Physical Review D

We present measurements of the CP-violation parameters S and C for the radiative decay B⁰→ηK_S⁰γ; for B→ηKγ we also measure the branching fractions and for B⁺→ηK⁺γ the time-integrated charge asymmetry A_ch. The data, collected with the BABAR detector at the Stanford Linear Accelerator Cent...

Data collected in run II of the Fermilab Tevatron are searched for indications of new electroweak-scale physics. Rather than focusing on particular new physics scenarios, CDF data are analyzed for discrepancies with the standard model prediction. A model-independent approach (Vista) considers gross...

Starting from a new zeroth order basis for quark mixing (CKM) matrix based on the quark-lepton complementarity and the tribimaximal pattern of lepton mixing, we derive a triminimal parametrization of a CKM matrix with three small angles and a CP-violating phase as its parameters. This new triminimal...

It is generally believed that neutrino mass hierarchy can be determined at a long baseline experiment, often using accelerator neutrino beams. Reactor neutrino experiments at an intermediate baseline have the capability to distinguish normal or inverted hierarchy. Recently, it has been demonstrated ...

Using isospin relations, we predict the standard model correlation between S_π⁰KS≡(sin⁡2β)_π⁰KS and A_π⁰KS, the mixing-induced and direct CP asymmetries of B⁰→π⁰K_S. The calculation uses flavor SU(3) only to fix the isospin-3/2 amplitude through the B^±→π^±π⁰ branching ratio, and thus has...

We report on a search for the decay B⁰→ρ⁰ρ⁰ and other charmless modes with a π⁺π^-π⁺π^- final state, including B⁰→ρ⁰π⁺π^-, nonresonant B⁰→4π^±, B⁰→ρ⁰f₀(980), B⁰→f₀(980)f₀(980) and B⁰→f₀(980)π⁺π^-. These results are obtained from a data sample containing 657×10⁶ BB̅ pa...

We present the first measurement of σ(gg→tt̅ )/σ(pp̅ →tt̅ ). We use 0.96  fb^-1 of sqrt[s] =1.96  TeV pp̅ collision data recorded with the CDF II detector at Fermilab. Using charged particles with low transverse momentum in tt̅ events, we f...

The properties of the dark matter that determine its thermal relic abundance can be very different from the dark matter properties today. We investigate this possibility by coupling a dark matter sector to a scalar that undergoes a phase transition after the dark matter freezes out. If the value of ...

We present a measurement of the branching fraction for the Cabibbo- and color-suppressed B⁰→χ_c1π⁰ decay based on a data sample of 657×10⁶BB̅ events collected at the Υ(4S) resonance with the Belle detector at the KEKB asymmetric-energy e⁺e^- collider. We observe a signal of 40±9 event...

Using a data sample of 24.5×10⁶ ψ(2S) the reactions ψ(2S)→γχ_cJ, χ_cJ→γγ have been studied for the first time to determine the two-photon widths of the χ_cJ states of charmonium in their decay into two photons. The measured quantities are B(ψ(2S)→γχ_c0)×B(χ_c0→γγ)=(2.17±0.32±0.1...

We report a search for the decays B^-→K⁺π^-π^- and B^-→K^-K^-π⁺, which are highly suppressed in the standard model. Using a sample of (467±5)×10⁶ BB̅ pairs collected with the BABAR detector, we do not see any evidence of these decays and determine 90% confidence level upper limits of B(...

Analyzing Υ(nS) decays acquired with the CLEO detector operating at the CESR e⁺e^- collider, we measure for the first time the product branching fractions B[Υ(nS)→γχ_bJ((n-1)P)]B[χ_bJ(n-1)P)→X_i] for n=2 and 3, where X_i denotes, for each i, one of the 14 exclusive light-hadron final states for ...

We present the observation of the decay B⁰→χ_c0K^*0 as well as evidence of B⁺→χ_c0K^*+, with an 8.9 and a 3.6 standard deviation significance, respectively, using a data sample of 454×10⁶ Υ(4S)→BB̅ decays collected with the BABAR detector at the PEP-II B meson factory located at the ...

