arXiv subjects

Duccio Pappadopulo

Publications and source records attributed to Duccio Pappadopulo.

At least 37 records · Page 2Linked to original sources

arXiv2015

Radiative PQ Breaking and the Higgs Boson Mass

The small and negative value of the Standard Model Higgs quartic coupling at high scales can be understood in terms of anthropic selection on a landscape where large and negative values are favored: most universes have a very short-lived electroweak vacuum and typical observers are in universes close to the corresponding metastability boundary. We provide a simple example of such a landscape with a Peccei-Quinn symmetry breaking scale generated through dimensional transmutation and supersymmetry softly broken at an intermediate scale. Large and negative contributions to the Higgs quartic are typically generated on integrating out the saxion field. Cancellations among these contributions are forced by the anthropic requirement of a sufficiently long-lived electroweak vacuum, determining the multiverse distribution for the Higgs quartic in a similar way to that of the cosmological constant. This leads to a statistical prediction of the Higgs boson mass that, for a wide range of parameters, yields the observed value within the 1$σ$ statistical uncertainty of $\sim$ 5 GeV originating from the multiverse distribution. The strong CP problem is solved and single-component axion dark matter is predicted, with an abundance that can be understood from environmental selection. A more general setting for the Higgs mass prediction is discussed.

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arXiv2015

OPE Convergence in Conformal Field Theory

We clarify questions related to the convergence of the OPE and conformal block decomposition in unitary Conformal Field Theories (for any number of spacetime dimensions). In particular, we explain why these expansions are convergent in a finite region. We also show that the convergence is exponentially fast, in the sense that the operators of dimension above Delta contribute to correlation functions at most exp(-a Delta). Here the constant a>0 depends on the positions of operator insertions and we compute it explicitly.

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arXiv2015

Multiverse Dark Matter: SUSY or Axions

The observed values of the cosmological constant {\it and} the abundance of Dark Matter (DM) can be successfully understood, using certain measures, by imposing the anthropic requirement that density perturbations go non-linear and virialize to form halos. This requires a probability distribution favoring low amounts of DM, i.e. low values of the PQ scale $f$ for the QCD axion and low values of the superpartner mass scale $\tilde{m}$ for LSP thermal relics. In theories with independent scanning of multiple DM components, there is a high probability for DM to be dominated by a single component. For example, with independent scanning of $f$ and $\tilde{m}$, TeV-scale LSP DM and an axion solution to the strong CP problem are unlikely to coexist. With thermal LSP DM, the scheme allows an understanding of a Little SUSY Hierarchy with multi-TeV superpartners. Alternatively, with axion DM, PQ breaking before (after) inflation leads to $f$ typically below (below) the projected range of the current ADMX experiment of $f = (3 - 30) \times 10^{11}$ GeV, providing strong motivation to develop experimental techniques for probing lower $f$.

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arXiv2014

Heavy Vector Triplets: Bridging Theory and Data

We introduce a model-independent strategy to study narrow resonances which we apply to a heavy vector triplet of the Standard Model (SM) group for illustration. The method is based on a simplified phenomenological Lagrangian which reproduces a large class of explicit models. Firstly, this allows us to derive robust model-independent phenomenological features and, conversely, to identify the peculiarities of different explicit realizations. Secondly, limits on cross-section times BR can be converted into bounds on a few relevant parameters in a fully analytic way, allowing for an interpretation in any given explicit model. Based on the available 8 TeV LHC analyses, we derive current limits and interpret them for vector triplets arising in weakly coupled (gauge) and strongly coupled (composite) extensions of the SM. We point out that a model-independent limit setting procedure must be based on purely on-shell quantities, like a cross-section times BR. Finite width effects altering the limits can be considerably reduced by focusing on the on-shell signal region. We illustrate this aspect with a study of the invariant mass distribution in di-lepton searches and the transverse mass distribution in lepton-neutrino final states. In addition to this paper we provide a set of online tools available at a dedicated webpage.

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arXiv2014

A modified naturalness principle and its experimental tests

Motivated by LHC results, we modify the usual criterion for naturalness by ignoring the uncomputable power divergences. The Standard Model satisfies the modified criterion ('finite naturalness') for the measured values of its parameters. Extensions of the SM motivated by observations (Dark Matter, neutrino masses, the strong CP problem, vacuum instability, inflation) satisfy finite naturalness in special ranges of their parameter spaces which often imply new particles below a few TeV. Finite naturalness bounds are weaker than usual naturalness bounds because any new particle with SM gauge interactions gives a finite contribution to the Higgs mass at two loop order.

