Search

We show that if dark matter consists of QCD axions in the post-inflationary scenario more than ten percent of it efficiently collapses into Bose stars at matter-radiation equality. Such a result is mostly independent of the present uncertainties on the axion mass. This large population of solitons, with asteroid masses and Earth-Moon distance sizes, might plausibly survive until today, with potentially interesting implications for phenomenology and experimental searches., Comment: 23 pages + appendices

We strengthen the cosmological bound on the axion mass, by solving the momentum-dependent Boltzmann equations for axion-pion scatterings and by using a phenomenological production rate derived from pion-pion scattering data, overcoming the breakdown of chiral perturbation theory. Using present cosmological datasets we obtain $m_a\leq 0.24~\text{eV}$. To further improve the bound and exploit the reach of upcoming cosmological surveys, reliable non-perturbative calculations above the QCD crossover are needed., Comment: 6+8 pages, 7 figures

We study the contribution to the QCD axion dark matter abundance that is produced by string defects during the so-called scaling regime. Clear evidence of scaling violations is found, the most conservative extrapolation of which strongly suggests a large number of axions from strings. In this regime, nonlinearities at around the QCD scale are shown to play an important role in determining the final abundance. The overall result is a lower bound on the QCD axion mass in the post-inflationary scenario that is substantially stronger than the naive one from misalignment., Comment: 19 pages + appendices

We extend the study of the two-dimensional euclidean $\phi^4$ theory initiated in ref. [1] to the $\mathbb Z_2$ broken phase. In particular, we compute in perturbation theory up to N$^4$LO in the quartic coupling the vacuum energy, the vacuum expectation value of $\phi$ and the mass gap of the theory. We determine the large order behavior of the perturbative series by finding the leading order finite action complex instanton configuration in the $\mathbb Z_2$ broken phase. Using an appropriate conformal mapping, we then Borel resum the perturbative series. Interestingly enough, the truncated perturbative series for the vacuum energy and the vacuum expectation value of the field is reliable up to the critical coupling where a second order phase transition occurs, and breaks down around the transition for the mass gap. We compute the vacuum energy using also an alternative perturbative series, dubbed exact perturbation theory, that allows us to effectively reach N$^8$LO in the quartic coupling. In this way we can access the strong coupling region of the $\mathbb Z_2$ broken phase and test Chang duality by comparing the vacuum energies computed in three different descriptions of the same physical system. This result can also be considered as a confirmation of the Borel summability of the theory. Our results are in very good agreement (and with comparable or better precision) with those obtained by Hamiltonian truncation methods. We also discuss some subtleties related to the physical interpretation of the mass gap and provide evidence that the kink mass can be obtained by analytic continuation from the unbroken to the broken phase., Comment: v1: 36 pages, 11 figures, 8 tables; v2: 37 pages, 12 figures, 8 tables. Added figure 12, minor improvements, typos fixed, matches JHEP version

We improve the precision of the topological susceptibility of QCD, and therefore of the QCD axion mass, by including $O(\alpha_{\rm em})$ and NNLO corrections in the chiral expansion, which amount to 0.65(21)% and -0.71(29)% respectively. Both corrections are one order of magnitude smaller than the known NLO ones, confirming the very good convergence of the chiral expansion and its reliability. Using the latest estimates for the light quark masses the current uncertainty is dominated by the one of the low-energy constant $\ell_7$. When combined with possible improvements on the light quark mass ratio and $\ell_7$ from lattice QCD, our computation could allow to determine the QCD axion mass with per-mille accuracy., Comment: 19 pages, 1 figure

We study the system of axion strings that forms in the early Universe if the Peccei-Quinn symmetry is restored after inflation. Using numerical simulations, we establish the existence of an asymptotic solution to which the system is attracted independently of the initial conditions. We study in detail the properties of this solution, including the average number of strings per Hubble patch, the distribution of loops and long strings, the way that different types of radiation are emitted, and the shape of the spectrum of axions produced. We find clear evidence of logarithmic violations of the scaling properties of the attractor solution. We also find that, while most of the axions are emitted with momenta of order Hubble, most of the axion energy density is contained in axions with energy of order the string core scale, at least in the parameter range available in the simulation. While such a spectrum would lead to a negligible number density of relic axions from strings when extrapolated to the physical parameter region, we show that the presence of small logarithmic corrections to the spectrum shape could completely alter such a conclusion. A detailed understanding of the evolution of the axion spectrum is therefore crucial for a reliable estimate of the relic axion abundance from strings., Comment: 58 pages, 23 of appendices

