Highly supercritical strings ($c\gg 15$) with a timelike linear dilaton provide a large class of solutions to string theory, in which closed string tachyon condensation is under control (and follows the world sheet renormalization group flow). In this note we analyze the late-time stability of such backgrounds, including transitions between them. The large friction introduced by the rolling dilaton and the rapid decrease of the string coupling suppress the backreaction of naive instabilities. In particular, although the graviton, dilaton, and other light fields have negative effective mass squared in the linear dilaton background, the decaying string coupling ensures that their condensation does not cause large backreaction. Similarly, the copious particles produced in transitions between highly supercritical theories do not back-react significantly on the solution. We discuss these features also in a somewhat more general class of time-dependent backgrounds with stable late-time asymptotics.

We show that the neutrino models, as suggested by Low [1], which have an additional Abelian family symmetry and a real Higgs singlet to the default see-saw do not hinder the possibility of successful thermal leptogenesis. For these models (neglecting radiative effects), we have investigated the situation of strong washout in both the one-flavor approximation and when flavor effects are included. The result is that while such models predict that ${\theta }_{13}=0$ and that one light neutrino to be massless, they do not modify or provide significant constraints on the typical leptogenesis scenario where the final asymmetry is dominated by the decays of the lightest right-handed neutrinos.

We show that positive averaged acceleration $a_D$ obtained in Lemaitre-Tolman-Bondi (LTB) models through spatial averaging can require integration over a region beyond the event horizon of the central observer. We provide an example of a LTB model with positive $a_D$ in which the luminosity distance $D_L(z)$ does not contain information about the entire spatially averaged region, making $a_D$ unobservable. Since the cosmic acceleration $a^{\mathrm{FRW}}$ is obtained from fitting the observed luminosity distance to a Friedmann-Robertson-Walker (FRW) model we conclude that in general a positive $a_D$ in LTB models does not imply a positive $a^{\mathrm{FRW}}$.

Extensions of the standard model with low-energy supersymmetry generically allow baryon- and lepton-number violating operators of dimension four and five, yielding rapid proton decay. The dimension-four operators are usually forbidden by matter parity. We investigate to what extent the appearance of dimension-five operators at the Planck scale may be constrained by the different grand-unified gauge groups. Dimension-five operators are suppressed in models based on ${\mathrm{E}}_6$ and ${\mathrm{SU}(3)}_C\times {\mathrm{SU}(3)}_L\times {\mathrm{SU}(3)}_R$, where four matter fields do not form a gauge singlet. An intermediate scale offers the possibility to sufficiently suppress these dimension-five operators.

The minimal extension of the scalar sector of the standard model contains an additional real scalar field with no gauge quantum numbers. Such a field does not couple to the quarks and leptons directly but rather through its mixing with the standard model Higgs field. We examine the phenomenology of this model focusing on the region of parameter space where the new scalar particle is significantly lighter than the usual Higgs scalar and has small mixing with it. In this region of parameter space most of the properties of the additional scalar particle are independent of the details of the scalar potential. Furthermore the properties of the scalar that is mostly the standard model Higgs can be drastically modified since its dominant branching ratio may be to a pair of the new lighter scalars.

Motivated by the absence, so far, of any direct signal of conventional low-energy supersymmetry, we explore the consequences of making the lightest Higgs boson in supersymmetry relatively heavy, up to about 300 GeV, in the most straightforward way, i.e. via the introduction of a chiral singlet $S$ with a superpotential interaction with the Higgs doublets, $\lambda S{H}_1{H}_2$. The coupling $\lambda$ dominates over all the other couplings and, to maintain the successful perturbative analysis of the electroweak precision tests, is only restricted to remain perturbative up to about 10 TeV. The general features of this “$\lambda \mathrm{SUSY}$” framework, which deviates significantly from the minimal supersymmetric standard model or the standard next to minimal supersymmetric standard model, are analyzed in different areas: electroweak precision tests, dark matter, naturalness bounds on superparticle masses, and LHC signals. There is a rich Higgs/Higgsino sector in the (200–700) GeV mass region, which may include LSP Higgsino dark matter. All other superpartners, apart from the top squarks, may naturally be heavier than 1–2 TeV.