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arXiv2014

Strong Higgs Interactions at a Linear Collider

We study the impact of Higgs precision measurements at a high-energy and high-luminosity linear electron positron collider, such as CLIC or the ILC, on the parameter space of a strongly interacting Higgs boson. Some combination of anomalous couplings are already tightly constrained by current fits to electroweak observables. However, even small deviations in the cross sections of single and double Higgs production, or the mere detection of a triple Higgs final state, can help establish whether it is a composite state and whether or not it emerges as a pseudo-Nambu-Goldstone boson from an underlying broken symmetry. We obtain an estimate of the ILC and CLIC sensitivities on the anomalous Higgs couplings from a study of WW scattering and hh production which can be translated into a sensitivity on the compositeness scale 4πf, or equivalently on the degree of compositeness ξ=v^2/f^2. We summarize the current experimental constraints, from electroweak data and direct resonance searches, and the expected reach of the LHC and CLIC on ξand on the scale of the new resonances.

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arXiv2013

A naturally light dilaton

Goldstone's theorem does not apply straightforwardly to the case of spontaneously broken scale invariance. We elucidate under what conditions a light scalar degree of freedom, identifiable with the dilaton, can naturally arise. Our construction can be considered an explicit dynamical solution to the cosmological constant problem in the scalar version of gravity.

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arXiv2013

Physics at the CLIC e+e- Linear Collider -- Input to the Snowmass process 2013

This paper summarizes the physics potential of the CLIC high-energy e+e- linear collider. It provides input to the Snowmass 2013 process for the energy-frontier working groups on The Higgs Boson (HE1), Precision Study of Electroweak Interactions (HE2), Fully Understanding the Top Quark (HE3), as well as The Path Beyond the Standard Model -- New Particles, Forces, and Dimensions (HE4). It is accompanied by a paper describing the CLIC accelerator study, submitted to the Frontier Capabilities group of the Snowmass process.

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arXiv2013

On the effect of resonances in composite Higgs phenomenology

We consider a generic composite Higgs model based on the coset SO(5)/SO(4) and study its phenomenology beyond the leading low-energy effective lagrangian approximation. Our basic goal is to introduce in a controllable and simple way the lowest-lying, possibly narrow, resonances that may exist is such models. We do so by proposing a criterion that we call partial UV completion. We characterize the simplest cases, corresponding respectively to a scalar in either singlet or tensor representation of SO(4) and to vectors in the adjoint of SO(4). We study the impact of these resonances on the signals associated to high-energy vector boson scattering, pointing out for each resonance the characteristic patterns of depletion and enhancement with respect to the leading-order chiral lagrangian. En route we derive the O(p^4) general chiral lagrangian and discuss its peculiar accidental and approximate symmetries.

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arXiv2013

A minimally tuned composite Higgs model from an extra dimension

We construct and study the 5D realization of a composite Higgs model with minimal tuning. The Higgs is a (pseudo-)Goldstone boson from the spontaneous breaking of a global SO(5) symmetry to an SO(4) subgroup. The peculiarity of our construction lies in the specific choice of the SO(5) representations of the 5D fermions from which the Standard Model fields arise as chiral zero modes. This choice reduces the tuning of these models to the minimal model-independent value allowed by electroweak precision tests. We analyse the main differences between our 5D construction and other descriptions in terms of purely 4D field theories. 5D models are generally more constrained and show a generic difficulty in accommodating a light Higgs without reintroducing large corrections to the \hat{S} parameter. We propose a specific construction in which this tension can be, even though accidentally, relaxed. We discuss the spectrum of the top partners in the viable regions of parameter space and predict the existence of light exotic quarks, Υ, of charge 8/3 whose striking decay channel Υ\to W^+W^+W^+ b can lead to either exclusion or confirmation of the model in the near future.

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arXiv2012

On Partial Compositeness and the CP asymmetry in charm decays

Recently, the LHCb and CDF collaborations reported the measure of an unexpectedly large direct CP asymmetry in D meson decays. In this paper we ask if new physics associated with Partial Compositeness could plausibly explain this result. We find that Composite Higgs models with mass scale around 10 TeV can account for it, while marginally satisfying all other flavor constraints in the quark sector. The minimal framework is however inadequate in the lepton sector due to the strong constraint from μ to e γ. This tension can be efficiently alleviated by realizing Partial Compositeness within Supersymmetry. The resulting models can saturate the CP asymmetry in D decays for superpartner masses close to the TeV scale and somewhat large A-terms. The supersymmetric realization of Partial Compositeness also offers a predictive and phenomenologically viable organizing principle for R-Parity violation, and may result in very distinctive signatures at hadron colliders. With or without Supersymmetry, the neutron EDM is expected to be around the present experimental sensitivity.

