arXiv.org: High-Energy Physics: Theory

hep-th updates on arXiv.org

• Orbifold equivalence and the sign problem at finite baryon density. (arXiv:1009.1623v1 [hep-th])
  

  We point out that SO(2N_{c}) gauge theory with N_{f} fundamental Dirac fermions does not have a sign problem at finite baryon number chemical potential \mu_{B}. One can thus use lattice Monte Carlo simulations to study this theory at finite density. The absence of a sign problem in the SO(2N_{c}) theory is particularly interesting because a wide class of observables in the SO(2N_{c}) theory coincide with observables in QCD in the large N_{c} limit, as we show using the technique of large N_{c} orbifold equivalence. We argue that the orbifold equivalence between the two theories continues to hold at \mu_{B} \neq 0 provided one adds appropriate deformation terms to the SO(2N_{c}) theory. This opens up the prospect of learning about QCD at \mu_{B} \neq 0 using lattice studies of the SO(2N_{c}) theory.

  
  
  
• Minimal Supersymmetric Conformal Technicolor: The Perturbative Regime. (arXiv:1009.1624v1 [hep-ph])
  

  We investigate the perturbative regime of the Minimal Supersymmetric Conformal Technicolor and show that it allows for a stable vacuum correctly breaking the electroweak symmetry. We find that the particle spectrum is richer than the MSSM one since it features several new particles stemming out from the new N = 4 sector of the theory. The parameter space of the new theory is reduced imposing naturality of the couplings and soft supersymmetry breaking masses, perturbativity of the model at the EW scale as well as phenomenological constraints. Our preliminary results on the spectrum of the theory suggest that the Tevatron and the LHC can rule out a significant portion of the parameter space of this model.

  
  
  
• E7(7) constraints on counterterms in N=8 supergravity. (arXiv:1009.1643v1 [hep-th])
  

  We prove by explicit computation that the operators D^4R^4 and D^6R^4 in N=8 supergravity have non-vanishing single-soft scalar limits at the 6-point level, and therefore they violate the continuous E7(7) symmetry. The soft limits precisely match automorphism constraints. Together with previous results for R^4, this provides a direct proof that no E7(7)-invariant candidate counterterm exists below 7-loop order. At 7-loops, we characterize the infinite tower of independent supersymmetric operators D^4R^6, R^8, phi^2 R^8,... with n>4 fields and prove that they all violate E7(7) symmetry. This means that the 4-graviton amplitude determines finiteness at 7-loop order. We show that the corresponding candidate counterterm D^8R^4 has a non-linear supersymmetrization such that its single- and double-soft scalar limits are compatible with E7(7) up to and including 6-points. At loop orders 7, 8, 9 we provide an exhaustive account of all independent candidate counterterms with up to 16, 14, 12 fields, respectively, together with their potential single-soft scalar limits.

  
  
  
• A Near Horizon CFT Dual for Kerr-Newman-$AdS$. (arXiv:1009.1661v1 [hep-th])
  

  We consider quantum gravitational effects in the near horizon regime of a Kerr-Newman-$AdS$ (KN$AdS$) black hole. In this regime we construct a holographic two-dimensional CFT in the form of a Liouville/Polyakov action. The Liouville/Polyakov theory is solved via a two dimensional metric a la Robinson and Wilczek and by employing Unruh Vacuum boundary conditions. The resulting CFT's energy-momentum-tensor is anomalous, yet in the horizon limit is dominated by one holomorphic component containing the Hawking Temperature of the KN$AdS$ black hole. Furthermore, we compute the CFT's Virasoro algebra on the horizon, whose central charge reproduces the correct Bekenstein-Hawking Entropy via Cardy's Formula. Our derived central charge also agrees with the near extremal Kerr/CFT Correspondence in the appropriate limits. This provides a uniform framework for computing both entropy and temperature by combining the holographic principle with the effective action approach.

