Double Soft Graviton Theorems and BMS Symmetries

It is now well understood that Ward identities associated to the (extended) BMS algebra are equivalent to single soft graviton theorems. In this work, we show that if we consider nested Ward identities constructed out of two BMS charges, a class of double soft factorization theorems can be recovered. By making connections with earlier works in the literature, we argue that at the sub-leading order, these double soft graviton theorems are the so-called consecutive double soft graviton theorems. We also show how these nested Ward identities can be understood as Ward identities associated to BMS symmetries in scattering states defined around (non-Fock) vacua parametrized by supertranslations or superrotations.Comment: 29 pages, minor changes added, footnote 3 removed, consistency check with Ref:22 settle

Radion Cosmology in Theories with Universal Extra Dimensions

We discuss cosmology of models with universal extra dimensions, where the Standard Model degrees of freedom live in a $4+n$ dimensional brane, with $n$ compact and small extra spatial dimensions. In these models, the simplest way to obtain the conventional 4-dimensional Planck scale starting with a low string scale is to have also some larger extra dimensions, where only gravity propagates. In such theories, dimensional reduction generically leads to at least two radion fields, one associated with the total volume of the extra spatial dimensions, and the other with the ratio of the sizes of small and large extra dimensions. In this paper, we discuss the impact of the radion fields on cosmology. We emphasize various aspects of radion physics such as radion coupling to the Standard Model fields, bare and dressed radion masses during inflation, dynamical stabilization of radions during and after inflation, radion decay life time and its late dominance in thermal history of the Universe as well as its quantum fluctuations during inflation. We argue that models where the radion plays the role of an inflaton or the inflaton is a brane scalar field, run into problems. We then present a successful inflation model with bulk scalar fields that seems to have all the desired properties. We also briefly discuss the possibility of radion as a cold dark matter candidate.Comment: 37 pages + 3 figure

75As NMR local probe study of magnetism in (Eu1-xKx)Fe2As2

75As NMR measurements were performed as a function of temperature and doping in (Eu1-xKx)Fe2As2 (x=0,0.38,0.5,0.7) samples. The large Eu2+ moments and their fluctuations are found to dominate the 75As NMR properties. The 75As nuclei close to the Eu2+ moments likely have a very short spin-spin relaxation time (T2) and are wiped out of our measurement window. The 75As nuclei relatively far from Eu2+ moments are probed in this study. Increasing the Eu content progressively decreases the signal intensity with no signal found for the full-Eu sample (x=0). The large 75As NMR linewidth arises from an inhomogeneous magnetic environment around them. The spin lattice relaxation rate (1/T1) for x=0.5 and 0.7 samples is nearly independent of temperature above 100K and results from a coupling to paramagnetic fluctuations of the Eu2+ moments. The behavior of 1/T1 at lower temperatures has contributions from the antiferromagnetic fluctuations of the Eu2+ moments as also the fluctuations intrinsic to the FeAs planes and from superconductivity.Comment: 6 pages, 6 figures (to appear in EPJB

Angular Inflation from Supergravity

We study supergravity inflationary models where inflation is produced along the angular direction. For this we express the scalar component of a chiral superfield in terms of the radial and the angular components. We then express the supergravity potential in a form particularly simple for calculations involving polynomial expressions for the superpotential and Kahler potential. We show for a simple Polonyi model the angular direction may give rise to a stage of inflation when the radial field is fixed to its minimum. We obtain analytical expressions for all the relevant inflationary quantities and discuss the possibility of supersymmetry breaking in the radial direction while inflating by the angular component.Comment: 7 pages, one figure. Final version. Title changed, two figures droppe

Neutral Higgs boson pair production at the LC in the Noncommutative Standard Model

We study the Higgs boson pair production through $e^+e^-$ collision in the noncommutative(NC) extension of the standard model using the Seiberg-Witten maps of this to the first order of the noncommutative parameter $\Theta_{\mu \nu}$. This process is forbidden in the standard model with background space-time being commutative. We find that the cross section of the pair production of Higgs boson (of intermediate and heavy mass) at the future Linear Collider(LC) can be quite significant for the NC scale $\Lambda$ lying in the range $0.5 - 1.0$ TeV. Finally, using the direct experimental(LEP II, Tevatron and global electro-weak fit) bound on Higgs mass, we obtain bounds on the NC scale as 665 GeV $\le \Lambda \le 998$ GeV.Comment: 14 pages, 8 figure

Gauge invariant MSSM inflaton

We argue that all the necessary ingredients for successful inflation are present in the flat directions of the Minimally Supersymmetric Standard Model. We show that out of many gauge invariant combinations of squarks, sleptons and Higgses, there are two directions, ${\bf LLe}$, and ${\bf udd}$, which are promising candidates for the inflaton. The model predicts more than $10^3$ e-foldings with an inflationary scale of $H_{\rm inf}\sim {\cal O}(1-10)$ GeV, provides a tilted spectrum with an amplitude of $\delta_H\sim 10^{-5}$ and a negligible tensor perturbation. The temperature of the thermalized plasma could be as low as $T_{rh}\sim {\cal O}(1-10)$~TeV. Parts of the inflaton potential can be determined independently of cosmology by future particle physics experiments.Comment: 4 revtex pages, some references added, stabilization of moduli and supergravity effects are discusse

Application of importance sampling to the computation of large deviations in non-equilibrium processes

We present an algorithm for finding the probabilities of rare events in nonequilibrium processes. The algorithm consists of evolving the system with a modified dynamics for which the required event occurs more frequently. By keeping track of the relative weight of phase-space trajectories generated by the modified and the original dynamics one can obtain the required probabilities. The algorithm is tested on two model systems of steady-state particle and heat transport where we find a huge improvement from direct simulation methods.Comment: 5 pages, 4 figures; some modification

Coupled Inflation and Brane Gases

We study an effective four-dimensional theory with an action with two scalar fields minimally coupled to gravity, and with a matter action which couples to the two scalar fields via an overall field-dependent coefficient in the action. Such a theory could arise from a dimensional reduction of supergravity coupled to a gas of branes winding the compactified dimensions. We show the existence of solutions corresponding to power-law inflation. The graceful exit from inflation can be obtained by postulating the decay of the branes, as would occur if the branes are unstable in the vacuum and stabilized at high densities by plasma effects. This construction provides an avenue for connecting string gas cosmology and the late-time universe.Comment: 11 page