Perturbation theory of a large class of scalar field theories in $d<4$ can be shown to be Borel resummable using arguments based on Lefschetz thimbles. As an example we study in detail the $\lambda \phi^4$ theory in two dimensions in the $Z_2$ symmetric phase. We extend the results for the perturbative expansion of several quantities up to N$^8$LO and show how the behavior of the theory at strong coupling can be recovered successfully using known resummation techniques. In particular, we compute the vacuum energy and the mass gap for values of the coupling up to the critical point, where the theory becomes gapless and lies in the same universality class of the 2d Ising model. Several properties of the critical point are determined and agree with known exact expressions. The results are in very good agreement (and with comparable precision) with those obtained by other non-perturbative approaches, such as lattice simulations and Hamiltonian truncation methods., Comment: v1: 36 pages, 9 figures, 10 tables; v2: computed one more perturbative coefficient, minor improvements, matches JHEP version

We study quantum mechanical systems with a discrete spectrum. We show that the asymptotic series associated to certain paths of steepest-descent (Lefschetz thimbles) are Borel resummable to the full result. Using a geometrical approach based on the Picard-Lefschetz theory we characterize the conditions under which perturbative expansions lead to exact results. Even when such conditions are not met, we explain how to define a different perturbative expansion that reproduces the full answer without the need of transseries, i.e. non-perturbative effects, such as real (or complex) instantons. Applications to several quantum mechanical systems are presented., Comment: v1: 42 pages, 8 figures; v2: 43 pages, 9 figures, minor improvements and references added, matches JHEP published version; v3: minor corrections and references added

The properties of the QCD axion are strictly related to the dependence of strong interactions on the topological parameter theta. We present a determination of the topological properties of QCD for temperatures up to around 600 MeV, obtained by lattice QCD simulations with 2+1 flavors and physical quark masses. Numerical results for the topological susceptibility, when compared to instanton gas computations, differ both in size and in the temperature dependence. We discuss the implications of such findings for axion phenomenology, also in comparison to similar studies in the literature, and the prospects for future investigations., Comment: Invited talk at XII Quark Confinement, 29 August - 3 September, 2016, Thessaloniki, Greece, 9 pages, 6 figures

In quantum mechanics and quantum field theory perturbation theory generically requires the inclusion of extra contributions non-perturbative in the coupling, such as instantons, to reproduce exact results. We show how full non-perturbative results can be encoded in a suitable modified perturbative series in a class of quantum mechanical problems. We illustrate this explicitly in examples which are known to contain non-perturbative effects, such as the (supersymmetric) double-well potential, the pure anharmonic oscillator, and the perturbative expansion around a false vacuum., Comment: 4 pages, 1 figure; v2: minor corrections and improvements, ref. added

We investigate the topological properties of $N_f = 2+1$ QCD with physical quark masses, both at zero and finite temperature. We adopt stout improved staggered fermions and explore a range of lattice spacings $a \sim 0.05 - 0.12$ fm. At zero temperature we estimate both finite size and finite cut-off effects, comparing our continuum extrapolated results for the topological susceptibility $\chi$ with predictions from chiral perturbation theory. At finite temperature, we explore a region going from $T_c$ up to around $4\, T_c$, where we provide continuum extrapolated results for the topological susceptibility and for the fourth moment of the topological charge distribution. While the latter converges to the dilute instanton gas prediction the former differs strongly both in the size and in the temperature dependence. This results in a shift of the axion dark matter window of almost one order of magnitude with respect to the instanton computation., Comment: 24 pages, 12 figures, 5 tables, final version published in JHEP

We show how several properties of the QCD axion can be extracted at high precision using only first principle QCD computations. By combining NLO results obtained in chiral perturbation theory with recent Lattice QCD results the full axion potential, its mass and the coupling to photons can be reconstructed with percent precision. Axion couplings to nucleons can also be derived reliably, with uncertainties smaller than ten percent. The approach presented here allows the precision to be further improved as uncertainties on the light quark masses and the effective theory couplings are reduced. We also compute the finite temperature dependence of the axion potential and its mass up to the crossover region. For higher temperature we point out the unreliability of the conventional instanton approach and study its impact on the computation of the axion relic abundance., Comment: 38 pages, 6 figures. v2: Discussion in sec. 2.4 simplified, fig.6 corrected, published version

