Neutrino cosmology after WMAP 7-year data and LHC first Z' bounds.

The gauge-extended U(1)(C)×SU(2)(L)×U(1)(I(R))×U(1)(L) model elevates the global symmetries of the standard model (baryon number B and lepton number L) to local gauge symmetries. The U(1)(L) symmetry leads to three superweakly interacting right-handed neutrinos. This also renders a B-L symmetry nonanomalous. The superweak interactions of these Dirac states permit ν(R) decoupling just above the QCD phase transition: 175 is < or approximately equal to T(ν(R))(dec)/MeV is < or approximately equal to 250. In this transitional region, the residual temperature ratio between ν(L) and ν(R) generates extra relativistic degrees of freedom at BBN and at the CMB epochs. Consistency with both WMAP 7-year data and recent estimates of the primordial 4He mass fraction is achieved for 3

Dijet signals for low mass strings at the Large Hadron Collider.

Assuming that the fundamental string mass scale is in the TeV range and the theory is weakly coupled, we discuss possible signals of string physics at the Large Hadron Collider (LHC). In D-brane constructions, the dominant contributions to full-fledged string amplitudes for all the common QCD parton subprocesses leading to dijets are completely independent of the details of compactification, and can be evaluated in a parameter-free manner. We make use of these amplitudes evaluated near the first resonant pole to determine the discovery potential of LHC for the first Regge excitations of the quark and gluon. Remarkably, the reach of LHC after a few years of running can be as high as 6.8 TeV. Even after the first 100 pb(-1) of integrated luminosity, string scales as high as 4.0 TeV can be discovered. Data on pp-->directgamma + jet can provide corroboration for string physics at scales as high as 5 TeV.

Jet signals for low mass strings at the large hadron collider.

The mass scale M{s} of superstring theory is an arbitrary parameter that can be as low as few TeVs if the Universe contains large extra dimensions. We propose a search for the effects of Regge excitations of fundamental strings at the CERN Large Hadron Collider (LHC), in the process pp-->gamma+jet. The underlying parton process is dominantly the single photon production in gluon fusion, gg-->gammag, with open string states propagating in intermediate channels. If the photon mixes with the gauge boson of the baryon number, which is a common feature of D-brane quivers, the amplitude appears already at the string disk level. It is completely determined by the mixing parameter-and it is otherwise model (compactification) independent. Even for relatively small mixing, 100 fb{-1} of LHC data could probe deviations from standard model physics, at a 5sigma significance, for M{s} as large as 3.3 TeV.

Scalar modifications to gravity from unparticle effects may be testable.

Interest has focused recently on low energy implications of a nontrivial scale invariant sector of an effective field theory with an IR fixed point, manifest in terms of "unparticles" with peculiar properties. If unparticle stuff exists it could couple to the stress tensor and mediate a new "fifth" force ("ungravity"). Under the assumption of strict conformal invariance in the hidden sector down to low energies, we compute the lowest order ungravity correction to the Newtonian gravitational potential and find scale invariant power law corrections of type (R_(G)/r)(2d)_(U)(-1), where d_(U) is an anomalous unparticle dimension and R_(G) is a characteristic length scale where the ungravity interactions become significant. It is shown that a discrimination between extra dimension models and ungravity is possible in future improved submillimeter tests of gravity.

TeV gamma rays from photodisintegration and daughter deexcitation of cosmic-ray nuclei.

It is commonly assumed that high-energy gamma rays are made via either purely electromagnetic processes or the hadronic process of pion production, followed by decay. We investigate astrophysical contexts where a third process (A*) would dominate: namely, the photodisintegration of highly boosted nuclei followed by daughter deexcitation. Starburst regions such as Cygnus OB2 appear to be promising sites for TeV gamma-ray emission via this mechanism. A unique feature of the A* process is a sharp flattening of the energy spectrum below approximately 10 TeV/(T/eV) for gamma-ray emission from a thermal region of temperature T. The A* mechanism described herein offers an important contribution to gamma-ray astronomy in the era of intense observational activity.

Particle physics on ice: constraints on neutrino interactions far above the weak scale.

Ultrahigh energy cosmic rays and neutrinos probe energies far above the weak scale. Their usefulness might appear to be limited by astrophysical uncertainties; however, by simultaneously considering up- and down-going events, one may disentangle particle physics from astrophysics. We show that present data from the AMANDA experiment in the South Pole ice already imply an upper bound on neutrino cross sections at energy scales that will likely never be probed at man-made accelerators. The existing data also place an upper limit on the neutrino flux valid for any neutrino cross section. In the future, similar analyses of IceCube data will constrain neutrino properties and fluxes at the theta(10%) level.