HEP Phenomenology·hep-ph

Fri·Jun 2, 2017Friday·June 2, 2017

18 papers—13 primary·5 cross-listed·reconstructed*

01*
Linking LFV Higgs decays $h \to ℓ_{i} ℓ_{j}$ with CP violation in multi-scalar models
E. Barradas-Guevara🇲🇽 · J. Lorenzo Diaz-Cruz🇲🇽 · O. Felix-Beltran🇲🇽 · U. J. Saldana-Salazar🇲🇽
The study of LFV decays of the Higgs boson, $h \to ℓ_{i} ℓ_{j}$ , has become an active research subject both from the experimental and theoretical points of view. Such decays vanish within the SM and are highly suppressed in several theoretical extensions. Due to its relevance and relative simplicity to reconstruct the signal at future colliders, it is an important tool to probe SM extensions where it could reach detectable levels. Here we identify a mechanism that induces LFV Higgs interactions, by linking it with the appearance of CP violation in the scalar sector, within the context of general multi-Higgs models. We then focus on the simplest model of this type to study its phenomenology. The scalar sector of this minimal model consisting of a Higgs doublet and a Froggatt--Nielsen (FN) (complex) singlet is studied thoroughly, including the scalar spectrum and the Yukawa interactions. Constraints on the parameters of the model are derived from low-energy observables and LHC Higgs data, which is then applied to study the resulting predicted rates for the decay $h \to τ μ$ . Overall, branching ratios for $h \to τ μ$ of the order $1 0^{- 3}$ are obtained within this approach consistent with all known constraints.
hep-phhep-ex7 citations
02*
Inelastic cross-section and Survival Probabilities at LHC in mini-jet models
Daniel A. Fagundes🇧🇷 · Agnes Grau🇪🇸 · Giulia Pancheri🇮🇹 · Olga Shekhovtsova🇵🇱 · Yogendra N. Srivastava🇮🇹
Recent results for the total and inelastic hadronic cross-sections from LHC experiments are compared with predictions from a single channel PDF driven eikonal mini-jet model and from an empirical model. The role of soft gluon resummation in the infrared region in taming the rise of mini-jets and their contribution to the increase of the total cross-sections at high energies are discussed. Survival probabilities at LHC, whose theoretical estimates range from circa 10 percent to a few per mille, will be estimated in this model and compared with results from QCD inspired models and from multi channel eikonal models. We revisit a previous calculation and examine the origin of these discrepancies.
hep-phPRD(2017)·12 citations
03*
Antiproton--proton annihilation into light neutral meson pairs within an effective meson theory
Ying Wang🇫🇷 · Yury M. Bystritskiy🇷🇺 · Azad I. Ahmadov🇷🇺 · Egle Tomasi Gustafsson🇫🇷
Antiproton--proton annihilation into light neutral mesons in the few GeV energy domain is investigated in view of a global description of the existing data and predictions for future experiments at PANDA, FAIR. An effective meson model earlier developed, with mesonic and baryonic degrees of freedom in $s$ , $t$ , and $u$ channels, is applied here to $π^{0} π^{0}$ production. Form factors with logarithmic $s$ and $t (u)$ dependencies are applied. A fair agreement with the existing angular distributions is obtained. Applying SU(3) symmetry, it is straightforward to recover the angular distributions for $π^{0} η$ , and $η η$ production in the same energy range. A good agreement is generally obtained with all existing data.
hep-phPRC(2017)·2 citations
04*
Generalized Bottom-Tau unification, neutrino oscillations and dark matter: predictions from a lepton quarticity flavor approach
Salvador Centelles Chuliá🇪🇸 · Rahul Srivastava🇪🇸 · José W. F. Valle🇪🇸
We propose an $A_{4}$ extension of the Standard Model with a Lepton Quarticity symmetry correlating dark matter stability with the Dirac nature of neutrinos. The flavor symmetry predicts (i) a generalized bottom-tau mass relation involving all families, (ii) small neutrino masses are induced a la seesaw, (iii) CP must be significantly violated in neutrino oscillations, (iv) the atmospheric angle $θ_{23}$ lies in the second octant, and (v) only the normal neutrino mass ordering is realized.