We present the state-of-the-art of the effective field theory computation of the MSSM Higgs mass, improving the existing ones by including extra threshold corrections. We show that, with this approach, the theoretical uncertainty is within 1 GeV in most of the relevant parameter space. We confirm the smaller value of the Higgs mass found in the EFT computations, which implies a slightly heavier SUSY scale. We study the large tan(\beta) region, finding that sbottom thresholds might relax the upper bound on the scale of SUSY. We present SusyHD, a fast computer code that computes the Higgs mass and its uncertainty for any SUSY scale, from the TeV to the Planck scale, even in Split SUSY, both in the DRbar and in the on-shell schemes. Finally, we apply our results to derive bounds on some well motivated SUSY models, in particular we show how the value of the Higgs mass allows to determine the complete spectrum in minimal gauge mediation., Comment: 37 pages, 9 figures

We investigate the possible implications of the measured value of the scalar tilt $n_s$ for the tensor-to-scalar ratio $r$ in slow-roll, single-field inflationary models. The measured value of the tilt satisfies $n_s -1\sim 1/N_*$, where $N_* \sim 60$ is the number of $e$-folds for observationally relevant scales. If this is not a coincidence and the scaling holds for different values of $N$, it strongly suggests that either $r$ is as big as $10^{-1}$ (a possibility in tension with the recent data), or smaller than $10^{-2}$ and exponentially dependent on $n_s$. A large region of the ($n_s$,$r$) plane is not compatible with this scaling., Comment: 4 pages, 1 figure. Published version

Direct LHC bounds on colored SUSY particles now corner naturalness more than the measured value of the Higgs mass does. Bounds on the gluino are of particular importance, since it radiatively "sucks" up the stop and Higgs-up soft masses. As a result, even models that easily accommodate a 125 GeV Higgs are almost as tuned as the simplest version of SUSY, the MSSM: at best at the percent level. In this paper, we further examine how current LHC results constrain naturalness in three classes of models that may relax LHC bounds on sparticles: split families, baryonic RPV, and Dirac gauginos. In models of split families and bRPV, the bounds on the gluino are only slightly reduced, resulting in a few percent tuning. In particular, having a natural spectrum in bRPV models typically implies that tops, Ws, and Zs are easily produced in the cascade decays of squarks and gluinos. The resulting leptons and missing energy push the gluino mass limit above 1 TeV. Even when the gluino has a Dirac mass and does not contribute to the stop mass at one loop, tuning reappears in calculable models because there is no symmetry imposing the supersoft limit. We conclude that, even if sparticles are found at LHC-14, naturalness will not emerge triumphant., Comment: 22 pages, 6 figures, plus appendices

The lack of evidence for new physics beyond the standard model at the LHC points to a paucity of new particles near the weak scale. This suggests that the weak scale is tuned and that supersymmetry, if present at all, is realized at higher energies. The measured Higgs mass constrains the scalar sparticles to be below 10^5 TeV, while gauge coupling unification favors Higgsinos below 100 TeV. Nevertheless, in many models gaugino masses are suppressed and remain within reach of the LHC. Tuning the weak scale and the renormalization group evolution of the scalar masses constrain Split model building. Due to the small gaugino masses, either the squarks or the up-higgs often run tachyonic; in the latter case, successful electroweak breaking requires heavy higgsinos near the scalar sparticles. We discuss the consequences of tuning the weak scale and the phenomenology of several models of Split supersymmetry including anomaly mediation, U(1)_(B-L) mediation, and Split gauge mediation., Comment: 26 pages, 12 figures; v2:discussion and figure on the status of fine-tuning in SUSY added, pheno section extended