We examine the spatial density within extended objects of the momentum component p⁺, and find relativistically exact connections to Fourier transforms of gravitational form factors. We apply these results to obtain semiempirical momentum density distributions within nucleons, and similar distributio...

The reasonableness of the use of perturbative QCD notions in the region close to the scale of hadronization, i.e., below ≲1  GeV is under study. First, the interplay between higher orders of pQCD expansion and higher-twist contributions in the analysis of recent Jefferson Lab (JLab) data on th...

We report a study of the suppressed B meson decay B^-→DK^- followed by D→K⁺π^-, where D indicates a D⁰ or D̅ ⁰ state. The two decay paths interfere and provide information on the CP-violating angle ϕ₃. We use a data sample containing 657×10⁶ BB̅ pairs recorded at the Υ(4S) re...

We consider QCD at temperatures T near T_c, where the theory deconfines. We distinguish between a “complete” quark-gluon plasma (QGP), where the vacuum expectation value of the renormalized Polyakov loop is near unity, essentially constant with T, and the “semi”-QGP, where the loop changes st...

We study B⁰→ρ⁰ρ⁰ decays in a sample of 465×10⁶ Υ(4S)→BB̅ events collected with the BABAR detector at the PEP-II asymmetric-energy e⁺e^- collider located at the Stanford Linear Accelerator Center (SLAC). We measure the branching fraction B=(0.92±0.32±0.14)×10^-6 and longitudinal po...

We report the first observation of e⁺e^-→ρ⁺ρ^-, in a data sample of 379  fb^-1 collected with the BABAR detector at the PEP-II e⁺e^- storage ring at center-of-mass energies near sqrt[s] =10.58  GeV. We measure a cross section of σ(e⁺e^-→ρ⁺ρ^-)=8.3±0.7(stat)±0.8(syst)  fb within the ...

For an unsteady baryonic gamma-ray burst (GRB) outflow, the fast and slow proton shells collide with each other and produce energetic soft gamma-ray emission. If the outflow has a significant neutron component, the ultrarelativistic neutrons initially expand freely until decaying at a larger radius....

Near the horizon of a black brane solution in anti-de Sitter space, the long-wavelength fluctuations of the metric exhibit hydrodynamic behavior. For Einstein’s theory, the ratio of the shear viscosity of near-horizon metric fluctuations η to the entropy per unit of transverse volume s is η/s=1...

We derive the equations of motion of test bodies for a theory with nonminimal coupling by means of a multipole method. The propagation equations for pole-dipole particles are worked out for a gravity theory with a very general coupling between the curvature scalar and the matter fields. Our results ...

We investigate neutrino emission from gamma-ray bursts (GRBs) under alternative scenarios for prompt emission (the photospheric and synchrotron self-Compton scenarios) rather than the classical optically thin synchrotron scenario. In the former scenario, we find that neutrinos from the pp reaction c...

The static, i.e., linear momentum independent, part of the next-to-leading order (NLO) gravitational spin(1)-spin(1) interaction Hamiltonian within the post-Newtonian (PN) approximation is calculated from a three-dimensional covariant ansatz for the Hamilton constraint. All coefficients in this ansa...

We consider the conditions for integrating out heavy chiral fields and moduli in N=1 supergravity, subject to two explicit requirements. First, the expectation values of the heavy fields should be unaffected by low energy phenomena. Second, the low energy effective action should be described by N=1 ...

Greybody factors in black-hole physics modify the naive Planckian spectrum that is predicted for Hawking radiation when working in the limit of geometrical optics. We consider the Schwarzschild geometry in (3+1) dimensions, and analyze the Regge-Wheeler equation for arbitrary particle spin s and wav...

One of the goals of NASA’s Fermi Gamma-ray Space Telescope (formerly GLAST) will be the detection of gamma rays from dark-matter annihilation in the Galactic halo. Theoretical arguments suggest that dark matter may be bound into subhalos with masses as small as 10^-4–10²M_⊕. If so, it may be pos...

