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1. Deser, S.

et al.

Izumi, K.

Ong, Yen Chin

KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.

Waldron, A.

Problems of massive gravities2015In: Modern Physics Letters A, ISSN 0217-7323, E-ISSN 1793-6632, Vol. 30, no 3-4, article id 1540006Article in journal (Refereed)

Abstract [en]

The method of characteristics is a key tool for studying consistency of equations of motion; it allows issues such as predictability, maximal propagation speed, superluminality, unitarity and acausality to be addressed without requiring explicit solutions. We review this method and its application to massive gravity (mGR) theories to show the limitations of these models' physical viability: Among their problems are loss of unique evolution, superluminal signals, matter coupling inconsistencies and micro-acausality (propagation of signals around local closed time-like curves (CTCs)/closed causal curves (CCCs)). We extend previous no-go results to the entire three-parameter range of mGR theories. It is also argued that bimetric models suffer a similar fate.

We have investigated matter enhanced neutrino oscillations with a mantle-core-mantle step function and a realistic Earth matter density profile in both a two- and a three-neutrino scenario. We found that the realistic Earth matter density profile can be well approximated with the mantle-core-mantle step function and that there could be an influence on the oscillation channel nu(mu) --> nu(tau) due to resonant enhancement of one of the mixing angles.

The T2K experiment has provided the first hint for the best-fit value for the leptonic CP phase delta(CP) similar to -90 degrees from neutrino data. This is now corroborated by the NO nu A neutrino runs. We study the implications for neutrino mass hierarchy and octant of theta(23) in the context of this data assuming that the true value of delta(CP) in nature is -90 degrees. Based on simple arguments on degeneracies in the probabilities, we show that a clear signal of delta(CP) = -90 degrees coming from T2K neutrino (antineutrino) data is only possible if the true hierarchy is normal and the true octant is higher (lower). Thus, if the T2K neutrino and antineutrino data are fitted separately and both give the true value of delta(CP) = -90 degrees, this will imply that nature has chosen the true hierarchy to be normal and theta(23) approximate to 45 degrees. However, we find that the combined fit of neutrino and antineutrino data will still point to true hierarchy as normal but the octant of theta(23) will remain undetermined. We do our analysis for both, the current projected exposure (7.8 x 10(21) pot) and planned extended exposure (20 x 10(21) pot). We also present the CP discovery potential of T2K emphasizing on the role of antineutrinos. We find that one of the main contributions of the antineutrino data is to remove the degenerate solutions with the wrong octant. Thus, the antineutrino run plays a more significant role for those hierarchy-octant combinations for which this degeneracy is present. If this degeneracy is absent, then only neutrino run gives a better result for fixed theta(13). However, if we marginalize over theta(13) then, sensitivity corresponding to mixed run can be better than pure neutrino run.

KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Kharkov Institute of Physics and Technology.

Inflation versus collapse in brane matter2017In: Modern Physics Letters A, ISSN 0217-7323, E-ISSN 1793-6632, Vol. 32, no 36, article id 1750199Article in journal (Refereed)

Abstract [en]

Mapping of fundamental branes to their worldsheet (ws) multiplets originating from spontaneous breaking of the Poincaré symmetry is studied. The interaction Lagrangian for fields of the Nambu-Goldstone multiplet is shown to encode R2 gravity on the ws. The power law kp ∼ Tp 3-p 2(p+1) for the SO(D - p - 1) gauge coupling kp as the function of the p-brane tension Tp is assumed. It points to the presence of asymptotic freedom and confinement phases in brane matter. Their connection with collapse and inflation of the branes is discussed.