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arXiv2012

Implications of XENON100 and LHC results for Dark Matter models

We perform a fit to the recent Xenon100 data and study its implications for Dark Matter scenarios. We find that Inelastic Dark Matter is disfavoured as an explana- tion to the DAMA/LIBRA annual modulation signal. Concerning the scalar singlet DM model, we find that the Xenon100 data disfavors its constrained limit. We study the CMSSM as well as the low scale phenomenological MSSM taking into account latest Tevatron and LHC data (1.1/fb) about sparticles and Bs \rightarrow μμ. After the EPS 2011 conference, LHC excludes the "Higgs-resonance" region of DM freeze-out and Xenon100 disfavors the "well-tempered" bino/higgsino, realized in the "focus-point" region of the CMSSM parameter space. The preferred region shifts to heavier sparticles, higher fine-tuning, higher tan β and the quality of the fit deteriorates.

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arXiv2011

Strong, weak and flavor scalar triplets for the CDF Wjj anomaly

A model describing the 4.1σ Wjj anomaly observed by the CDF experiment at the Tevatron collider is introduced. It features new scalar particles which are charged both under the SU(3)_C and the SU(2)_L gauge groups and which couple to pairs of quarks. We introduce several identical replicas of the scalar multiplets in order to leave an unbroken U(3)_Q x U(3)_U x U(3)_D flavor symmetry to satisfy the constraints coming from flavor physics. We discuss the LHC reach on the new scalar resonances both in the resonant production channel (with the Wjj final state) and in the QCD pair production channel (with the 4j final state).

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arXiv2011

Can CoGeNT and DAMA Modulations Be Due to Dark Matter?

We explore the dark matter interpretation of the anomalies claimed by the DAMA and CoGeNT experiments, in conjunction with the various null direct-detection experiments. An independent analysis of the CoGeNT data is employed and several experimental and astrophysical uncertainties are considered. Various phenomenological models are studied, including isospin violating interactions, momentum-dependent form factors, velocity-dependent form factors, inelastic scatterings (endothermic and exothermic) and channeling. We find that the severe tension between the anomalies and the null results can be ameliorated but not eliminated, unless extreme assumptions are made.

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arXiv2011

Lopsided Gauge Mediation

It has been recently pointed out that the unavoidable tuning among supersymmetric parameters required to raise the Higgs boson mass beyond its experimental limit opens up new avenues for dealing with the so called $μ$-$B_μ$ problem of gauge mediation. In fact, it allows for accommodating, with no further parameter tuning, large values of $B_μ$ and of the other Higgs-sector soft masses, as predicted in models where both $μ$ and $B_μ$ are generated at one-loop order. This class of models, called Lopsided Gauge Mediation, offers an interesting alternative to conventional gauge mediation and is characterized by a strikingly different phenomenology, with light higgsinos, very large Higgs pseudoscalar mass, and moderately light sleptons. We discuss general parametric relations involving the fine-tuning of the model and various observables such as the chargino mass and the value of $\tanβ$. We build an explicit model and we study the constraints coming from LEP and Tevatron. We show that in spite of new interactions between the Higgs and the messenger superfields, the theory can remain perturbative up to very large scales, thus retaining gauge coupling unification.

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arXiv2010

A Non Standard Supersymmetric Spectrum

Taking a bottom-up point of view and focussing on the lack of signals so far in the Higgs and in the flavour sectors, we argue in favour of giving consideration to supersymmetric extensions of the Standard Model where the lightest Higgs boson has a mass between 200 and 300 GeV and the first two generations of s-fermions are above 20 TeV. After examining the simplest extensions of the Minimal Supersymmetric Standard Model that allow this in a natural way, we summarize the main consequences of this pattern of masses at the LHC and we analyze the consequences of a heavier than normal Higgs boson for Dark Matter.

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arXiv2010

T-parity, its problems and their solution

We point out a basic difficulty in the construction of little-Higgs models with T-parity which is overlooked by large part of the present literature. Almost all models proposed so far fail to achieve their goal: they either suffer from sizable electroweak corrections or from a breakdown of collective breaking. We provide a model building recipe to bypass the above problem and apply it to build the simplest T-invariant extension of the Littlest Higgs. Our model predicts additional T-odd pseudo-Goldstone bosons with weak scale masses.

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arXiv2010

Minimal Matter at the Large Hadron Collider

We classify all possible new U(1) x SU(2) x SU(3) multiplets that can couple to pairs of SM particles. Assuming that production of such new particles is dominated by their gauge interactions we study their signals at LHC, finding the following five main classes: i) lepto-quark 2l 2q signals; ii) di-lepton 4l signals; iii) di-quarks 4j signals, iv) heavy-lepton 2l 2V signals and v) heavy quarks 2j 2V signals, where V denotes heavy SM vectors (with W being associated to exotic fermions). In each case we outilne the most promising final states, the SM backgrounds and propose the needed searches.

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