We study nonaxisymmetric collision of two black holes (BHs) with a high velocity v=|dxⁱ/dx⁰|=   0.6c–0.9c at infinity, where x^μ denotes four-dimensional coordinates. We prepare two boosted BHs for the initial condition which is different from that computed by a simple moving-puncture approac...

We show that nonpertubative lattice studies of four-dimensional N=4 super-Yang-Mills are within reach. We use Ginsparg-Wilson fermions to avoid gluino masses and an exact implementation of the (chiral) R-symmetry, which greatly limits the number of counterterms that must be fine-tuned. Only bosonic ...

We revisit here the recent proposal for overspinning a nearly extreme black hole by means of a quantum tunneling process. We show that electrically neutral massless fermions evade possible backreaction effects related to superradiance, confirming the view that it would be indeed possible to form a n...

The analytic form of the asymptotic behavior of the S matrix in the saturation regime including the running coupling is obtained. To get this result, we solve the Balitsky and Kovchegov-Weigert evolution equations in the saturation regime, which include running coupling corrections. We study also th...

We present a proposal for performing model-independent jets plus missing energy searches. Currently, these searches are optimized for mSUGRA and are consequently not sensitive to all kinematically accessible regions of parameter space. We show that the reach of these searches can be broadened by set...

We present measurements of the CP-violation parameters S and C for the radiative decay B⁰→ηK_S⁰γ; for B→ηKγ we also measure the branching fractions and for B⁺→ηK⁺γ the time-integrated charge asymmetry A_ch. The data, collected with the BABAR detector at the Stanford Linear Accelerator Cent...

Semileptonic B̅ decays to DXℓν̅ (ℓ=e or μ) are selected by reconstructing D⁰ℓ and D⁺ℓ combinations from a sample of 230×10⁶ Υ(4S)→BB̅ decays recorded with the BABAR detector at the PEP-II e⁺e^- collider at SLAC. A global fit to these samples in a three-dime...

We investigate the possibility of generating neutrino masses in the context of split supersymmetric scenarios where all sfermions are very heavy. All relevant contributions coming from the R-parity violating terms to the neutrino mass matrix up to one-loop level are computed showing the importance o...

The up- and down-quark masses are determined from an optimized QCD finite-energy sum rule involving the correlator of axial-vector divergences, to five-loop order in perturbative QCD, and including leading nonperturbative QCD and higher order quark-mass corrections. This finite-energy sum rule is de...

Exclusive photoproduction of dileptons, γN→ℓ⁺ℓ^-N, is and will be measured in ultraperipheral collisions at hadron colliders, such as the Tevatron, Relativistic Heavy Ion Collider, and the LHC. We demonstrate that the timelike deeply virtual Compton scattering mechanism γq→ℓ⁺ℓ^-q where t...

We present a new model, based on color rearrangements, which at the same time can describe both hidden and open charm production in B-meson decays. The model is successfully compared to both inclusive decays, such as B→J/ψX and B→D_sX, as well as exclusive ones, such as B→J/ψK^(*) and B→D^(*)...

In this work we study the predominantly orbital and radial excitations of hadrons containing a single heavy quark. We present meson and baryon mass splittings and ratios of meson decay constants (e.g., f_Bs/f_B and f_Bs^′/f_Bs) resulting from quenched and dynamical two-flavor configurations. Light quar...

A numerical approach is considered for spherically symmetric spacetimes that generalize Lemaître–Tolman–Bondi dust solutions to nonzero pressure (“LTB spacetimes”). We introduce quasilocal (QL) variables that are covariant LTB objects satisfying evolution equations of Friedman–Lemaîtreâ€...

In this paper, the dynamical attractor and heteroclinic orbit have been employed to make the late-time behaviors of the model insensitive to the initial condition and thus alleviate the fine-tuning problem in the torsion cosmology. The late-time de Sitter attractor indicates that torsion cosmology ...

For an unsteady baryonic gamma-ray burst (GRB) outflow, the fast and slow proton shells collide with each other and produce energetic soft gamma-ray emission. If the outflow has a significant neutron component, the ultrarelativistic neutrons initially expand freely until decaying at a larger radius....