  
  
  
• Localization of gravity on a thick braneworld without scalar fields. (arXiv:1009.1684v1 [hep-th])
  

  In this work we present a simple thick braneworld model that is generated by an intriguing interplay between a 5D cosmological constant with a de Sitter metric induced in the 3-brane without the inclusion of scalar fields. We show that 4D gravity is localized on this brane, provide analytic expressions for the massive Kaluza-Klein (KK) fluctuation modes and also show that the spectrum of metric excitations displays a mass gap. We finally present the corrections to Newton's law due to these massive modes. This model has no naked singularities along the fifth dimension despite the existence of a mass gap in the graviton spectrum as it happens in thick branes with 4D Poincare symmetry, providing a simple model with very good features: the curvature is completely smooth along the fifth dimension, it localizes 4D gravity and the spectrum of gravity fluctuations presents a mass gap, a fact that rules out the existence of phenomenologically dangerous ultralight KK excitations in the model.

  
  
  
• Effects of Matrix Orientifolding to Two-Loop Effective Action of Bosonic IIB Matrix Model. (arXiv:1009.1695v1 [hep-th])
  

  We study the spacetime structures which are described by the IIB matrix model with orientifolding. Matrix orientifolding that preserves supersymmetries yields the mirror image point with respect to a four-dimensional plane for each spacetime point that corresponds to the eigenvalue of the bosonic matrix. In order to consider the upper bound on the distance between two eigenvalues in this model, we calculate the effective action for the eigenvalues up to two-loop. The eigenvalues distribute in a tubular region around the four-dimensional plane.

  
  
  
• Ho\u{r}ava-Lifshitz Gravity on Primordial Black Holes. (arXiv:1009.1703v1 [hep-th])
  

  We tested the Ho\u{r}ava Lifshitz (HL) quantum gravity model by using the L{\" u}, Mei and Pope solutions for primordial black holes (PBHs) and the observational upper bounds of the PBH density parameters. We found that, although the HL model is severely constrained, it is not ruled out. When our analysis is combined with that of Dutta and Saridakis the observed value of the density parameter $\Omega_{PBH}$ might rise by several percent as the running energy parameter $\lambda$ increases.

  
  
  
• The sparticle spectrum in Minimal gaugino-Gauge Mediation. (arXiv:1009.1714v1 [hep-ph])
  

  We compute the sparticle mass spectrum in the minimal four-dimensional construction that interpolates between gaugino mediation and ordinary gauge mediation.

  
  
  
• Improved ground-state estimate by thermal resummation. (arXiv:1009.1715v1 [hep-th])
  

  For the deconfining phase of SU(2) Yang-Mills thermodynamics and for high temperatures we point out that a linear dependence on temperature of a one-loop selfconsistently resummed thermal correction to the pressure and the energy density takes place despite a quartic dependence arising from an unsummed two-loop correction. This linearity is hierarchically smaller than the one belonging to the tree-level estimate of the thermal ground-state. We discuss and interprete this result.

  
  
  
• Asymptotic Safety in Einstein Gravity and Scalar-Fermion Matter. (arXiv:1009.1735v1 [hep-th])
  

  Within the functional renormalization group approach we study the effective QFT of Einstein gravity and one self-interacting scalar coupled to N_f Dirac fermions. We include in our analysis the matter anomalous dimensions induced by all the interactions and analyze the highly non linear beta functions determining the renormalization flow. We find the existence of a non trivial fixed point structure both for the gravity and the matter sector, besides the usual gaussian matter one. This suggest that asymptotic safety could be realized in the gravitational sector \emph{and} in the standard model. Non triviality in the Higgs sector might involve gravitational interactions.

  
  
  
• Awaking the vacuum in relativistic stars. (arXiv:1009.1771v1 [gr-qc])
  

  Void of any inherent structure in classical physics, the vacuum has revealed to be incredibly crowded with all sorts of processes in relativistic quantum physics. Yet, its direct effects are usually so subtle that its structure remains almost as evasive as in classical physics. Here, in contrast, we report on the discovery of a novel effect according to which the vacuum is compelled to play an unexpected central role in an astrophysical context. We show that the formation of relativistic stars may lead the vacuum energy density of a quantum field to an exponential growth. The vacuum-driven evolution which would then follow may lead to unexpected implications for astrophysics, while the observation of stable neutron-star configurations may teach us much on the field content of our Universe.

