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Register a new userLight Speed Variation in a String Theory Model for Space-Time Foam
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We revisit a supersymmetric string model for space-time foam, in which bosonic open-string states, such as photons, can possess quantum-gravity-induced velocity fluctuations in vacuum. We argue that the suggestion of light speed variation with lower bound from gamma-ray burst photon time delays can serve as a support for this string-inspired framework, through connecting the experimental finding with model predictions. We also derive the value of the effective quantum-gravity mass in this framework, and give a qualitative study on the model-dependent coefficients. Constraints from birefringent effects and/or photon decays, including the novel $gamma$-decay constraint obtained here from the latest Tibet AS$gamma$ near-PeV photon, are also found to be consistent with predictions in such a quantum-gravity scheme. Future observation that can testify further the theory is suggested.
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Recently a series of studies on high energy gamma-ray burst~(GRB) photons suggest a light speed variation with linear energy dependence at the Lorentz violation scale of $3.6 times 10^{17}~mathrm{GeV}$, with subluminal propagation of high energy photons in cosmological space. We propose stringy space-time foam as a possible interpretation for this light speed variation. In such a string-inspired scenario, bosonic photon open-string travels textit{in vacuo} at an infraluminal speed with an energy dependence suppressed by a single power of the string mass scale, due to the foamy structure of space-time at small scales, as described by D-brane objects in string theory. We present a derivation of this deformed propagation speed of the photon field in the infrared (IR) regime. We show that the light speed variation, revealed in the previous studies on GRBs time-delay data, can be well described within such a string approach towards space-time foam. We also derive the value of the effective quantum-gravity mass in this framework, and give a qualitative study on the theory-dependent coefficients. We comment that stringent constraints on Lorentz violation in the photon sector from complementary astrophysical observations can also be explained and understood in the space-time foam context.
We calculate the atmospheric flux of prompt neutrinos, produced in decays of the charmed particles at energies beyond 1 TeV. Cross sections of the $D$-mesons and ${Lambda}^{+}_{c}$ baryons production in pA and $pi$A collisions are calculated in the phenomenological quark-gluon string model (QGSM) which is updated using of the recent measurements of cross sections of the charmed meson production in the LHC experiments. A new estimate of the prompt atmospheric neutrino flux is obtained and compared with the limit of the IceCube experiment as well as with predictions of other charm production models.
We try to interpret a very light dark matter with mass of 5~10 GeV which is in favor of the recent experiments reported by CoGeNT and DAMA, in a non-supersymmetric extension of radiative seesaw model with a family symmetry D_6 x Z_2 x Z_2. We show that a D_6 singlet real scalar field can be a promising dark matter candidate, and it gives the elastic cross section sigma simeq 7x10^{-41} cm^2 which is required by these experiments. Our dark matter interacts with a D_6 singlet scalar Higgs boson, which couples only to quark sector. The dark matter-nucleon cross section and new decay mode h->DM DM can be large if the standard model Higgs boson h is light. The Higgs phenomenology is also discussed.
This paper presents a compelling argument for the physical light speed in the Friedman-Lemaitre-Robertson-Walker (FLRW) universe to vary with the cosmic time coordinate t of FLRW. It must be variable when the radial comoving differential coordinates of FLRW is interpreted as physical and therefore transformable by a Lorentz transform locally to differentials of stationary physical coordinates. Because the FLRW differential radial distance has a time varying coefficient a(t), integration of the transformed differentials to obtain stationary coordinates for a short radial distance requires the light speed c(t) to be proportional to the square root of da/dt. Since we assume homogeneity of space, this derived c(t) is the physical light speed on all points of the FLRW universe. This impacts the interpretation of all astronomical observations of distant phenomena that are sensitive to light speed. A world transform from FLRW that has a Minkowski metric close to the origin is shown to have a physical radius out to all points of the visible universe. In order to obtain numerical values for c(t), the general relativity (GR) field equation is extended by using a variable gravitational constant and rest mass that keeps constant the gravitational and particle rest energies. This also keeps constant the proportionality constant between the GR tensors of the field equation and conserves the rest stress-energy tensor of the ideal fluid used in the FLRW GR field equation. In the same way all of special and general relativity is extended to include a variable light speed.
We construct a string theory in three-dimensional anti-de Sitter space-time that is independent of the boundary metric. It is a topologically twisted theory of quantum gravity. We study string theories with an asymptotic N=2 superconformal symmetry and demonstrate that, when the world sheet coupling to the space-time boundary metric undergoes a U(1) R-symmetry twist, the space-time boundary energy-momentum tensor becomes topological. As a by-product of our analysis, we obtain the world sheet vertex operator that codes the space-time energy-momentum for conformally flat boundary metrics.
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