The results of a new search for positronium decays into invisible final states are reported. Convincing detection of this decay mode would be a strong evidence for new physics beyond the standard model (SM): for example, the existence of extra–dimensions, of milli-charged particles, of new light gauge bosons or of mirror particles. Mirror matter could be a relevant dark matter candidate. In this paper the setup and the results of a new experiment are presented. In a collected sample of about $(6.31\pm 0.28)\times {10}^6$ orthopositronium decays, no evidence for invisible decays in an energy [0,80] keV was found and an upper limit on the branching ratio of orthopositronium $\mathrm{o}\mathrm{\text{−}}\mathrm{Ps}\to \mathrm{\text{invisible}}$ could be set: $\mathrm{Br}(\mathrm{o}\mathrm{\text{−}}\mathrm{Ps}\to \mathrm{\text{invisible}})<4.2\times {10}^{-7}(90\%\mathrm{C}.\mathrm{L}.)$ Our results provide a limit on the photon mirror-photon mixing strength $ϵ\le 1.55\times {10}^{-7}(90\%\mathrm{C}.\mathrm{L}.)$ and rule out particles lighter than the electron mass with a fraction $Q_x\le 3.4\times {10}^{-5}$ of the electron charge. Furthermore, upper limits on the branching ratios for the decay of parapositronium $\mathrm{Br}(\mathrm{p}\mathrm{\text{−}}\mathrm{Ps}\to \mathrm{\text{invisible}})\le 4.3\times {10}^{-7}(90\%\mathrm{C}.\mathrm{L}.)$ and the direct annihilation $\mathrm{Br}(e^{+}{e}^{-}\to \mathrm{\text{invisible}})\le 2.1\times {10}^{-8}(90\%\mathrm{C}.\mathrm{L}.)$ could be set.

We elaborate on the role of quantum statistics in twisted Poincaré invariant theories. It is shown that, in order to have twisted Poincaré group as the symmetry of a quantum theory, statistics must be twisted. It is also confirmed that the removal of UV-IR mixing (in the absence of gauge fields) in such theories is a natural consequence.

A self-consistent effective field theory of modified gravity has recently been proposed with spontaneous breaking of local Lorentz invariance. The symmetry is broken by a vector field with the wrong-sign mass term and it has been shown to have additional graviton modes and modified dispersion relations. In this paper we study the evolution of a homogeneous and isotropic universe in the presence of such a vector field with a minimum lying along the timelike direction. A plethora of different regimes is identified, such as accelerated expansion, loitering, collapse, and tracking.

This paper investigates evolution of cosmic structures in different environments. For this purpose the quasispherical Szekeres model is employed. The Szekeres model is an exact solution of the Einstein field equations within which it is possible to describe more than one structure. In this way investigations of the evolution of the cosmic structures presented here can be freed from such assumptions as a small value of the density contrast. Also, studying the evolution of two or three structures within one framework enables us to follow the interaction between these structures and their impact on the evolution. Main findings include a conclusion that small voids surrounded by large overdensities evolve slower than large, isolated voids do. On the other hand, large voids enhance the evolution of adjacent galaxy superclusters which evolve much faster than isolated superclusters.

If there was a first-order phase transition in the early universe, there should be an associated stochastic background of gravitational waves. In this paper, we point out that the characteristic frequency of the spectrum due to phase transitions which took place in the temperature range $100\mathrm{GeV}–{10}^7\mathrm{GeV}$ is precisely in the window that will be probed by the second generation of space-based interferometers such as the big bang observer (BBO). Taking into account the astrophysical foreground, we determine the type of phase transitions which could be detected either at LISA, LIGO or BBO, in terms of the amount of supercooling and the duration of the phase transition that are needed. Those two quantities can be calculated for any given effective scalar potential describing the phase transition. In particular, the new models of electroweak symmetry-breaking which have been proposed in the last few years typically have a different Higgs potential from the standard model. They could lead to a gravitational wave signature in the milli-Hertz frequency, which is precisely the peak sensitivity of LISA. We also show that the signal coming from phase transitions taking place at $T\sim 1–100\mathrm{TeV}$ could entirely screen the relic gravitational wave signal expected from standard inflationary models.

Using the “modified DPMJET-III” model explained in the previous paper [T. Sanuki et al., preceding Article, Phys. Rev. D 75, 043005 (2007).], we calculate the atmospheric neutrino flux. The calculation scheme is almost the same as HKKM04 [M. Honda, T. Kajita, K. Kasahara, and S. Midorikawa, Phys. Rev. D 70, 043008 (2004).], but the usage of the “virtual detector” is improved to reduce the error due to it. Then we study the uncertainty of the calculated atmospheric neutrino flux summarizing the uncertainties of individual components of the simulation. The uncertainty of $K$-production in the interaction model is estimated using other interaction models: FLUKA’97 and FRITIOF 7.02, and modifying them so that they also reproduce the atmospheric muon flux data correctly. The uncertainties of the flux ratio and zenith angle dependence of the atmospheric neutrino flux are also studied.

We have studied the hadronic interaction for the calculation of the atmospheric neutrino flux by summarizing the accurately measured atmospheric muon flux data and comparing with simulations. We find the atmospheric muon and neutrino fluxes respond to errors in the $\pi$-production of the hadronic interaction similarly, and compare the atmospheric muon flux calculated using the HKKM04 [M. Honda, T. Kajita, K. Kasahara, and S. Midorikawa, Phys. Rev. D 70, 043008 (2004).] code with experimental measurements. The ${\mu }^{+}+{\mu }^{-}$ data show good agreement in the $1\sim 30\mathrm{GeV}/c$ range, but a large disagreement above $30\mathrm{GeV}/c$. The ${\mu }^{+}/{\mu }^{-}$ ratio shows sizable differences at lower and higher momenta for opposite directions. As the disagreements are considered to be due to assumptions in the hadronic interaction model, we try to improve it phenomenologically based on the quark parton model. The improved interaction model reproduces the observed muon flux data well. The calculation of the atmospheric neutrino flux will be reported in the following paper [M. Honda et al., Phys. Rev. D 75, 043006 (2007).].