hep-phhep-exPLB(2017)·73 citations
05*
Anomalous mass dimensions and Schwinger-Dyson equations boundary condition
A. Doff🇧🇷 · A. A. Natale🇧🇷
Theories with large mass anomalous dimensions ( $γ_{m}$ ) have been extensively studied because of their deep consequences for models where the scalar bosons are composite. Large $γ_{m}$ values may appear when a non-Abelian gauge theory has a large number of fermions or is affected by four-fermion interactions. In this note we provide a simple explanation how $γ_{m}$ can be directly read out from the IR and UV boundary conditions derived from the gap equation, and verify that moderate $γ_{m}$ values appear when the theory possess a large number of fermions, but large $γ_{m}$ values are obtained only when four-fermion interactions are added to the theory. We also verify how the critical line separating the different chiral phases emerge from these conditions.
hep-phhep-latPLB(2017)·4 citations
06*
Effective action for reggeized gluons, classical gluon field of relativistic color charge and color glass condensate approach
S. Bondarenko🇮🇱 · L. Lipatov🇷🇺 · A. Prygarin🇮🇱
We discuss application of formalism of small- $x$ effective action for reggeized gluons, \cite{Gribov,LipatovEff,BFKL}, for the calculation of classical gluon field of relativistic color charge, similarly to that done in CGC approach of \cite{Venug,Kovner}. The equations of motion with the reggeon fields are solved in LO and NLO approximations and new solutions are found. The results are compared to the calculations performed in the CGC framework and it is demonstrated that the LO CGC results for the classical field are reproduced in our calculations. Possible applications of the NLO solution in the effective action and CGC frameworks are discussed as well.
hep-phhep-thEPJC(2017)·30 citations
07*
Reconciling EFT and hybrid calculations of the light MSSM Higgs-boson mass
Henning Bahl🇩🇪 · Sven Heinemeyer🇪🇸 · Wolfgang Hollik🇩🇪 · Georg Weiglein🇩🇪
Various methods are used in the literature for predicting the lightest CP-even Higgs boson mass in the Minimal Supersymmetric Standard Model (MSSM). Fixed-order diagrammatic calculations capture all effects at a given order and yield accurate results for scales of supersymmetric (SUSY) particles that are not separated too much from the weak scale. Effective field theory calculations allow a resummation of large logarithmic contributions up to all orders and therefore yield accurate results for a high SUSY scale. A hybrid approach, where both methods have been combined, is implemented in the computer code FeynHiggs. So far, however, at large scales sizeable differences have been observed between FeynHiggs and other pure EFT codes. In this work, the various approaches are analytically compared with each other in a simple scenario in which all SUSY mass scales are chosen to be equal to each other. Three main sources are identified that account for the major part of the observed differences. Firstly, it is shown that the scheme conversion of the input parameters that is commonly used for the comparison of fixed-order results is not adequate for the comparison of results containing a series of higher-order logarithms. Secondly, the treatment of higher-order terms arising from the determination of the Higgs propagator pole is addressed. Thirdly, the effect of different parametrizations in particular of the top Yukawa coupling in the non-logarithmic terms is investigated. Taking into account all of these effects, in the considered simple scenario very good agreement is found for scales above 1 TeV between the results obtained using the EFT approach and the hybrid approach of FeynHiggs.
hep-phEPJC(2018)·181 citations
08*
Muon Magnetic Moment and Lepton Flavor Violation in the Economical 3-3-1 Model
D. Cogollo🇧🇷
In this work we compute all relevant contributions stemming from the economical 3-3-1 model to the muon magnetic moment and the lepton flavor violation decay $μ \to e γ$ . Using the current bounds on these phenomena, we derive lower limits on the scale of symmetry breaking of the model. Moreover, taking into account existing limits from meson and collider studies we show that there is still room for a possible signal in $μ \to e γ$ in the near future.
hep-ph8 citations
09*
Renormalization-group evolution of new physics contributions to (semi)leptonic meson decays
Martín González-Alonso🇫🇷 · Jorge Martin Camalich🇨🇭 · Kin Mimouni🇨🇭
We study the renormalization group evolution (RGE) of new physics contributions to (semi)leptonic charged-current meson decays, focusing on operators involving a chirality flip at the quark level. We calculate their evolution under electroweak and electromagnetic interactions, including also the three-loop QCD running and provide numerical formulas that allow us to connect the values of the corresponding Wilson coefficients from scales at the TeV to the low-energy scales. The large mixing of the tensor operator into the (pseudo)scalar ones has important phenomenological implications, such as the RGE of new physics bounds obtained from light quark decays or in $b \to c ℓ ν$ transitions. For instance, we study scenarios involving tensor effective operators, which have been proposed in the literature to address the $B$ -decay anomalies, most notably those concerning the $R_{D^{(*)}}$ ratios. We conclude that the loop effects are important and should be taken into account in the analysis of these processes, especially if the operators are generated at an energy scale of $\sim 1$ TeV or higher.