  
  
  
• The Betti numbers of the moduli space of stable sheaves of rank 3 on P2. (arXiv:1009.1775v1 [math-ph])
  

  This article computes the generating functions of the Betti numbers of the moduli space of stable sheaves of rank 3 on the projective plane P2 and its blow-up. Wall-crossing is used to obtain the Betti numbers on the blow-up. These can be derived equivalently using flow trees, which appear in the physics of BPS-states. The Betti numbers for P2 follow from those for the blow-up by the blow-up formula. The generating functions are expressed in terms of modular functions and indefinite theta functions.

  
  
  
• Quantum Fluctuations of Vector Fields and the Primordial Curvature Perturbation in the Universe. (arXiv:1009.1779v1 [astro-ph.CO])
  

  The \delta N formalism is extended to include the perturbation of the vector field. The latter is quantized in de Sitter space-time and it is found that in general the particle production process of the vector field is anisotropic. This anisotropy is parametrized by introducing two parameters p and q, which are determined by the conformal invariance breaking mechanism. If any of them are non-zero, generated \zeta is statistically anisotropic. Then the power spectrum of \zeta and the non-linearity parameter fNL have an angular modulation. This formalism is applied for two vector curvaton models and the end-of-inflation scenario. It is found that for p \ne 0, the magnitude of fNL and the direction of its angular modulation is correlated with the anisotropy in the spectrum. If p \gtrsim 1, the anisotropic part of fNL is dominant over the isotropic one. These are distinct observational signatures; their detection would be a smoking gun for a vector field contribution to \zeta . In the first curvaton model the vector field is non-minimally coupled to gravity and in the second one it has a time varying kinetic function and mass. In the former, only statistically anisotropic \zeta can be generated, while in the latter, isotropic \zeta may be realized too. Parameter spaces for these vector curvaton scenarios are large enough for them to be realized in the particle physics models. In the end-of-inflation scenario fNL have similar properties to the vector curvaton scenario with additional anisotropic term.

  
  
  
• A Note on Charged Black Holes in AdS space and the Dual Gauge Theories. (arXiv:1009.1780v1 [hep-th])
  

  We study the thermodynamics and the phase structures of Reissner-Nordstrom and Born-Infeld black holes in AdS space by constructing ``off-shell'' free energies using thermodynamic quantities derived directly from the action. We then use these results to propose ``off-shell'' effective potentials for the respective boundary gauge theories. The saddle points of the potentials describe all the equilibrium phases of the gauge theories.

  
  
  
• On thermodynamics second law in Gauss Bonnet gravity. (arXiv:1009.1839v1 [gr-qc])
  

  Validity of the second and the generalized second law of thermodynamics in cosmology in the frame work of Gauss-Bonnet theory of gravity is investigated. The necessary conditions upon which these laws hold are derived and discussed.

  
  
  
• MHV Diagrams in Momentum Twistor Space. (arXiv:1009.1854v1 [hep-th])
  

  We show that there are remarkable simplifications when the MHV diagram formalism for N=4 super Yang-Mills is reformulated in momentum twistor space. The vertices are replaced by unity while each propagator becomes a dual superconformal `R-invariant' whose arguments may be read off from the diagram. The momentum twistor MHV rules generate a formula for the full, all-loop planar integrand of the super Yang-Mills S-matrix that is manifestly dual superconformally invariant up to the choice of a reference twistor. We give a general proof of this reformulation and illustrate its use by computing the momentum twistor NMHV and NNMHV tree amplitudes and the integrands of the MHV and NMHV 1-loop and the MHV 2-loop planar amplitudes.

  
  
  
• Exotic Universal Solutions in Cubic Superstring Field Theory. (arXiv:1009.1865v1 [hep-th])
  

  We present a class of analytic solutions of cubic superstring field theory in the universal sector on a non-BPS D-brane. Computation of the action and gauge invariant overlap reveal that the solutions carry half the tension of a non-BPS D-brane. However, the solutions do not satisfy the reality condition. In fact, they display an intriguing topological structure: We find evidence that conjugation of the solutions is equivalent to a gauge transformation that cannot be continuously deformed to the identity.