We study an extension of the minimal supersymmetric standard model with a singlet supermultiplet S with coupling SH₁H₂ in order to solve the μ problem as in the next-to-minimal supersymmetric standard model, and right-handed neutrino supermultiplets N with couplings SNN in order to generate dynamic...

It is known that the total gravitational energy in localized sources that have static spherical symmetry and satisfy energy conditions is negative (attractive gravity). A natural query is how the gravitational energy behaves under circumstances where energy conditions are violated. To answer this, t...

We study the properties of the space of thermodynamic equilibrium states of the Bañados-Teitelboim-Zanelli (BTZ) black hole in (2+1) gravity. We use the formalism of geometrothermodynamics to introduce in the space of equilibrium states a two-dimensional thermodynamic metric whose curvature is nonv...

The dynamical breaking of gauge symmetry in the supersymmetric quantum electrodynamics in three-dimensional spacetime is studied at two-loop approximation. At this level, the effective superpotential is evaluated in a supersymmetric phase. At one-loop order, we observe a generation of the Chern-Simo...

Standard entropy calculations in quantum field theory, when applied to a subsystem of definite volume, exhibit area-dependent UV divergences that make a thermodynamic interpretation troublesome. In this paper we define a renormalized entropy which is related with the Newton-Wigner position operator....

We consider the decay of a metastable domain wall. The transition proceeds through quantum tunneling, and we calculate in an arbitrary number of dimensions the preexponential factor multiplying the leading semiclassical exponential expression for the rate of the process. We find that the effect of t...

Investigations of quantum Einstein gravity (QEG) based upon the effective average action employ a flow equation which does not contain any ultraviolet (UV) regulator. Its renormalization group trajectories emanating from a non-Gaussian fixed point define asymptotically safe quantum field theories. A...

Restricted Schur polynomials have been posited as orthonormal operators for the change of basis from N=4 SYM to type IIB string theory. In this paper we briefly expound the relationship between the restricted Schur polynomials and the operators forwarded by Brown, Heslop, and Ramgoolam. We then bri...

Control of systematic uncertainties in the use of type Ia supernovae as standardized distance indicators can be achieved through contrasting subsets of observationally characterized, like supernovae. Essentially, like supernovae at different redshifts reveal the cosmology, and differing supernovae ...

In this paper we study the Landau levels in the nonrelativistic dynamics of a neutral particle which possesses a permanent magnetic dipole moment interacting with an external electric field in the curved space-time background with the presence or absence of a torsion field. The eigenfunction and eig...

Although f(R) modified gravity models can be made to satisfy solar system and cosmological constraints, it has been shown that they have the serious drawback of the nonexistence of stars with strong gravitational fields. In this paper, we discuss whether or not higher curvature corrections can remed...

We construct a solution of two black holes on a Kaluza-Klein bubble in Einstein-Maxwell-dilaton theory. We explore the consequences of the presence of charge for the properties of this solution, and obtain a generalized Smarr relation and first law.

We explore the DL=2 same-sign dilepton signal from top-quark decay via a Majorana neutrino at the LHC in the top anti-top pair production samples. The signature is same-sign dilepton plus multi-jets with no significant missing energy. The most optimistic region lies where the Majorana neutrino mass is between 15-65 GeV. For 300 fb-1 integrated luminosity, it is possible to probe Sij, the effective mixing parameter, to O(10-5).

We analyze the phenomenology of a prolonged early epoch of matter domination by an unstable but very long-lived massive particle. This new matter domination era can help to relax some of the requirements on the primordial inflation. Its main effect is the huge entropy production produced by the decays of such particle that can dilute any possible unwanted relic, as the gravitino in supersymmetric models, and thus relax the constraints on the inflationary reheating temperature. A natural candidate for such heavy, long-lived particle already present in the Standard Model of the electroweak interactions would be a heavy right-handed neutrino. In this case, we show that its decays can also generate the observed baryon asymmetry with right-handed neutrino masses well above the bound from gravitino overproduction.