hep-phPLB(2017)·175 citations
10*
Light Scalars and Dark Photons in Borexino and LSND Experiments
Maxim Pospelov🇨🇦 · Yu-Dai Tsai🇺🇸
Bringing an external radioactive source close to a large underground detector can significantly advance sensitivity not only to sterile neutrinos but also to "dark" gauge bosons and scalars. Here we address in detail the sensitivity reach of the Borexino-SOX configuration, which will see a powerful (a few PBq) $^{144}$ Ce $-^{144}$ Pr source installed next to the Borexino detector, to light scalar particles coupled to the SM fermions. The mass reach of this configuration is limited by the energy release in the radioactive $γ$ -cascade, which in this particular case is 2.2 MeV. Within that reach one year of operations will achieve an unprecedented sensitivity to coupling constants of such scalars, reaching down to $g \sim 1 0^{- 7}$ levels and probing significant parts of parameter space not excluded by either beam dump constraints or astrophysical bounds. Should the current proton charge radius discrepancy be caused by the exchange of a MeV-mass scalar, then the simplest models will be decisively probed in this setup. We also update the beam dump constraints on light scalars and vectors, and in particular rule out dark photons with masses below 1 MeV, and kinetic mixing couplings $ϵ ≳ 1 0^{- 5}$ .
hep-phhep-exPLB(2018)·47 citations
11*
Parton distributions from high-precision collider data
The NNPDF Collaboration: Richard D. Ball🇬🇧 · Valerio Bertone🇳🇱 · Stefano Carrazza🇨🇭 · Luigi Del Debbio🇬🇧 · Stefano Forte🇮🇹 · Patrick Groth-Merrild🇬🇧 · Alberto Guffanti🇮🇹 · Nathan P. Hartland🇳🇱 · Zahari Kassabov🇮🇹 · José I. Latorre🇪🇸 · Emanuele R. Nocera🇬🇧 · Juan Rojo🇳🇱 and 3 other authors
We present a new set of parton distributions, NNPDF3.1, which updates NNPDF3.0, the first global set of PDFs determined using a methodology validated by a closure test. The update is motivated by recent progress in methodology and available data, and involves both. On the methodological side, we now parametrize and determine the charm PDF alongside the light quarks and gluon ones, thereby increasing from seven to eight the number of independent PDFs. On the data side, we now include the D0 electron and muon W asymmetries from the final Tevatron dataset, the complete LHCb measurements of W and Z production in the forward region at 7 and 8 TeV, and new ATLAS and CMS measurements of inclusive jet and electroweak boson production. We also include for the first time top-quark pair differential distributions and the transverse momentum of the Z bosons from ATLAS and CMS. We investigate the impact of parametrizing charm and provide evidence that the accuracy and stability of the PDFs are thereby improved. We study the impact of the new data by producing a variety of determinations based on reduced datasets. We find that both improvements have a significant impact on the PDFs, with some substantial reductions in uncertainties, but with the new PDFs generally in agreement with the previous set at the one sigma level. The most significant changes are seen in the light-quark flavor separation, and in increased precision in the determination of the gluon. We explore the implications of NNPDF3.1 for LHC phenomenology at Run II, compare with recent LHC measurements at 13 TeV, provide updated predictions for Higgs production cross-sections and discuss the strangeness and charm content of the proton in light of our improved dataset and methodology. The NNPDF3.1 PDFs are delivered for the first time both as Hessian sets, and as optimized Monte Carlo sets with a compressed number of replicas.