Light states associated with the hierarchy problem affect the Higgs LHC production and decays. We illustrate this within the MSSM and two simple extensions applying the latest bounds from LHC Higgs searches. Large deviations in the Higgs properties are expected in a natural SUSY spectrum. The discovery of a non-Standard-Model Higgs may signal the presence of light stops accessible at the LHC. Conversely, the more the Higgs is Standard-Model-like, the more tuned the theory becomes. Taking the ratio of different Higgs decay channels at the LHC cancels the leading QCD uncertainties and potentially improves the accuracy in Higgs coupling measurements to the percent level. This may lead to the possibility of doing precision Higgs physics at the LHC. Finally, we entertain the possibility that the ATLAS excess around 125 GeV persists with a Higgs production cross-section that is enhanced compared to the SM. This increase can only be accommodated in extensions of the MSSM and it may suggest that stops lie below 400 GeV, likely within reach of next year's LHC run., Comment: 22 pages, 14 figures. v2: lambdaSUSY point changed, typos fixed, references added, conclusions unchanged

It has recently been shown that in single field slow-roll inflation the total volume cannot grow by a factor larger than e^(S_dS/2) without becoming infinite. The bound is saturated exactly at the phase transition to eternal inflation where the probability to produce infinite volume becomes non zero. We show that the bound holds sharply also in any space-time dimensions, when arbitrary higher-dimensional operators are included and in the multi-field inflationary case. The relation with the entropy of de Sitter and the universality of the bound strengthen the case for a deeper holographic interpretation. As a spin-off we provide the formalism to compute the probability distribution of the volume after inflation for generic multi-field models, which might help to address questions about the population of vacua of the landscape during slow-roll inflation., Comment: 24 pages, 5 figures

We clarify a number of issues on Fayet-Iliopoulos (FI) terms in supergravity, keeping the formalism at a minumum and making use of explicit examples. We explain why, if the U(1) vector is massive everywhere in field space, FI terms are not genuine and can always be redefined away or introduced when they are not present. We formulate a simple anomaly-free model with a genuine FI term, a classically stable de Sitter (dS) vacuum and no global symmetries. We explore the relation between N=2 and N=1 FI terms by discussing N=1 truncations of N=2 models with classically stable dS vacua., Comment: 17 pages, no figures; v3: added sentence at the end of section 3.2

We study the possibility of gauging the Standard Model flavor group. Anomaly cancellation leads to the addition of fermions whose mass is inversely proportional to the known fermion masses. In this case all flavor violating effects turn out to be controlled roughly by the Standard Model Yukawa, suppressing transitions for the light generations. Due to the inverted hierarchy the scale of new gauge flavor bosons could be as low as the electroweak scale without violating any existing bound but accessible at the Tevatron and the LHC. The mechanism of flavor protection potentially provides an alternative to Minimal Flavor Violation, with flavor violating effects suppressed by hierarchy of scales rather than couplings., Comment: 24 pages + appendices; v2) Refs. added and numerical examples improved. Results unchanged; v3) small typos in appendix B corrected

We consider non-universal 'minimal' Z' models, whose additional U(1) charge is a non-anomalous linear combination of the weak hypercharge Y, the baryon number B and the partial lepton numbers (L_e, L_mu, L_tau), with no exotic fermions beyond three standard families with right-handed neutrinos. We show that the observed pattern of neutrino masses and mixing can be fully reproduced by a gauge-invariant renormalizable Lagrangian, and flavor-changing neutral currents in the charged lepton sector are suppressed by a GIM mechanism. We then discuss the phenomenology of some benchmark models. The electrophilic B-3L_e model is significantly constrained by electroweak precision tests, but still allows to fit the hint of an excess observed by CDF in dielectrons but not in dimuons. The muonphilic B-3L_mu model is very mildly constrained by electroweak precision tests, so that even the very early phase of the LHC can explore significant areas of parameter space. We also discuss the hadrophobic L_mu-L_tau model, which has recently attracted interest in connection with some puzzling features of cosmic ray spectra., Comment: 29 pages, 13 figures