We present a detailed analysis of the Bc form factors in the BSW framework, by investigating the effects of the flavor dependence on the average transverse quark momentum inside a meson. Branching ratios of two body decays of Bc meson to pseudoscalar and vector mesons are predicted.

Within a theoretical framework that accounts for all open-charm mesons, including the D0*(2308), the DsJ*(2317) and the DsJ(2460), we analyze the structure and explore possible quantum number assignments for the DsJ(2860) and the DsJ(2700) mesons reported by BABAR and Belle Collaborations. The open-charm sector is properly described if considered as a combination of conventional quark-antiquark states and four-quark components. All negative parity and 2+ states can be understood in terms only of q[`q] components, however the description of the 0+ and 1+ mesons is improved whenever the mixing between two- and four-quarks configurations is included. We analyze all possible quantum number assignments for the DsJ(2860) in terms of both c[`s] and cn[`s][`n] configurations. We discuss the role played by the electromagnetic and strong decay widths as basic tools to distinguish among them. The broad structure reported by BABAR near 2.7 GeV is also analyzed. Keywords: Charm mesons, Charm-strange mesons, quark models. Pacs: 14.40.Lb, 14.40.Ev, 12.39.Pn.

systematically analyze the Dirac and the Majorana mass matrices in seesaw models with two heavy right-handed neutrinos. We perform thorough classification of the vanishing matrix elements which are compatible with the results from the current neutrino oscillation experiments. We include the possibility of a non-diagonal Majorana mass matrix which leads to new solutions viable with data. In a basis where the Majorana mass matrix is diagonal, these solutions imply a Dirac matrix with specific relationships amongst its elements. We find that at the level of total 4 zeros together in mD and MR the mass matrices are almost consistent with the data but one mixing angle is predicted to be unsuitable. At the next level, i.e. with total 3 zeros, only seven patterns of mass matrices describe the experimental data well. The seven solutions have testable predictions for the future neutrino experiments. In particular, each solution has definite predictions about the observation of the 1-3 leptonic mixing angle and the effective mass measured in neutrino-less double beta decay. The solutions of the mass matrices contain novel texture forms and provide new insights into the lepton-generation structure. We also discuss possible connections between these textures and the tri-bimaximal mixing to search for symmetry principles behind the mass matrix structure.

Extending the standard model with three right-handed neutrinos (Nk) and a second Higgs doublet (h), odd under the discrete parity symmetry Z2, Majorana neutrino masses can be generated at 1-loop order. In the resulting model, the lightest stable particle, either a boson or a fermion, might be a dark matter candidate. Here we assume a specific mass spectrum (M1 << M2 < M3 < mh) and derive its consequences for dark matter and collider phenomenology. We show that (i) the lightest right-handed neutrino is a warm dark matter particle that can give a ~ 10% contribution to the dark matter density; (ii) several decay branching ratios of the charged scalar can be predicted from measured neutrino data. Especially interesting is that large lepton flavour violating rates in muon and tau final states are expected. Finally, we derive upper bounds on the right-handed neutrino Yukawa couplings from the current experimental limit on Br(meg).

We study weak decays of the charm- and bottom-strange mesons Ds0*(2317), Ds1(2460), Bs0*(5725) and Bs1(5778) with f0(980) in the final state by assuming a hadronic molecule interpretation for their structures. Since in the proposed framework the initial and final states are occupied by hadronic molecules, the predictions for observables can provide a sensitive tool to further test the hadronic molecule structure in future experiments.

We obtain explicitly the renormalization group equations for the quark mass matrices in terms of a set of rephasing invariant parameters. For a range of assumed high energy values for the mass ratios and mixing parameters, they are found to evolve rapidly and develop hierarchies as the energy scale decreases. To achieve the experimentally observed high degree of hierarchy, however, the introduction of new models with specific properties becomes necessary.

