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We construct explicitly time-dependent exact solutions to the field equations of 6D gauged chiral supergravity, compactified to 4D in the presence of up to two 3-branes situated within the extra dimensions. The solutions we find are scaling solutions, and are plausibly attractors which represent the late-time evolution of a broad class of initial conditions. By matching their near-brane boundary conditions to physical brane properties we argue that these solutions (together with the known maximally-symmetric solutions and a new class of non-Lorentz-invariant static solutions, which we also present here) describe the bulk geometry between a pair of 3-branes with non-trivial on-brane equations of state., Contribution to the New Journal of Physics focus issue on Dark Energy; 28 pages

We compute (as functions of the shape and Wilson-line moduli) the one-loop Casimir energy induced by higher-dimensional supergravities compactified from 6D to 4D on 2-tori, and on some of their Z_N orbifolds. Detailed calculations are given for a 6D scalar field having an arbitrary 6D mass m, and we show how to extend these results to higher-spin fields for supersymmetric 6D theories. Particular attention is paid to regularization issues and to the identification of the divergences of the potential, as well as the dependence of the result on m, including limits for which m^2 A > 1 where A is the volume of the internal 2 dimensions. Our calculation extends those in the literature to very general boundary conditions for fields about the various cycles of these geometries. The results have potential applications towards Supersymmetric Large Extra Dimensions (SLED) as a theory of the Dark Energy. First, they provide an explicit calculation within which to follow the dependence of the result on the mass of the bulk states which travel within the loop, and for heavy masses these results bear out the more general analysis of the UV-sensitivity obtained using heat-kernel methods. Second, because the potentials we find describe the dynamics of the classical flat directions of these compactifications, within SLED they would describe the present-day dynamics of the Dark Energy.

We explore the implications for neutrino masses and mixings within the minimal version of the supersymmetric large-extra-dimensions scenario (MSLED). This model was proposed in {\tt hep-ph/0404135} to extract the phenomenological implications of the promising recent attempt (in {\tt hep-th/0304256}) to address the cosmological constant problem. Remarkably, we find that the simplest couplings between brane and bulk fermions within this approach can lead to a phenomenologically-viable pattern of neutrino masses and mixings that is also consistent with the supernova bounds which are usually the bane of extra-dimensional neutrino models. Under certain circumstances the MSLED scenario can lead to a lepton mixing (PMNS) matrix close to the so-called bi-maximal or the tri-bimaximal forms (which are known to provide a good description of the neutrino oscillation data). We discuss the implications of MSLED models for neutrino phenomenology., Comment: 38 pages, 1 figure; Reposted with a few additional references

Motivated by the string landscape we examine scenarios for which inflation is a two-step process, with a comparatively short inflationary epoch near the string scale and a longer period at a much lower energy (like the TeV scale). We quantify the number of $e$-foldings of inflation which are required to yield successful inflation within this picture. The constraints are very sensitive to the equation of state during the epoch between the two inflationary periods, as the extra-horizon modes can come back inside the horizon and become reprocessed. We find that the number of $e$-foldings during the first inflationary epoch can be as small as 12, but only if the inter-inflationary period is dominated by a network of cosmic strings (such as might be produced if the initial inflationary period is due to the brane-antibrane mechanism). In this case a further 20 $e$-foldings of inflation would be required at lower energies to solve the late universe's flatness and horizon problems., Comment: 27 pages, 6 figures; v2: refences added

We re-examine the properties of the axially-symmetric solutions to chiral gauged 6D supergravity, recently found in refs. hep-th/0307238 and hep-th/0308064. Ref. hep-th/0307238 finds the most general solutions having two singularities which are maximally-symmetric in the large 4 dimensions and which are axially-symmetric in the internal dimensions. We show that not all of these solutions have purely conical singularities at the brane positions, and that not all singularities can be interpreted as being the bulk geometry sourced by neutral 3-branes. The subset of solutions for which the metric singularities are conical precisely agree with the solutions of ref. hep-th/0308064. Establishing this connection between the solutions of these two references resolves a minor conflict concerning whether or not the tensions of the resulting branes must be negative. The tensions can be both negative and positive depending on the choice of parameters. We discuss the physical interpretation of the non-conical solutions, including their significance for the proposal for using 6-dimensional self-tuning to understand the small size of the observed vacuum energy. In passing we briefly comment on a recent paper by Garriga and Porrati which criticizes the realization of self-tuning in 6D supergravity., Comment: 27 pages, 1 figure; JHEP3 style; Some references added, and discussion of tension constraints and unwarped solutions made more explicit