  
  
  
• Inflationary Cosmology as a Probe of Primordial Quantum Mechanics. (arXiv:0805.0163v2 [hep-th] UPDATED)
  

  We show that inflationary cosmology may be used to test the statistical predictions of quantum theory at very short distances and at very early times. Hidden-variables theories, such as the pilot-wave theory of de Broglie and Bohm, allow the existence of vacuum states with non-standard field fluctuations ('quantum nonequilibrium'). We show that inflationary expansion can transfer microscopic nonequilibrium to macroscopic scales, resulting in anomalous power spectra for the cosmic microwave background. The conclusions depend only weakly on the details of the de Broglie-Bohm dynamics. We discuss, in particular, the nonequilibrium breaking of scale invariance for the primordial (scalar) power spectrum. We also show how nonequilibrium can generate primordial perturbations with non-random phases and inter-mode correlations (primordial non-Gaussianity). We address the possibility of a low-power anomaly at large angular scales, and show how it might arise from a nonequilibrium suppression of quantum noise. Recent observations are used to set an approximate bound on violations of quantum theory in the early universe.

  
  
  
• Dark Matter Production at LHC from Black Hole Remnants. (arXiv:0901.3358v3 [hep-ph] UPDATED)
  

  We study dark matter production at CERN LHC from black hole remnants (BHR). We find that the typical mass of these BHR at LHC is ~ 5-10 TeV which is heavier than other dark matter candidates such as: axion, axino, neutralino etc. We propose the detection of this dark matter via single jet production in the process pp -> jet +BHR(dark matter) at CERN LHC. We find that for zero impact parameter partonic collisions, the monojet cross section is not negligible in comparison to the standard model background and is much higher than the other dark matter scenarios studied so far. We also find that d\sigma/dp_T of jet production in this process increases as p_T increases, whereas in all other dark matter scenarios the d\sigma/dp_T decreases at CERN LHC. This may provide an useful signature for dark matter detection at LHC. However, we find that when the impact parameter dependent effect of inelasticity is included, the monojet cross section from the above process becomes much smaller than the standard model background and may not be detectable at LHC.

  
  
  
• The Einstein-Maxwell-Particle System in the York Canonical Basis of ADM Tetrad Gravity: I) The Equations of Motion in Arbitrary Schwinger Time Gauges. (arXiv:0907.4087v3 [gr-qc] UPDATED)
  

  We study the coupling of N charged scalar particles plus the electro-magnetic field to ADM tetrad gravity and its canonical formulation in asymptotically Minkowskian space-times without super-translations. We make the canonical transformation to the York canonical basis, where there is a separation between the {\it inertial} (gauge) variables and the {\it tidal} ones inside the gravitational field and a special role of the Eulerian observers associated to the 3+1 splitting of space-time. The Dirac Hamiltonian is weakly equal to the weak ADM energy. The Hamilton equations in Schwinger time gauges are given explicitly. In the York basis they are naturally divided in four sets: a) the contracted Bianchi identities; b) the equations for the inertial gauge variables; c) the equations for the tidal ones; d) the equations for matter. Finally we give the restriction of the Hamilton equations and of the constraints to the family of {\it non-harmonic 3-orthogonal} gauges, in which the instantaneous Riemannian 3-spaces have a diagonal 3-metric. The non-fixed inertial gauge variable ${}^3K$ (the freedom in the clock synchronization convention) gives rise to a negative kinetic term in the weak ADM energy vanishing only in the gauges with ${}^3K = 0$: is it relevant for dark energy and back-reaction? In the second paper there will be the linearization of the theory to obtain Hamiltonian post-Minkowskian gravity with asymptotic Minkowski background, non-flat instantaneous 3-spaces and no post-Newtonian expansion. This will allow to explore the inertial effects induced by the York time ${}^3K$ in non-flat 3-spaces and to check how much dark matter can be explained as an inertial aspect of Einstein's general relativity.

  
  
  
• Electroweak stars: how nature may capitalize on the standard model's ultimate fuel. (arXiv:0912.0520v2 [hep-ph] UPDATED)
  

  We study the possible existence of an electroweak star - a compact stellar-mass object whose central core temperature is higher than the electroweak symmetry restoration temperature. We found a solution to the Tolman-Oppenheimer-Volkoff equations describing such an object. The parameters of such a star are not substantially different from a neutron star - its mass is around 1.3 Solar masses while its radius is around 8 km. What is different is the existence of a small electroweak core. The source of energy in the core that can at least temporarily balance gravity are standard-model non-perturbative baryon number (B) and lepton number (L) violating processes that allow the chemical potential of $B+L$ to relax to zero. The energy released at the core is enormous, but gravitational redshift and the enhanced neutrino interaction cross section at these energies make the energy release rate moderate at the surface of the star. The lifetime of this new quasi-equilibrium can be more than ten million years. This is long enough to represent a new stage in the evolution of a star if stellar evolution can take it there.