hep-phhep-exEPJC(2017)·2518 citations
12*
On-Shell neutral Higgs bosons in the NMSSM with complex parameters
Florian Domingo🇪🇸 · Peter Drechsel🇩🇪 · Sebastian Paßehr🇩🇪
The Next-to-Minimal Supersymmetric Standard model (NMSSM) appears as an interesting candidate for the interpretation of the Higgs-measurement at the LHC and as a rich framework embedding physics beyond the Standard Model. We consider the renormalization of the Higgs sector of this model in its $C P$ -violating version, and propose a renormalization scheme for the calculation of on-shell Higgs masses. Moreover, the connection between the physical states and the tree-level ones is no longer trivial at the radiative level: a proper description of the corresponding transition thus proves necessary in order to calculate Higgs production and decays at a consistent loop order. After discussing these formal aspects, we compare the results of our mass calculation to the output of existing tools. We also study the relevance of the on-shell transition-matrix in the example of the $h_{i} \to τ^{+} τ^{-}$ width. We find deviations between our full prescription and popular approximations that can exceed $10%$ .
hep-phEPJC(2017)·24 citations
13*
Relaxed Inflation
Walter Tangarife🇮🇱 · Kohsaku Tobioka🇮🇱 · Lorenzo Ubaldi🇮🇱 · Tomer Volansky🇮🇱
We present an effective model where the inflaton is a relaxion that scans the Higgs mass and sets it at the weak scale. The dynamics consist of a long epoch in which inflation is due to the shallow slope of the potential, followed by a few number of e-folds where slow-roll is maintained thanks to dissipation via non-perturbative gauge-boson production. The same gauge bosons give rise to a strong electric field that triggers the production of electron-positron pairs via the Schwinger mechanism. The subsequent thermalization of these particles provides a novel mechanism of reheating. The relaxation of the Higgs mass occurs after reheating, when the inflaton/relaxion stops on a local minimum of the potential. We argue that this scenario may evade phenomenological and astrophysical bounds while allowing for the cutoff of the effective model to be close to the Planck scale. This framework provides an intriguing connection between inflation and the hierarchy problem.
hep-phastro-ph.CO23 citations
14*
Vacuum Topology and the Electroweak Phase Transition
Yiyang Zhang🇺🇸 · Francesc Ferrer🇺🇸 · Tanmay Vachaspati🇺🇸
We investigate if the topology of pure gauge fields in the electroweak vacuum can play a role in classical dynamics at the electroweak phase transition. Our numerical analysis shows that magnetic fields are produced if the initial vacuum has non-trivial Chern-Simons number, and the fields are helical if the Chern-Simons number changes during the phase transition.
↳ hep-thastro-ph.COhep-phPRD(2017)·9 citations
15*
Wilson lines in the MHV action
P. Kotko🇺🇸 · A. M. Stasto🇺🇸
The MHV action is the Yang-Mills action quantized on the light-front, where the two explicit physical gluonic degrees of freedom have been canonically transformed to a new set of fields. This transformation leads to the action with vertices being off-shell continuations of the MHV amplitudes. We show that the solution to the field transformation expressing one of the new fields in terms of the Yang-Mills field is a certain type of the Wilson line. More precisely, it is a straight infinite gauge link with a slope extending to the light-cone minus and the transverse direction. One of the consequences of that fact is that certain MHV vertices reduced partially on-shell are gauge invariant -- a fact discovered before using conventional light-front perturbation theory. We also analyze the diagrammatic content of the field transformations leading to the MHV action. We found that the diagrams for the solution to the transformation (given by the Wilson line) and its inverse differ only by light-front energy denominators. Further, we investigate the coordinate space version of the inverse solution to the one given by the Wilson line. We find an explicit expression given by a power series in fields. We also give a geometric interpretation to it by means of a specially defined vector field. Finally, we discuss the fact that the Wilson line solution to the transformation is directly related to the all-like helicity gluon wave function, while the inverse functional is a generating functional for solutions of self-dual Yang-Mills equations.
