SLAC Report SLACR972
SLAC Release Date: September 19, 2012
Search for Large Extra Dimensions Based on Observations of Neutron Stars with the FermiLAT
Berenji, B.
According to the Large Extra Dimensions (LED) model of ArkaniHamed, Dimopoulos, and Dvali (ADD), in addition to the (3+1) observed spacetime dimensions, there exist n gravityonly spatial dimensions. Due to the presence of the additional dimensions, the Planck scale of gravity should be brought down from 1E16 TeV to the TeV scale, near the electroweak scale, and thus solve the hierarchy problem. Based on the ADD theory, KaluzaKlein (KK) gravitons, having masses of the order 100 MeV and lifeti...
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According to the Large Extra Dimensions (LED) model of ArkaniHamed, Dimopoulos, and Dvali (ADD), in addition to the (3+1) observed spacetime dimensions, there exist n gravityonly spatial dimensions. Due to the presence of the additional dimensions, the Planck scale of gravity should be brought down from 1E16 TeV to the TeV scale, near the electroweak scale, and thus solve the hierarchy problem. Based on the ADD theory, KaluzaKlein (KK) gravitons, having masses of the order 100 MeV and lifetimes of the order of billions of years, are expected to be produced within supernova cores by nucleonnucleon gravibremsstrahlung in the LED model. Once produced, they are predicted to be trapped by the gravitational potential of subsequently formed neutron stars (NS), and their decay is predicted to contribute to a measurable gammaray flux from NS. In this dissertation, refinements to past theoretical models are made, including modifications for the expected spectral energy distribution based on orbital motion of the gravitons, and NS surface magnetic field and age. n = 2,3, ..., 7 extra dimensions are considered. A sample of 6 gammaray faint NS sources not reported in the first Fermi gammaray source catalog that are good candidates are selected for this analysis, based on age, surface magnetic field, distance, and galactic latitude. Based on 11 months of data from Fermi LAT, 95% CL upper limits on the size of extra dimensions R from each source are obtained, as well as 95% CL lower limits on the (n+4)dimensional Planck scale M_D. In addition, the limits from all of the analyzed NSs have been combined statistically using two likelihoodbased methods. The results indicate more stringent limits on LED than quoted previously from individual neutron star sources in gammarays. In addition, the results are more stringent than current collider limits, from the LHC, for n < 4. If the Planck scale is around a TeV, then for n = 2,3, the compactification topology of LED must be more complicated than a torus.
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Interest Categories: Astrophysics, Gravitation and Cosmology, HEP Phenomenology
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