We consider `minimal' Z' models, whose phenomenology is controlled by only three parameters beyond the Standard Model ones: the Z' mass and two effective coupling constants. They encompass many popular models motivated by grand unification, as well as many arising in other theoretical contexts. This parameterization takes also into account both mass and kinetic mixing effects, which we show to be sizable in some cases. After discussing the interplay between the bounds from electroweak precision tests and recent direct searches at the Tevatron, we extend our analysis to estimate the early LHC discovery potential. We consider a center-of-mass energy from 7 towards 10 TeV and an integrated luminosity from 50 to several hundred pb^-1, taking all existing bounds into account. We find that the LHC will start exploring virgin land in parameter space for M_Z' around 700 GeV, with lower masses still excluded by the Tevatron and higher masses still excluded by electroweak precision tests. Increasing the energy up to 10 TeV, the LHC will start probing a wider range of Z' masses and couplings, although several hundred pb^-1 will be needed to explore the regions of couplings favored by grand unification and to overcome the Tevatron bounds in the mass region around 250 GeV., Comment: 25 pages. v2: small improvements and minor corrections, version accepted for publication on JHEP

We establish the precise correspondence between Type-IIA flux compactifications preserving an exact or spontaneously broken N=4 supersymmetry in four dimensions, and gaugings of their effective N=4 supergravities. We exhibit the explicit map between fluxes and Bianchi identities in the higher-dimensional theory and generalized structure constants and Jacobi identities in the reduced theory, also detailing the origin of gauge groups embedded at angles in the duality group. We present AdS4 solutions of the massive Type-IIA theory with spontaneous breaking to N=1, at small string coupling and large volume, and discuss their dual CFT3., Comment: 43 pages, 1 figure. v2: refs added, v3: minor additions. Final version to appear on JHEP

We calculate the probability distribution for the volume of the Universe after slow-roll inflation both in the eternal and in the non-eternal regime. Far from the eternal regime the probability distribution for the number of e-foldings, defined as one third of the logarithm of the volume, is sharply peaked around the number of e-foldings of the classical inflaton trajectory. At the transition to the eternal regime this probability is still peaked (with the width of order one e-folding) around the average, which gets twice larger at the transition point. As one enters the eternal regime the probability for the volume to be finite rapidly becomes exponentially small. In addition to developing techniques to study eternal inflation, our results allow us to establish the quantum generalization of a recently proposed bound on the number of e-foldings in the non-eternal regime: the probability for slow-roll inflation to produce a finite volume larger than e^(S_dS/2), where S_dS is the de Sitter entropy at the end of the inflationary stage, is smaller than the uncertainty due to non-perturbative quantum gravity effects. The existence of such a bound provides a consistency check for the idea of de Sitter complementarity., Comment: 47 pages, 11 figures

Even if nothing but a light Higgs is observed at the LHC, suggesting that the Standard Model is unmodified up to scales far above the weak scale, Higgs physics can yield surprises of fundamental significance for cosmology. As has long been known, the Standard Model vacuum may be metastable for low enough Higgs mass, but a specific value of the decay rate holds special significance: for a very narrow window of parameters, our Universe has not yet decayed but the current inflationary period can not be future eternal. Determining whether we are in this window requires exquisite but achievable experimental precision, with a measurement of the Higgs mass to 0.1 GeV at the LHC, the top mass to 60 MeV at a linear collider, as well as an improved determination of alpha_s by an order of magnitude on the lattice. If the parameters are observed to lie in this special range, particle physics will establish that the future of our Universe is a global big crunch, without harboring pockets of eternal inflation, strongly suggesting that eternal inflation is censored by the fundamental theory. This conclusion could be drawn even more sharply if metastability with the appropriate decay rate is found in the MSSM, where the physics governing the instability can be directly probed at the TeV scale., Comment: 25 pages, 3 figures. v2: updated value of top mass, added references, JHEP published version

We derive new consistency conditions for string compactifications with generic fluxes (RR, NSNS, geometrical) and localized sources (D-branes, NS-branes, KK-monopoles). The constraints are all related by string dualities and share a common origin in M-theory. We also find new sources of instabilities. We discuss the importance of these conditions for the consistency of the effective action and for the study of interpolating solutions between vacua., Comment: 29 pages, 2 figures, v2: published version

It is well known that in Lorentz invariant quantum field theories in flat space the commutator of space-like separated local operators vanishes (microcausality). We provide two different arguments showing that this is a consequence of the causal structure of the classical theory, rather than of Lorentz invariance. In particular, microcausality holds in arbitrary curved space-times, where Lorentz invariance is explicitly broken by the background metric. As illustrated by an explicit calculation on a cylinder this property is rather non trivial at the level of Feynman diagrams., Comment: 21 pages, 4 figures