We investigate the influence of the universal extra dimension on the branching ratio in the B \rar p(r) l+ l- decay. Taking 1/R ~ {200-1000}GeV with one universal extra spatial dimension, which is consistent with the experimental data for B(B Xsg) , B(B K* m+m- ) and the electroweak precision tests, we obtain that for both (m,  t) channels the branching ratio strongly depends on the compactification radius 1/R.

The question of whether neutrino masses are Dirac or Majorana is one of the most important, and most difficult, questions remaining in the neutrino sector. Searches for neutrinoless double b-decay may help to resolve this question, but are also sensitive to new, higher dimension DL=2 operators. In this paper we place two phenomenological constraints on these operators at dimension d 11. First, we require that the operators obey the quark flavor symmetries of the Standard Model, with any violation of the symmetries being due to Yukawa interactions, a scheme known as Minimal Flavor Violation (MFV). Second, we require that the operators which generate neutrinoless double b-decay, and any operators related by the flavor symmetries, do not induce neutrino masses above the experimental and astrophysical limits. We find that these requirements severely constrain the operators which can violate lepton number, such that most can no longer contribute to neutrinoless double b-decay at observable rates. It is noteworthy that quark flavor symmetries can play such a strong role in constraining new leptonic physics, even when that physics is not quark flavor changing. Those few operators that can mimic a Majorana neutrino mass then appear with cutoffs below a TeV, and represent new physics which could be directly probed at the LHC or a future linear collider.

We study two-photon exchange (TPE) in the elastic electron-nucleon scattering at high Q2 in the framework of pQCD. The obtained TPE amplitude is of order a/as with respect to Born approximation. Its shape and value are sensitive to the choice of nucleon wavefunction, thus study of TPE effects can provide important information about nucleon structure. With the wavefunctions based on QCD sum rules, TPE correction to the electron-proton cross section has negative sign, is almost linear in \ve and grows logarithmically with Q2 up to 7% at Q2 = 30\GeV2. The results of existing "hadronic" calculations, taking into account just the nucleon intermediate state, can be smoothly connected with the pQCD result near Q2 ~ 3\GeV2. Above this point two methods disagree, which implies that "hadronic" approach becomes inadequate at high Q2. Other relevant observables, such as electron/positron cross section ratio, are also discussed.

Torsion models constitute a well known class of extended quantum gravity models. In this paper we study some phenomenological consequences of a torsion field interacting with fermions at LHC. A torsion field could appear as a new heavy state characterized by its mass and couplings to fermions. These new states will form a resonance decaying into difermions, as occurs in many extensions of the Standard Model, such as models predicting the existence of additional neutral gauge bosons, usually named Z. Using the dielectron channel we evaluate the integrated luminosity needed for a 5s discovery as a function of the torsion mass, for different coupling values. We also calculate the luminosity needed for discriminate, with 95% C.L., the two possible different torsion natures. Finally, we show that the observed signal coming from the torsion field could be distinguished from a signal coming from a new neutral gauge boson, provided there is enough luminosity.

One of the simplest extensions of the Standard Model that explains the observed abundance of dark matter is the inert doublet model. In this theory a discrete symmetry ensures that the neutral component of an additional electroweak doublet scalar is stable, and constitutes a dark matter candidate. As massive bodies such as the Sun and Earth move through the dark matter halo, dark matter particles can become gravitationally trapped in their cores. Annihilations of these particles result in neutrinos, which can potentially be observed with neutrino telescopes. We calculate the neutrino detection rate at these experiments from inert doublet dark matter annihilations in the cores of the Sun and the Earth.

The forward limit of the chiral-odd generalized parton distributions (GPDs) and their lower moments are investigated within the framework of the chiral quark soliton model (CQSM), with particular emphasis upon the transversity decomposition of nucleon angular momentum proposed by Burkardt. A strong correlation between quark spin and orbital angular momentum inside the nucleon is manifest itself in the derived second moment sum rule within the CQSM, thereby providing with an additional support to the qualitative connection between chiral-odd GPDs and the Boer-Mulders effects. We further confirm isoscalar dominance of the corresponding first moment sum rule, which indicates that the Boer-Mulders functions for the u- and d-quarks have roughly equal magnitude with the same sign. Also made are some comments on the recent empirical extraction of the tensor charges of the nucleon by Anselmino et al. We demonstrate that a comparison of their result with any theoretical predictions must be done with great care, in consideration of fairly strong scale dependence of tensor charges, especially at lower renormalization scale.