↳ hep-thhep-phJHEP(2017)·13 citations
16*
A complete non-perturbative renormalization prescription for quasi-PDFs
Constantia Alexandrou🇨🇾 · Krzysztof Cichy🇩🇪 · Martha Constantinou🇺🇸 · Kyriakos Hadjiyiannakou🇨🇾 · Karl Jansen🇩🇪 · Haralambos Panagopoulos🇨🇾 · Fernanda Steffens🇩🇪
In this work we present, for the first time, the non-perturbative renormalization for the unpolarized, helicity and transversity quasi-PDFs, in an RI' scheme. The proposed prescription addresses simultaneously all aspects of renormalization: logarithmic divergences, finite renormalization as well as the linear divergence which is present in the matrix elements of fermion operators with Wilson lines. Furthermore, for the case of the unpolarized quasi-PDFs, we describe how to eliminate the unwanted mixing with the twist-3 scalar operator. We utilize perturbation theory for the one-loop conversion factor that brings the renormalization functions to the MS-scheme at a scale of 2 GeV. We also explain how to improve the estimates on the renormalization functions by eliminating lattice artifacts. The latter can be computed in one-loop perturbation theory and to all orders in the lattice spacing. We apply the methodology for the renormalization to an ensemble of twisted mass fermions with Nf=2+1+1 dynamical light quarks, and a pion mass of around 375 MeV.
↳ hep-lathep-exhep-phhep-th+1NPB(2017)·212 citations
17*
Thermalized Axion Inflation
Ricardo Z. Ferreira🇪🇸 · Alessio Notari🇪🇸
We analyze the dynamics of inflationary models with a coupling of the inflaton $ϕ$ to gauge fields of the form $ϕF F ~ / f$ , as in the case of axions. It is known that this leads to an instability, with exponential amplification of gauge fields, controlled by the parameter $ξ = ϕ ˙ / (2 f H)$ , which can strongly affect the generation of cosmological perturbations and even the background. We show that scattering rates involving gauge fields can become larger than the expansion rate $H$ , due to the very large occupation numbers, and create a thermal bath of particles of temperature $T$ during inflation. In the thermal regime, energy is transferred to smaller scales, radically modifying the predictions of this scenario. We thus argue that previous constraints on $ξ$ are alleviated. If the gauge fields have Standard Model interactions, which naturally provides reheating, they thermalize already at $ξ ≳ 2.9$ , before perturbativity constraints and also before backreaction takes place. In absence of SM interactions (i.e. for a dark photon), we find that gauge fields and inflaton perturbations thermalize if $ξ ≳ 3.4$ ; however, observations require $ξ ≳ 6$ , which is above the perturbativity and backreaction bounds and so a dedicated study is required. After thermalization, though, the system should evolve non-trivially due to the competition between the instability and the gauge field thermal mass. If the thermal mass and the instabilities equilibrate, we expect an equilibrium temperature of $T_{e q} ≃ ξ H / g ˉ$ where $g ˉ$ is the effective gauge coupling. Finally, we estimate the spectrum of perturbations if $ϕ$ is thermal and find that the tensor to scalar ratio is suppressed by $H / (2 T)$ , if tensors do not thermalize.
↳ astro-ph.COgr-qchep-phhep-thJCAP(2017)·64 citations
18*
High-energy cosmic ray nuclei from tidal disruption events: Origin, survival, and implications
B. Theodore Zhang🇨🇳 · Kohta Murase🇺🇸 · Foteini Oikonomou🇺🇸 · Zhuo Li🇨🇳
Tidal disruption events (TDEs) by supermassive or intermediate mass black holes have been suggested as candidate sources of ultrahigh-energy cosmic rays (UHECRs) and high-energy neutrinos. Motivated by the recent measurements from the Pierre Auger Observatory, which indicates a metal-rich cosmic-ray composition at ultrahigh energies, we investigate the fate of UHECR nuclei loaded in TDE jets. First, we consider the production and survival of UHECR nuclei at internal shocks, external forward and reverse shocks, and nonrelativistic winds. Based on the observations of Swift J1644+57, we show that the UHECRs can survive for external reverse and forward shocks, and disk winds. On the other hand, UHECR nuclei are significantly disintegrated in internal shocks, although they could survive for low-luminosity TDE jets. Assuming that UHECR nuclei can survive, we consider implications of different composition models of TDEs. We find that the tidal disruption of main sequence stars or carbon-oxygen white dwarfs does not successfully reproduce UHECR observations, namely the observed composition or spectrum. The observed mean depth of the shower maximum and its deviation could be explained by oxygen-neon-magnesium white dwarfs, but they may be too rare to be the sources of UHECRs.
↳ astro-ph.HEastro-ph.SRhep-phnucl-thPRD(2017)·80 citations

* Reconstructed cohort: no mailing for this day survives in the archive. Papers are grouped by their submission times and arXiv's announcement cut-off, assuming announcement without delay; positions follow identifier order. Validated at ~91% exact-day agreement against the archived era.