  
  
  
• Bosons, fermions and anyons in the plane, and supersymmetry. (arXiv:1001.0274v4 [hep-th] UPDATED)
  

  Universal vector wave equations allowing for a unified description of anyons, and also of usual bosons and fermions in the plane are proposed. The existence of two essentially different types of anyons, based on unitary and also on non-unitary infinite-dimensional half-bounded representations of the (2+1)D Lorentz algebra is revealed. Those associated with non-unitary representations interpolate between bosons and fermions. The extended formulation of the theory includes the previously known Jackiw-Nair (JN) and Majorana-Dirac (MD) descriptions of anyons as particular cases, and allows us to compose bosons and fermions from entangled anyons. The theory admits a simple supersymmetric generalization, in which the JN and MD systems are unified in N=1 and N=2 supermultiplets. Two different non-relativistic limits of the theory are investigated. The usual one generalizes Levy-Leblond's spin 1/2 theory to arbitrary spin, as well as to anyons. The second, "Jackiw-Nair" limit (that corresponds to Inonu-Wigner contraction with both anyon spin and light velocity going to infinity), is generalized to boson/fermion fields and interpolating anyons. The resulting exotic Galilei symmetry is studied in both the non-supersymmetric and the supersymmetric cases.

  
  
  
• Chaotic Maps, Hamiltonian Flows, and Holographic Methods. (arXiv:1002.0104v4 [nlin.CD] UPDATED)
  

  Holographic functional methods are introduced as probes of discrete time-stepped maps that lead to chaotic behavior. The methods provide continuous time interpolation between the time steps, thereby revealing the maps to be quasi-Hamiltonian systems underlain by novel potentials that govern the motion of a perceived point particle. Between turning points, the particle is strictly driven by Hamiltonian dynamics, but at each encounter with a turning point the potential changes abruptly, loosely analogous to the switchbacks on a mountain road. A sequence of successively deepening switchback potentials explains, in physical terms, the frequency cascade and trajectory folding that occur on the particular route to chaos revealed by the logistic map.

  
  
  
• Stochastic growth of quantum fluctuations during slow-roll inflation. (arXiv:1003.1327v3 [hep-th] UPDATED)
  

  We compute the growth of the mean square of quantum fluctuations of test fields with small effective mass during a slowly changing, nearly de Sitter stage which took place in different inflationary models. We consider a minimally coupled scalar with a small mass, a modulus with an effective mass $ \propto H^2$ (with $H$ as the Hubble parameter) and a massless non-minimally coupled scalar in the test field approximation and compare the growth of their relative mean square with the one of gauge-invariant inflaton fluctuations. We find that in most of the single field inflationary models the mean square gauge invariant inflaton fluctuation grows {\em faster} than any test field with a non-negative effective mass. Hybrid inflationary models can be an exception: the mean square of a test field can dominate over the gauge invariant inflaton fluctuation one on suitably choosing parameters. We also compute the stochastic growth of quantum fluctuation of a second field, relaxing the assumption of its zero homogeneous value, in a generic inflationary model; as a main result, we obtain that the equation of motion of a gauge invariant variable associated, order by order, with a generic quantum scalar fluctuation during inflation can be obtained only if we use the number of e-folds as the time variable in the corresponding Langevin and Fokker-Planck equations for the stochastic approach. We employ this approach to derive some bounds in the case of a model with two massive fields.