We study the stability of AdS black hole holes rotating in a single two plane for tensor-type gravitational perturbations in D > 6 space-time dimensions. First, by an analytic method, we show that there exists no unstable mode when the magnitude a of the angular momentum is smaller than rh2/R where rh is the horizon radius, and R is the AdS curvature radius. Then, by numerical calculations of quasinormal modes, using the separability of the relevant perturbation equations, we show that an instability occurs for rapidly rotating black holes with a > rh2/R, although the growth rate is tiny (of order 10-12 of the inverse horizon radius). We give numerical evidences indicating that this instability is caused by superradiance.

In this paper we derive the probability of the radial profiles of spherically symmetric inhomogeneities in order to provide an improved estimation of the number density of primordial black holes (PBHs). We demonstrate that the probability of PBH formation depends sensitively on the radial profile of the initial configuration. We do this by characterising this profile with two parameters chosen heuristically: the amplitude of the inhomogeneity and the second radial derivative, both evaluated at the centre of the configuration. We calculate the joint probability of initial cosmological inhomogeneities as a function of these two parameters and then find a correspondence between these parameters and those used in numerical computations of PBH formation. Finally, we extend our heuristic study to evaluate the probability of PBH formation taking into account for the first time the radial profile of curvature inhomogeneities.

We explore the consequences of the existence of a very large number of light scalar degrees of freedom in the early universe. We distinguish between participator and spectator fields. The former have a small mass, and can contribute to the inflationary dynamics; the latter are either strictly massless or have a negligible VEV. In N-flation and generic assisted inflation scenarios, inflation is a co-operative phenomenon driven by N participator fields, none of which could drive inflation on its own. We review upper bounds on N, as a function of the inflationary Hubble scale H. We then consider stochastic and eternal inflation in models with N participator fields showing that individual fields may evolve stochastically while the whole ensemble behaves deterministically, and that a wide range of eternal inflationary scenarios are possible in this regime. We then compute one-loop quantum corrections to the inflationary power spectrum. These are largest with N spectator fields and a single participator field, and the resulting bound on N is always weaker than those obtained in other ways. We find that loop corrections to the N-flation power spectrum do not scale with N, and thus place no upper bound on the number of participator fields. This result also implies that, at least to leading order, the theory behaves like a composite single scalar field. In order to perform this calculation, we address a number of issues associated with loop calculations in the Schwinger-Keldysh "in-in" formalism.

Katz and Vafa showed how charged matter can arise geometrically by the deformation of ADE-type orbifold singularities in type IIa, M-theory, and F-theory compactifications. In this paper we use those same basic ingredients, used there to geometrically engineer specific matter representations, here to deform the compactification manifold itself in a way which naturally compliments many features of unified model building. We realize this idea explicitly by deforming a manifold engineered to give rise to an SU5 grand unified model into a one giving rise to the Standard Model. In this framework, the relative local positions of the singularities giving rise to Standard Model fields are specified in terms of the values of a small number of complex structure moduli which deform the original manifold, greatly reducing the arbitrariness of their relative positions.

In a holographic black hole solution is discussed which exhibits a superconductor like transition. In the superconducting phase the black holes show infinite DC conductivity. This gives rise to the possibility of deforming the solutions by turning on a time independent current (supercurrent), without any electric field. This type of deformation does not exist for normal (non-superconducting) black holes, due to the no-hair theorems. In this paper we have studied such a supercurrent solution and the associated phase diagram. Interestingly, we have found a "special point" (critical point) in the phase diagram where the second order superconducting phase transition becomes first order. Supercurrent in superconducting materials is a well studied phenomenon in condensed matter systems. We have found some qualitative agreement with known results.