We have measured surface-force noise on a hollow replica of a LISA proof mass surrounded by its capacitive motion sensor. Forces are detected through the torque exerted on the proof mass by means of a torsion pendulum in the 0.1–30 mHz range. The sensor and electronics have the same design as for the flight hardware, including 4 mm gaps around the proof mass. The measured upper limit for forces would allow detection of a number of galactic binaries signals with signal-to-noise ratio up to $\approx 40$ for 1 yr integration. We also discuss how LISA Pathfinder will substantially improve this limit, approaching the LISA performance.

We study the simplest generic extension of the standard model which allows for conventional electroweak baryogenesis, through the addition of dimension-six operators in the Higgs sector. At least one such operator is required to be $CP$-odd, and we study the constraints on such a minimal setup, and related scenarios with minimal flavor violation, from the null results of searches for electric dipole moments (EDMs), utilizing the full set of two-loop contributions to the EDMs. The results indicate that the current bounds are stringent, particularly that of the recently updated neutron EDM, but fall short of ruling out these scenarios. The next generation of EDM experiments should be sufficiently sensitive to provide a conclusive test.

In supersymmetric theories where the lightest supersymmetric particle is the gravitino the next to lightest supersymmetric particle is typically a long-lived charged slepton. In this paper, following our earlier proposal [I. Albuquerque, G. Burdman, and Z. Chacko, Phys. Rev. Lett. 92, 221802 (2004).], we perform a detailed study of the production of pairs of these particles induced by the interactions of high energy cosmic neutrinos with nucleons in the Earth, their propagation through the Earth, and finally their detection in neutrino telescopes. We investigate the charged slepton energy loss in detail and establish that the relatively small cross section for the production of supersymmetric particles is partially compensated for by the very long range of these heavy particles. The signal, consisting of two parallel charged tracks emerging from the Earth, is characterized by a track separation of a few hundred meters. We perform a careful analysis of the main background, coming from direct di-muon production, and show that it can be separated from the signal due to its characteristically smaller track separation. We conclude that neutrino telescopes will complement collider searches in the determination of the supersymmetry breaking scale, and may even provide the first evidence for supersymmetry at the weak scale.

Stochastic processes described by evolution equations in the universality class of the Fisher-Kolmogorov-Petrovsky-Piscounov equation may be approximately factorized into a linear stochastic part and a nonlinear deterministic part. We prove this factorization on a model with no spatial dimensions and we illustrate it numerically on a one-dimensional toy model that possesses some of the main features of high energy QCD evolution. We explain how this procedure may be applied to QCD amplitudes, by combining Salam’s Monte Carlo implementation of the dipole model and a numerical solution of the Balitsky-Kovchegov equation.

In the context of neutrino factories, we review the solution of the degeneracies in the neutrino oscillation parameters. In particular, we have set limits to ${sin}^{2}2{\theta }_{13}$ in order to accomplish the unambiguous determination of ${\theta }_{23}$ and $\delta$. We have performed two different analysis. In the first, at a baseline of 3000 km, we simulate a measurement of the channels ${\nu }_e\to {\nu }_{\mu }$, ${\nu }_e\to {\nu }_{\tau }$, and ${\overline{\nu }}_{\mu }\to {\overline{\nu }}_{\mu }$, combined with their respective conjugate ones, with a muon energy of 50 GeV and a running time of five years. In the second, we merge the simulated data obtained at $L=3000\mathrm{km}$ with the measurement of ${\nu }_e\to {\nu }_{\mu }$ channel at 7250 km, the so-called “magic baseline.” In both cases, we have studied the impact of varying the ${\nu }_{\tau }$ detector efficiency-mass product, $({ϵ}_{{\nu }_{\tau }}\times M_{\tau })$, at 3000 km, keeping unchanged the ${\nu }_{\mu }$ detector mass and its efficiency. At $L=3000\mathrm{km}$, we found the existence of degenerate zones, that correspond to values of ${\theta }_{13}$, which are equal or almost equal to the true ones. These zones are extremely difficult to discard, even when we increase the number of events. However, in the second scenario, this difficulty is overcome, demonstrating the relevance of the “magic baseline.” From this scenario, the best limits of ${sin}^{2}2{\theta }_{13}$, reached at $3\sigma$, for ${sin}^{2}2{\theta }_{23}=0.95$, 0.975, and 0.99 are: 0.008, 0.015, and 0.045, respectively, obtained at $\delta =0$, and considering $({ϵ}_{{\nu }_{\tau }}\times M_{\tau })\approx 125$, which is 5 times the initial efficiency-mass combination.