  
  
  
• The Einstein-Maxwell-Particle System: II) The Weak Field Approximation in the Non-Harmonic 3-Orthogonal Gauges and Hamiltonian Post-Minkowskian Gravity: the N-Body Problem and Gravitational Waves with Asymptotic Background. (arXiv:1003.5143v2 [gr-qc] UPDATED)
  

  In this second paper we define a Post-Minkowskian (PM) weak field approximation leading to a linearization of the Hamilton equations of ADM tetrad gravity in the York canonical basis in a family of non-harmonic 3-orthogonal Schwinger time gauges. The York time ${}^3K$ (the relativistic inertial gauge variable, not existing in Newtonian gravity, parametrizing the family and connected to the freedom in clock synchronization, i.e. to the definition of the instantaneous 3-spaces) is put equal to an arbitrary numerical function. A ultraviolet cutoff on the matter allows a consistent linearization, which is shown to be the lowest order of a Hamiltonian Post-Minkowskian (HPM) expansion. We solve the constraints and the Hamilton equations for the tidal variables and we find Post-Minkowskian gravitational waves with asymptotic background (and the correct quadrupole emission formula and energy balance) propagating on dynamically determined non-Euclidean 3-spaces in these non-harmonic gauges. In conclusion we get a PM solution for the gravitational field and we identify a class of PM Einstein space-times, which will be studied in more detail in a third paper together with the PM equations of motion for the particles and their Post-Newtonian expansion (but in absence of the electro-magnetic field). Finally we make a discussion on the {\it gauge problem in general relativity} to understand which type of experimental observations may lead to a preferred choice for the inertial gauge variable ${}^3K$ in the PM space-times. In the third paper we will show that this choice is connected with the problem of dark matter.

  
  
  
• Cosmological models with Lagrange Multiplier Field. (arXiv:1003.6056v4 [astro-ph.CO] UPDATED)
  

  We first consider the Einstein-aether theory with a \emph{gravitational coupling} and a Lagrange multiplier field, and then consider the non-minimally coupled quintessence field theory with Lagrange multiplier field. We study the influence of the Lagrange multiplier field on these models. We show that the energy density evolution of the Einstein-aether field and the quintessence field are significantly modified. The energy density of the Einstein-aether is nearly a constant during the entire history of the Universe. The energy density of the quintessence field can also be kept nearly constant in the matter dominated Universe, or even exhibit a phantom-like behavior for some models. This suggests a possible dynamical origin of the cosmological constant or dark energy. Further more, for the canonical quintessence in the absence of gravitational coupling, we find that the quintessence scalar field can play the role of cold dark matter with the introduction of a Lagrange multiplier field. We conclude that the Lagrange multiplier field could play a very interesting and important role in the construction of cosmological models.

  
  
  
• Brane-World Gravity. (arXiv:1004.3962v2 [hep-th] UPDATED)
  

  The observable universe could be a 1+3-surface (the "brane") embedded in a 1+3+\textit{d}-dimensional spacetime (the "bulk"), with Standard Model particles and fields trapped on the brane while gravity is free to access the bulk. At least one of the \textit{d} extra spatial dimensions could be very large relative to the Planck scale, which lowers the fundamental gravity scale, possibly even down to the electroweak ($\sim$ TeV) level. This revolutionary picture arises in the framework of recent developments in M theory. The 1+10-dimensional M theory encompasses the known 1+9-dimensional superstring theories, and is widely considered to be a promising potential route to quantum gravity. At low energies, gravity is localized at the brane and general relativity is recovered, but at high energies gravity "leaks" into the bulk, behaving in a truly higher-dimensional way. This introduces significant changes to gravitational dynamics and perturbations, with interesting and potentially testable implications for high-energy astrophysics, black holes, and cosmology. Brane-world models offer a phenomenological way to test some of the novel predictions and corrections to general relativity that are implied by M theory. This review analyzes the geometry, dynamics and perturbations of simple brane-world models for cosmology and astrophysics, mainly focusing on warped 5-dimensional brane-worlds based on the Randall--Sundrum models. We also cover the simplest brane-world models in which 4-dimensional gravity on the brane is modified at \emph{low} energies -- the 5-dimensional Dvali--Gabadadze--Porrati models. Then we discuss co-dimension two branes in 6-dimensional models.

  
  
  
• Mesons as Open Strings in a Holographic Dual of QCD. (arXiv:1005.0655v3 [hep-th] UPDATED)
  

  We study meson spectrum obtained from massive open string modes in a holographic dual of QCD constructed on the basis of a D4/D8-brane configuration in type IIA string theory. The spectrum includes mesons with spin higher than one. Taking into account the effect of curved background perturbatively, we obtain a mass formula for these mesons, which exhibits the linear Regge behavior at the leading order with subleading non-linear corrections. We argue that the string spectrum captures some features of the observed meson spectrum. For example, a_2(1320), b_1(1235), \pi(1300), a_0(1450), etc., are identified as the first excited massive open string states and \rho_3(1690), \pi_2(1670), etc., are identified as the second excited states.