Both inflationary and quintessence cosmologies require scalar fields which roll very slowly over cosmological time scales, and so typically demand extremely flat potentials. Sufficiently flat potentials are notoriously difficult to obtain from realistic theories of microscopic physics, and this poses a naturalness problem for both types of cosmologies. We propose a brane-world-based microscopic mechanism for generating scalar potentials which can naturally be flat enough for both types of cosmological applications. The scalars of interest are higher-dimensional bulk pseudo-Goldstone bosons whose scale of symmetry breaking is exponentially suppressed in the higher-dimensional theory by the separation between various branes. The light scalars appear in the effective 4D theory as pseudo-Goldstone bosons. Since naturalness problems are more severe for quintessence models, motivated by our construction we explore in more detail the possibilities for using pseudo-Goldstone bosons to build quintessence models. Depending on how the cosmological constant problem is solved, these models typically imply the universe is now entering a matter-dominated oscillatory phase for which the equation of state parameter w = p/rho oscillates between w = 1 and w = -1., 27 pages, LaTeX, 5 figures using epsfig, uses JHEP3

We investigate the possible influence of very-high-energy physics on inflationary predictions focussing on whether effective field theories can allow effects which are parametrically larger than order H^2/M^2, where M is the scale of heavy physics and H is the Hubble scale at horizon exit. By investigating supersymmetric hybrid inflation models, we show that decoupling does not preclude heavy-physics having effects for the CMB with observable size even if H^2/M^2 << O(1%), although their presence can only be inferred from observations given some a priori assumptions about the inflationary mechanism. Our analysis differs from the results of hep-th/0210233, in which other kinds of heavy-physics effects were found which could alter inflationary predictions for CMB fluctuations, inasmuch as the heavy-physics can be integrated out here to produce an effective field theory description of low-energy physics. We argue, as in hep-th/0210233, that the potential presence of heavy-physics effects in the CMB does not alter the predictions of inflation for generic models, but does make the search for deviations from standard predictions worthwhile., 19 pages, LaTeX, no figures, uses JHEP3

We present warped compactification solutions of six-dimensional supergravity, which are generalizations of the Randall-Sundrum warped brane world to codimension two and to a supersymmetric context. In these solutions the dilaton varies over the extra dimensions, and this makes the electroweak hierarchy only power-law sensitive to the proper radius of the extra dimensions (as opposed to being exponentially sensitive as in the RS model). Warping changes the phenomenology of these models because the Kaluza-Klein gap can be much larger than the internal space's inverse proper radius. We provide examples both for Romans' nonchiral supergravity and Salam-Sezgin chiral supergravity, and in both cases the solutions break all of the supersymmetries of the models. We interpret the solution as describing the fields sourced by a 3-brane and a boundary 4-brane (Romans' supergravity) or by one or two 3-branes (Salam-Sezgin supergravity), and we identify the topological constraints which are required by this interpretation. For both types of solutions the 3-branes are flat for all topologically-allowed values of the brane tensions. We identify the general mechanism for and limitations of the self-tuning of the effective 4D cosmological constant in higher-dimensional supergravity which these models illustrate., Comment: 47 pages, 2 figures; added references