Exploiting the fact that Kaluza-Klein monopoles and the associated generalized orbifold planes are sources for geometrical fluxes, omega, we show that the standard constraint omega.omega=0, valid for superstring compactifications on twisted tori, can be consistently relaxed. This leads to novel possibilities for constructing superstring models with fluxes and localized sources, as well as for stabilizing moduli. This also explains the ten-dimensional origin of a family of N=4 gauged supergravities, whose interpretation in type-IIA orientifold compactifications was lacking., Comment: 12 pages

We show that in any model of non-eternal inflation satisfying the null energy condition, the area of the de Sitter horizon increases by at least one Planck unit in each inflationary e-folding. This observation gives an operational meaning to the finiteness of the entropy S_dS of an inflationary de Sitter space eventually exiting into an asymptotically flat region: the asymptotic observer is never able to measure more than e^(S_dS) independent inflationary modes. This suggests a limitation on the amount of de Sitter space outside the horizon that can be consistently described at the semiclassical level, fitting well with other examples of the breakdown of locality in quantum gravity, such as in black hole evaporation. The bound does not hold in models of inflation that violate the null energy condition, such as ghost inflation. This strengthens the case for the thermodynamical interpretation of the bound as conventional black hole thermodynamics also fails in these models, strongly suggesting that these theories are incompatible with basic gravitational principles., Comment: 33 pages, 8 figures

The long-distance effective field theory of our Universe--the Standard Model coupled to gravity--has a unique 4D vacuum, but we show that it also has a landscape of lower-dimensional vacua, with the potential for moduli arising from vacuum and Casimir energies. For minimal Majorana neutrino masses, we find a near-continuous infinity of AdS3xS1 vacua, with circumference ~20 microns and AdS3 length 4x10^25 m. By AdS/CFT, there is a CFT2 of central charge c~10^90 which contains the Standard Model (and beyond) coupled to quantum gravity in this vacuum. Physics in these vacua is the same as in ours for energies between 10^-1 eV and 10^48 GeV, so this CFT2 also describes all the physics of our vacuum in this energy range. We show that it is possible to realize quantum-stabilized AdS vacua as near-horizon regions of new kinds of quantum extremal black objects in the higher-dimensional space--near critical black strings in 4D, near-critical black holes in 3D. The violation of the null-energy condition by the Casimir energy is crucial for these horizons to exist, as has already been realized for analogous non-extremal 3D black holes by Emparan, Fabbri and Kaloper. The new extremal 3D black holes are particularly interesting--they are (meta)stable with an entropy independent of hbar and G_N, so a microscopic counting of the entropy may be possible in the G_N->0 limit. Our results suggest that it should be possible to realize the larger landscape of AdS vacua in string theory as near-horizon geometries of new extremal black brane solutions., Comment: 44 pages, 9 figures

We present the complete calculation of the SU(3)-breaking corrections to the hyperon vector form factors up to O(p^4) in the Heavy Baryon Chiral Perturbation Theory. Because of the Ademollo-Gatto theorem, at this order the results do not depend on unknown low energy constants and allow to test the convergence of the chiral expansion. We complete and correct previous calculations and find that O(p^3) and O(1/M_0) corrections are important. We also study the inclusion of the decuplet degrees of freedom, showing that in this case the perturbative expansion is jeopardized. These results raise doubts on the reliability of the chiral expansion for hyperons., Comment: 20 pages, 4 figures, v2: published version

We elucidate the structure of D terms in N=1 orientifold compactifications with fluxes. As a case study, we consider a simple orbifold of the type-IIA theory with D6-branes at angles, O6-planes and general NSNS, RR and Scherk-Schwarz geometrical fluxes. We examine in detail the emergence of D terms, in their standard supergravity form, from an appropriate limit of the D-brane action. We derive the consistency conditions on gauged symmetries and general fluxes coming from brane-localized Bianchi identities, and their relation with the Freed-Witten anomaly. We extend our results to other N=1 compactifications and to non-geometrical fluxes. Finally, we discuss the possible role of U(1) D terms in the stabilization of the untwisted moduli from the closed string sector., Comment: 1+31 pages, 1 figure