  
  
  
• Cosmological evolution in exponential gravity. (arXiv:1005.4574v3 [astro-ph.CO] UPDATED)
  

  We explore the cosmological evolution in the exponential gravity $f(R)=R +c_1 (1-e^{- c_2 R})$ ($c_{1, 2} = \mathrm{constant}$). We summarize various viability conditions and explicitly demonstrate that the late-time cosmic acceleration following the matter-dominated stage can be realized. We also study the equation of state for dark energy and confirm that the crossing of the phantom divide from the phantom phase to the non-phantom (quintessence) one can occur. Furthermore, we illustrate that the cosmological horizon entropy globally increases with time.

  
  
  
• Trispectrum estimator in equilateral type non-Gaussian models. (arXiv:1007.1462v2 [hep-th] UPDATED)
  

  We investigate an estimator to measure the primordial trispectrum in equilateral type non-Gaussian models such as k-inflation, single field DBI inflation and multi-field DBI inflation models from Cosmic Microwave Background (CMB) anisotropies. The shape of the trispectrum whose amplitude is not constrained by the bispectrum in the context of effective theory of inflation and k-inflation is known to admit a separable form of the estimator for CMB anisotropies. We show that this shape is $87 \%$ correlated with the full quantum trispectrum in single field DBI inflation, while it is $33 \%$ correlated with the one in multi-field DBI inflation when curvature perturbation is originated from purely entropic contribution. This suggests that $g_{\rm NL} ^{equil}$, the amplitude of this particular shape, provides a reasonable measure of the non-Gaussianity from the trispectrum in equilateral non-Gaussian models. We relate model parameters such as the sound speed, $c_s$ and the transfer coefficient from entropy perturbations to the curvature perturbation, $T_{\mathcal{R} S}$ with $g_{\rm NL} ^{equil}$, which enables us to constrain model parameters in these models once $g_{\rm NL}^{equil}$ is measured in WMAP and Planck.

  
  
  
• String-Gauge Dual Description of Deep Inelastic Scattering at Small-$x$. (arXiv:1007.2259v2 [hep-ph] UPDATED)
  

  The AdS/CFT correspondence in principle gives a new approach to deep inelastic scattering as formulated by Polchinski and Strassler. Subsequently Brower, Polchinski, Strassler and Tan (BPST) computed the strong coupling kernel for the vacuum (or Pomeron) contribution to total cross sections. By identifying deep inelastic scattering with virtual photon total cross section, this allows a self consistent description at small-$x$ where the dominant contribution is the vacuum exchange process. Here we formulate this contribution and compare it with HERA small-$x$ DIS scattering data. We find that the BPST kernel along with a very simple local approximation to the proton and current "wave functions" gives a remarkably good fit not only at large $Q^2$ dominated by conformal symmetry but also extends to small $Q^2$, supplemented by a hard-wall cut-off of the AdS in the IR. We suggest that this is a useful phenomenological parametrization with implications for other diffractive processes, such as double diffractive Higgs production.

  
  
  
• Arbitrary p-form Galileons. (arXiv:1007.5278v2 [gr-qc] UPDATED)
  

  We show that scalar, 0-form, Galileon actions --models whose field equations contain only second derivatives-- can be generalized to arbitrary even p-forms. More generally, they need not even depend on a single form, but may involve mixed p combinations, including equal p multiplets, where odd p-fields are also permitted: We construct, for given dimension D, general actions depending on scalars, vectors and higher p-form field strengths, whose field equations are of exactly second derivative order. We also discuss and illustrate their curved-space generalizations, especially the delicate non-minimal couplings required to maintain this order. Concrete examples of pure and mixed actions, field equations and their curved space extensions are presented.

  
  
  
• Fierz-Pauli equation for massive gravitons from Induced Matter theory of gravity. (arXiv:1008.1958v2 [gr-qc] UPDATED)
  

  Starting with a 5D physical vacuum described by a 5D Ricci-flat background metric, we study the emergence of gravitational waves (GW) from the Induce Matter (IM) theory of gravity. We obtain the equation of motion for GW on an 4D curved spacetime which has the form of a Fierz-Pauli one. In our model the mass of gravitons $m_g$ is induced by a static foliation on the noncompact space-like extra dimension and the source-term is originated in the interaction of the GW with the induced connections of the background 5D metric. Here, relies the main difference of this formalism with the original Fierz-Pauli one.

