light on the…
For a top quark mass fixed to its measured value, we find natural regions of minimal supergravity parameter space where all squarks, sleptons, and heavy Higgs scalars have masses far above 1 TeV and are possibly beyond the reach of the…
We construct tree-level four-particle open-string amplitudes relevant to dilepton and diphoton production at hadron colliders. We expand the amplitudes into string resonance (SR) contributions and compare the total cross-section through the…
We present an analysis of the low-energy implications of an intermediate scale ~10^{11} GeV string theory. We mainly focus on the evolution of the physical parameters under the renormalisation group equations (RGEs) and find several…
I consider a class of Grand Unified models, in which E8 is broken to SU(3)xSU(2)xSU(2)xSU(2)xU(1)_Y, then to SU(3)xSU(2)_{diag}xU(1)_Y. The breaking of (SU(2))^3 to SU(2)_{diag} reduces the SU(2) coupling constant, at unification, by a…
Cosmic strings can arise in hidden sector models with a spontaneously broken Abelian symmetry group. We have studied the couplings of the Standard Model fields to these so-called dark strings in the companion paper. Here we survey the…
Ten reasons are given why supersymmetry is the leading candidate for physics beyond the Standard Model. Ultimately, the experimental discovery of supersymmetric particles at future colliders will determine whether supersymmetry is relevant…
We estimate the rate at which collisions between ultra-high energy cosmic rays can form small black holes in models with extra dimensions. If recent conjectures about false vacuum decay catalyzed by black hole evaporation apply, the lack of…