We use chiral perturbation theory to investigate twisted and partially twisted boundary conditions which allow access to momenta other than integer multiples of 2pi/L on a lattice with spatial volume L^3. For K -> pi pi decays we show that the breaking of isospin symmetry by the twisted boundary conditions implies that the amplitudes cannot be determined in general. We find numerical evidence for the result that the finite volume effects of the boundary conditions are exponentially suppressed for quantities without final state interactions (meson masses and meson-to-vacuum matrix elements) in a simulation with partial twisting on a sea of N_f=2 non-perturbatively improved Wilson quarks., Comment: Talk presented at Lattice 2005 (Weak matrix elements), 6 pages, 1 figure

We introduce a new mechanism for producing locally stable de-Sitter or Minkowski vacua, with spontaneously broken N=1 supersymmetry and no massless scalars, applicable to superstring and M-theory compactifications with fluxes. We illustrate the mechanism with a simple N=1 supergravity model that provides parametric control on the sign and the size of the vacuum energy. The crucial ingredient is a gauged U(1) that involves both an axionic shift and an R-symmetry, and severely constrains the F- and D-term contributions to the potential., Comment: 4 pages, 1 figure, v3: published version

We present the results of the calculation of the Kl3 semileptonic form factor at zero momentum transfer, f(0), obtained at one-loop in partially quenched Chiral Perturbation Theory (with either Nf=2, or Nf=3, and with generic valence and sea quark masses). We show that for Nf=2, when the masses of the valence and sea light quarks are equal, the correction is of the order (MK^2-Mpi^2)^3. The formulae presented here can be useful for the mass extrapolation of the results obtained in lattice simulations to the physical point., Comment: 7 pages

We consider N=1 compactifications of the type-IIA theory on the T6/(Z2xZ2) orbifold and O6 orientifold, in the presence of D6-branes and general NSNS, RR and Scherk-Schwarz geometrical fluxes. Introducing a suitable dual formulation of the theory, we derive and solve the Bianchi identities, and show how certain combinations of fluxes can relax the constraints on D6-brane configurations coming from the cancellation of RR tadpoles. We then compute, via generalized dimensional reduction, the N=1, D=4 effective potential for the seven main moduli, and comment on the relation with truncated N=4 gaugings. As a byproduct, we obtain a general geometrical expression for the superpotential. We finally identify a family of fluxes, compatible with all Bianchi identities, that perturbatively stabilize all seven moduli in supersymmetric AdS4., Comment: 19 pages, no figures, JHEP3 LaTeX. Published version

We compute the 1-loop chiral corrections to the bag parameters which are needed for the discussion of the SUSY K-Kbar mixing problem in both finite and infinite volume. We then show how the bag parameters can be combined among themselves and with some auxiliary quantities and thus sensibly reduce the systematic errors due to chiral extrapolations as well as those due to finite volume artefacts present in the results obtained from lattice QCD. We also show that in some cases these advantages remain as such even after including the 2-loop chiral corrections. Similar discussion is also made for the K --> pi electro-weak penguin operators., Comment: 13 pages, 3 figures [added 1 reference and a discussion about the impact of the NNLO chiral corrections to the "golden ratios" (c.f. Sec.6)]

We construct new N=6 gauged supergravities in four and five dimensions using generalized dimensional reduction. Supersymmetry is spontaneously broken to N=4,2,0 with vanishing cosmological constant. We discuss the gaugings of the broken phases, the scalar geometries and the spectrum. Generalized orbifold reduction is also considered and an N=3 no-scale model is obtained with three independent mass parameters., Comment: 1+9 pages, accepted for publication in Physics Letters B

We consider the generalized dimensional reduction of pure ungauged N=4, D=5 supergravity, where supersymmetry is spontaneously broken to N=2 or N=0 with identically vanishing scalar potential. We explicitly construct the resulting gauged D=4 theory coupled to a single vector multiplet, which provides the minimal N=4 realization of a no-scale model. We discuss its relation with the standard classification of N=4 gaugings, extensions to non-compact twists and to higher dimensions, the N=2 theories obtained via consistent Z_2 orbifold projections and prospects for further generalizations., Comment: 1+28 pages, no figures, JHEP3 LaTeX, published version

We discuss the finite volume corrections to fK and BK by using the one-loop chiral perturbation theory in full, quenched, and partially quenched QCD. We show that the finite volume corrections to these quantities dominate the physical (infinite volume) chiral logarithms., Comment: 16 pages, 3 figures [published version]