  
  
  
• Precise constants in bosonization formulas on Riemann surfaces II. (arXiv:1008.2914v2 [math.DG] UPDATED)
  

  We give explicit formulas for the constants appearing in bosonization formulas on Riemann surfaces relating zeta regularized determinants of Laplace type operators associated to holomorphic line bundles of varying degree. We find that the constants $B_{g,d}$, which depend on the genus $g$ of the surface and the degree $d$ of the line bundle, satisfy the relation $B_{g,d}=(2\pi)^{2g-2-d} B_{g,2g-2}$. The value of $B_{g,2g-2}$ has been determined in an earlier work. One may interpret this formula in terms of the relationship between the Quillen and Faltings metrics on the determinant of cohomology.

  
  
  
• Spectral action for torsion with and without boundaries. (arXiv:1008.3630v2 [hep-th] UPDATED)
  

  We derive a commutative spectral triple and study the spectral action for a rather general geometric setting which includes the (skew-symmetric) torsion and the chiral bag conditions on the boundary. The spectral action splits into bulk and boundary parts. In the bulk, we clarify certain issues of the previous calculations, show that many terms in fact cancel out, and demonstrate that this cancellation is a result of the chiral symmetry of spectral action. On the boundary, we calculate several leading terms in the expansion of spectral action in four dimensions for vanishing chiral parameter $\theta$ of the boundary conditions, and show that $\theta=0$ is a critical point of the action in any dimension and at all orders of the expansion.

  
  
  
• Superconductivity in the two-dimensional Hubbard model based on the exact pair potential. (arXiv:1008.5116v2 [cond-mat.supr-con] UPDATED)
  

  We analyze solutions to a superconducting gap equation based on the two-dimensional Hubbard model with nearest and next-to-nearest neighbor hopping. The Cooper pair potential can be calculated exactly and expressed in terms of elliptic functions. The Fermi surfaces at finite temperature and chemical potential are calculated based on the exact two-body S-matrix of the Hubbard model using the formalism we recently developed, which allows variation of hole doping. The resulting solutions to the gap equation are strongly anisotropic, namely largest in the anti-nodal direction, and zero in the nodal directions of the Brillouin zone. For U/t = 13 and t' /t =-0.3, appropriate to BSCO, and a physically natural choice for the cut-off, our self-contained analytic calculations yield the gap in the anti-nodal direction Delta/t = 0.06 and a maximum Tc/t = 0.04 at hole doping h=0.15. For phenomenological fits to the Fermi surfaces for cuprates, we obtain the comparable value Tc/t = 0.03 at optimal doping, both in good agreement with experiments. The superconducting gap is non-zero for all hole-doping h < 0.35, and increases all the way down to zero doping, suggesting that it evolves into the pseudogap.

  
  
  
• An Alternative to Decoherence by Environment and the Appearance of a Classical World. (arXiv:1009.1220v1 [quant-ph] CROSS LISTED)
  

  We provide an alternative approach to the decoherence-by-environment paradigm in the field of the quantum measurement process and the appearance of a classical world. In contrast to the decoherence approach we argue that the transition from pure states to mixtures and the appearance of macro objects (and macroscopic properties) can be understood without invoking the measurement-like influence of the environment on the pointer-states of the measuring instrument. We show that every generic many-body system contains within the class of microscopic quantum observables a subalgebra of macro observables, the spectrum of which comprises the macroscopic properties of the many-body system. Our analysis is based (among other things) on two ingenious papers by v.Neumann and v.Kampen.

  
  
  
• Higher-Order-Schmidt-Representations and their Relevance for the Basis-Ambiguity. (arXiv:1009.1223v1 [quant-ph] CROSS LISTED)
  

  With the help of a useful mathematical tool, the polar decomposition of closed operators, and a simple observation, i.e. the unique relation between tensor-product states and compact operators, we manage to give a compact and coherent account of the various properties of higher-order-Schmidt-representations.