\\[5mm]\parbox{13cm}{\footnotesize \noi In this paper we investigate in detail the correspondence between $E_{10}$ and Romans' massive deformation of type IIA supergravity. We analyse the dynamics of a non-linear sigma model for a spinning particle on the coset space $E_{10}/K(E_{10})$ and show that it reproduces the dynamics of the bosonic as well as the fermionic sector of the massive IIA theory, within the standard truncation. The mass deformation parameter corresponds to a generator of $E_{10}$ outside the realm of the generators entering the usual $D=11$ analysis, and is naturally included without any deformation of the coset model for $E_{10}/K(E_{10})$. Our analysis thus provides a dynamical unification of the massless and massive versions of type IIA supergravity inside $E_{10}$. We discuss a number of additional and general features of relevance in the analysis of any deformed supergravity in the correspondence to Kac-Moody algebras, including recently studied deformations where the trombone symmetry is gauged. } \noindent

Viable models of modified gravity which satisfy both local as well as cosmological tests are investigated. It is demonstrated that some versions of such highly non-linear models exhibit multiply de Sitter universe solutions, which often appear in pairs, being one of them stable and the other unstable. It is explicitly shown that, for some values of the parameters, it is possible to find several de Sitter spaces (as a rule, numerically); one of them may serve for the inflationary stage, while the other can be used for the description of the dark energy epoch. The numerical evolution of the effective equation of state parameter is also presented, showing that these models can be considered as natural candidates for the unification of early-time inflation with late-time acceleration through dS critical points. Moreover, based on the de Sitter solutions, multiply SdS universes are constructed which might also appear at the (pre-)inflationary stage. Their thermodynamics are studied and free energies are compared.

An explicit and simple solution representing the wormhole formation is presented. The spacetime is constructed by gluing the Minkowski and Roberts spacetimes at null hypersurfaces in a regular manner. The parameters in the Roberts solution are required to give the negative kinetic term for the massless scalar field. Although a curvature singularity appears at the moment of the wormhole formation, it disappears instantaneously. This instantaneous singularity is weak in the both senses of Tipler and Królak along radial causal geodesics.

We investigate spherically symmetric non topological solitons in electrodynamics with a scalar field self interaction U ~ |y| taken from the complex signum-Gordon model. We find Q-balls for small absolute values of the total electric charge Q, and Q-shells when |Q| is large enough. In both cases the charge density exactly vanishes outside certain compact region in the three dimensional space. The dependence of the total energy E of small Q-balls on the total electric charge has the form E ~ |Q|5/6, while in the case of very large Q-shells E ~ |Q|7/6.

The properties of the Gribov region in SU(2) Euclidean Yang-Mills theories in the maximal Abelian gauge are investigated. This region turns out to be bounded in all off-diagonal directions, while it is unbounded along the diagonal one. The soft breaking of the BRST invariance due to the restriction of the domain of integration in the path integral to the Gribov region is scrutinized. Owing to the unboundedness in the diagonal direction, the invariance with respect to Abelian transformations is preserved, a property which is at the origin of the local U(1) Ward identity of the maximal Abelian gauge.

The familiar Fock space commonly used to describe the relativistic harmonic oscillator, for example as part of string theory, is insufficient to describe all the states of the relativistic oscillator. We find that there are three different vacua leading to three disconnected Fock sectors, all constructed with the same creation-annihilation operators. These have different spacetime geometric properties as well as different algebraic symmetry properties or different quantum numbers. Two of these Fock spaces include negative norm ghosts (as in string theory) while the third one is completely free of ghosts. We discuss a gauge symmetry in a worldline theory approach that supplies appropriate constraints to remove all the ghosts from all Fock sectors of the single oscillator. The resulting ghost free quantum spectrum in d+1 dimensions is then classified in unitary representations of the Lorentz group SO(d,1). Moreover all states of the single oscillator put together make up a single infinite dimensional unitary representation of a hidden global symmetry SU(d,1), whose Casimir eigenvalues are computed. Possible applications of these new results in string theory and other areas of physics and mathematics are briefly mentioned.