For a light enough Higgs boson, the effective potential of the Standard Model develops a dangerous instability at some high energy scale, Lambda, signalling the need for new physics below that scale. On the other hand, a typical low-energy remnant of new physics at some heavy scale, M, is the presence of effective non-renormalizable operators (NROs), suppressed by powers of 1/M. It has been claimed that such operators may modify the behaviour of the effective potential, in such a way as to significantly lower the instability scale. We critically reanalyze the interplay between non-renormalizable operators and vacuum instabilities and find that, contrary to these claims, the effect of NROs on instability bounds is generically small whenever it can be reliably computed., Comment: 17 pages, LaTeX, 3 ps figures

We set up the Polyakov path integral formalism for the open and unoriented bosonic string at tree and one-loop level of string perturbation theory. The relevant Teichmuller parameters, conformal Killing vectors, “large” diffeomorphisms, and functional determinants are given explicitly. As a toy application the one-loop vacuum energy for the open and closed sectors of the unoriented bosonic string is computed.

String theory is spacetimes with boundaries is shown to be equivalent, in some instances, to string theory or orbifolds. This equivalence is used to calculate the Casimir energy of the string between two infinite parallel plates in spacetime. The calculation mimics some features of string theory in Rindler and Schwarzschild spacetimes and supports the conjecture that string theories avoid the singularity problem by giving particle production rates that diverge in the presence of large, but finite, fields.

A classical wormhole solution is constructed for gravity couples to a positive energg, maplese scalar field. We examine carefully the definitions of euclideanization, and find that this solution is equivalent to the wormhole previously obtained for gravity coupled to an antisymmetric, two-index gauge potential, which is locally dual to the scalar field. However, as we explain, this wormhole solution is characterized by a scalar field configuration which is co.

The propagation of bosonic open strings in the presence of background electric fields is examined. For neutral strings (for which the charges on the ends are equal and opposite) in weak fields the string polarizes, altering its spectrum. Above a critical value of the electric field, qEc = T, a classical instability develops in which those transverse string modes that oscillate parallel to the field develop negative squared-masses. For strings with overall charge, the dominant instability in weak fields consists of pair-production, at a constant rate per unit volume, until the classical instability is reached at the critical field, Ec. Although it is in th regime for which the classical instability dominates, it is noteworthy that (modulo tachyons) the pair-production rate goes to zero for infinite fields.

The one-loop divergences in scattering amplitudes involving an arbitrary number of external gravitons, dilatons and gauge bosons are exhibited and shown to cancel in the the type I superstring with gauge group O(32). The analysis is performed in the Polyakov path integral approach in which the divergences can be clearly identified.

We have computed, in detail, the energy and angular distribution of the leptons (l) produced by the decay of winos (W-tilde) via the reaction e/sup +/e/sup -/ ..-->.. W-tilde/sup +/ + W-tilde/sup -/ ..-->.. l/sup +/nu..gamma..-tilde + l/sup -/anti nu..gamma..-tilde within the framework of a supergravity electroweak model. We have also computed the backgrounds to this reaction from the production and subsequent decays of tau/sup +/tau/sup -/ pairs or pairs of new sequential heavy leptons. We conclude that it is possible to distinguish the wino from an ordinary heavy lepton and, moreover, that winos lighter than the W-boson would be clearly identifiable at LEP energies. 22 refs., 3 figs.

We construct the low-energy D = 4, N = 1 supergravity that arises in superstring theories for an arbitrary number of generations. The couplings of all massless modes that carry low-energy gauge quantum numbers are calculated by truncating the heavy Kaluza-Klein modes of the ten-dimensional effective field theory. The resulting action is compared to the most general effective action compatible with the symmetries of the underlying ten-dimensional field (and string) theories. This comparison indicates which features of the truncation correctly approximate the exact low-energy action.

The off-shell relationship between three-form field strengths and massless scalar fields is re-investigated, with particular attention paid to the boundary conditions in the path integral. The two theories are shown to be not completely equivalent, in agreement with earlier work. It is shown, in particular, that eigenstates of the “magnetic” part, Hijk, of the three-form field dualize to eigenstates of the canonical momentum, adot, of the scalar field. This correspondence is just what is required for the consistency of the dualization of the Giddings-Strominger wormhole to scalar field theory.

We set up the Polyakov path integral formalism for the type-I superstring at tree and one-loop level of string perturbation theory. The relevant super-Teichmuller parameters, conformal Killing spinors, and functional determinants are given explicitly. As an application the one-loop vacuum energy for the open superstring is computed and shown to vanish for the torus, Klein bottle, cylinder and Mobius strip separately.

Discrepancies between measurements of and theoretical predictions for the orbital precession in binary-star systems are reexamined assuming the existence of a hitherto undiscovered, very weak long-range force. The binary-star data are consistent with the existence of such a force only if the internal density parameter ${k}_{2}$, computed using stellar models, is uncertain to 80% for some of the stars involved. If so, the observations are compatible with a repulsive force that couples to electrically neutral bulk matter through a linear combination of neutron and proton number with ${10}^{\mathrm{\ensuremath{-}}5}$--${10}^{\mathrm{\ensuremath{-}}4}$ the strength of gravity and a range of (3--6)\ifmmode\times\else\texttimes\fi{}${10}^{6}$ km. Surprisingly, such a force is consistent with the binary pulsar and extraterrestrial solar-system tests of general relativity. It is ruled out only by very recent tests of the principle of equivalence on Earth. Such binary-star systems are extremely sensitive to, and so furnish strong constraints on, new forces.

We update the best constraints on fluctuations in the solar medium deep within the solar Radiative Zone to include the new SNO-salt solar neutrino measurements. We find that these new measurements are now sufficiently precise that neutrino oscillation parameters can be inferred independently of any assumptions about fluctuation properties. Constraints on fluctuations are also improved, with amplitudes of 5% now excluded at the 99% confidence level for correlation lengths in the range of several hundred km. Because they are sensitive to correlation lengths which are so short, these solar neutrino results are complementary to constraints coming from helioseismology., Comment: 4 pages, LaTeX file using RevTEX4, 6 figures included

We construct time-dependent S-brane solutions to the supergravity field equations in various dimensions which (unlike most such geometries) do not contain curvature singularities. The configurations we consider are less symmetric than are earlier solutions, with our simplest solution being obtained by a simple analytical continuation of the Kerr geometry. We discuss in detail the global structure and properties of this background. We then generalize it to higher dimensions and to include more complicated field configurations - like non vanishing scalars and antisymmetric tensor gauge potentials - by the usual artifice of applying duality symmetries., 22 pages, 3 figures. Typos in eq.(2.6) corrected

The 100+ free parameters of the minimal supersymmetric standard model (MSSM) make it computationally difficult to compare systematically with data, motivating the study of specific parameter reductions such as the cMSSM and pMSSM. Here we instead study the reductions of parameter space implied by using minimal flavour violation (MFV) to organise the R-parity conserving MSSM, with a view towards systematically building in constraints on flavour-violating physics. Within this framework the space of parameters is reduced by expanding soft supersymmetry-breaking terms in powers of the Cabibbo angle, leading to a 24-, 30- or 42-parameter framework (which we call MSSM-24, MSSM-30, and MSSM-42 respectively), depending on the order kept in the expansion. We provide a Bayesian global fit to data of the MSSM-30 parameter set to show that this is manageable with current tools. We compare the MFV reductions to the 19-parameter pMSSM choice and show that the pMSSM is not contained as a subset. The MSSM-30 analysis favours a relatively lighter TeV-scale pseudoscalar Higgs boson and $\tan \beta \sim 10$ with multi-TeV sparticles., Comment: 2nd version, minor comments and references added, accepted for publication in JHEP

We rebut the recent claim (arXiv:0912.5463) that Einstein-frame scattering in the Higgs inflation model is unitary above the cut-off energy Lambda ~ Mp/xi. We show explicitly how unitarity problems arise in both the Einstein and Jordan frames of the theory. In a covariant gauge they arise from non-minimal Higgs self-couplings, which cannot be removed by field redefinitions because the target space is not flat. In unitary gauge, where there is only a single scalar which can be redefined to achieve canonical kinetic terms, the unitarity problems arise through non-minimal Higgs-gauge couplings.