HEP Phenomenology·hep-ph
24 papers—20 primary·4 cross-listed·reconstructed*
I present approximate next-to-next-to-leading-order (aNNLO) transverse-momentum () distributions in single-top production processes. The aNNLO results are derived from next-to-next-to-leading-logarithm (NNLL) resummation of soft-gluon corrections in the differential cross section. Single-top as well as single-antitop distributions are shown in -channel, -channel, and production for LHC energies.
James Barnard🇦🇺 · Peter Cox🇦🇺 · Tony Gherghetta🇺🇸 · Andrew Spray🇦🇺
Long-lived, colour-triplet scalars are a generic prediction of unnatural, or split, composite Higgs models where the spontaneous global-symmetry breaking scale TeV and an unbroken symmetry is preserved. Since the triplet scalars are pseudo Nambu-Goldstone bosons they are split from the much heavier composite-sector resonances and are the lightest exotic, coloured states. This makes them ideal to search for at colliders. Due to discrete symmetries the triplet scalar decays via a dimension-six term and given the large suppression scale is often metastable. We show that existing searches for collider-stable R-hadrons from Run-I at the LHC forbid a triplet scalar mass below 845 GeV, whereas with at 13 TeV triplet scalar masses up to 1.4 TeV can be discovered. For shorter lifetimes displaced-vertex searches provide a discovery reach of up to 1.8 TeV. In addition we present exclusion and discovery reaches of future hadron colliders as well as indirect limits that arise from modifications of the Higgs couplings.
The absence of low energy supersymmetry in run I data at the LHC has pushed the nominal scale for supersymmetry beyond a TeV. While this is consistent with the discovery of the Higgs boson at \approx 125 GeV, simple models with scalar and gaugino mass universality are being pushed into corners of parameter space. Some possibilities within the constrained minimal supersymmetric extension of the standard model (with four parameters) are discussed along with a one parameter extension in which the Higgs soft masses are non-universal. Also discussed are 2-, 3-, and 4-parameter versions of pure gravity mediated models with a wino, Higgsino, or bino LSP respectively.
Recently we proposed a model for light Dirac neutrinos in which two right-handed (RH) neutrinos per generation are added to the particles of the Standard Model (SM), implemented with the symmetry of fermionic contents. The ordinary one is decoupled via the high scale type-I seesaw mechanism, while the extra pairs off with its left-handed (LH) partner. The symmetry of lepton and quark contents was merely used as a guideline to the choice of parameters because it is not a proper symmetry. Here we argue that the underlying symmetry to take for this correspondence is presymmetry, the hidden electroweak symmetry of the SM extended with RH neutrinos defined by transformations which exchange lepton and quark bare states with the same electroweak charges and no Majorana mass terms in the underlying Lagrangian. It gives a topological character to fractional charges, relates the number of families to the number of quark colors, and now guarantees the great disparity between the couplings of the two RH neutrinos. Thus, Dirac neutrinos with extremely small masses appear as natural predictions of presymmetry, satisfying the 't Hooft's naturalness conditions in the extended seesaw where the extra RH neutrinos serve to adulterate the mass properties in the low scale effective theory, which retains without extensions the gauge and Higgs sectors of the SM. However, the high energy threshold for the seesaw implies new physics to stabilize the quantum corrections to the Higgs boson mass in agreement with the naturalness requirement.
Kevork N. Abazajian🇺🇸 · Ryan E. Keeley (UC Irvine)🇺🇸
We incorporate Milky Way dark matter halo profile uncertainties, as well as an accounting of diffuse gamma-ray emission uncertainties in dark matter annihilation models for the Galactic Center Extended gamma-ray excess (GCE) detected by the Fermi Gamma Ray Space Telescope. The range of particle annihilation rate and masses expand when including these unknowns. However, two of the most precise empirical determinations of the Milky Way halo's local density and density profile leave the signal region to be in considerable tension with dark matter annihilation searches from combined dwarf galaxy analyses for single-channel dark matter annihilation models. The GCE and dwarf tension can be alleviated if: one, the halo is very highly concentrated or strongly contracted; two, the dark matter annihilation signal differentiates between dwarfs and the GC; or, three, local stellar density measures are found to be significantly lower, like that from recent stellar counts, increasing the local dark matter density.
I discuss how the rapidity evolution of gluon transverse momentum dependent distribution changes from nonlinear evolution at small to linear evolution at moderate .
W. Abdallah🇪🇬 · J. Fiaschi🇬🇧 · S. Khalil🇪🇬 · S. Moretti🇬🇧
Search for invisible final states produced at the Large Hadron Collider (LHC) by new physics scenarios are normally carried out resorting to a variety of probes emerging from the initial state, in the form of single-jet, -photon and - boson signatures. These are particularly effective for models of Supersymmetry (SUSY) in presence of -parity conservation, owing to the presence in their spectra of a stable neutralino as dark matter candidate. We assume here as theoretical framework Supersymmetric () extension of the Standard Model (BLSSM), wherein a mediator for invisible decays can be boson. The peculiarity of the signal is thus that the final state objects carry a very large (transverse) missing energy, since the is naturally massive and constrained by direct searches and electro-weak precision tests to be at least in TeV scale region. Under these circumstances the efficiency in accessing the invisible final state and rejecting the standard model background is very high. This somehow compensates the rather meagre production rates. Another special feature of this invisible BLSSM signal is its composition, which is often dominated by sneutrino decays (alongside the more traditional neutrino and neutralino modes). Sensitivity of the CERN machine to these two features can therefore help disentangling the BLSSM from more popular SUSY models. We assess in this analysis the scope of the LHC in establishing the aforementioned invisible signals through a sophisticated signal-to-background simulation carried out in presence of parton shower, hadronisation and detector effects. We find that significant sensitivity exists already after 300 fb during Run 2. We find that mono-jet events can be readily accessible at the LHC, so as to enable one to claim a prompt discovery, while mono-photon and - signals can be used as diagnostic tools of the underlying scenario.
A.B. Arbuzov🇷🇺 · T.V. Kopylova🇷🇺
QED radiative corrections to elastic electron-proton scattering at low energies are discussed. Corrections to the electron line and effects due to vacuum polarization are computed. Higher order effects are estimated for the conditions of the experiment on the electric and magnetic proton form factors by A1 Collaboration. Calculations are performed within the next-to-leading approximation. Inclusion of the higher order effects can affect the value of the proton charge radius extracted from the experimental data.
Masaki Yamada🇯🇵 · Tsutomu T. Yanagida🇯🇵 · Kazuya Yonekura🇯🇵
Although QCD axion models are widely studied as solutions to the strong CP problem, they generically confront severe fine-tuning problems to guarantee the anomalous PQ symmetry. In this letter, we propose a simple QCD axion model without any fine-tunings. We introduce an extra dimension and a pair of extra quarks living on two branes separately, which is also charged under a bulk Abelian gauge symmetry. We assume a monopole condensation on our brane at an intermediate scale, which implies that the extra quarks develop the chiral symmetry breaking and the PQ symmetry is broken. In contrast to the original Kim's model, our model explains the origin of the PQ symmetry thanks to the extra dimension and avoids the cosmological domain wall problem because of the chiral symmetry breaking in the Abelian gauge theory.
Shuichiro Funatsu🇯🇵 · Hisaki Hatanaka🇰🇷 · Yutaka Hosotani🇯🇵
The decay rate of the Higgs decay is evaluated at the one-loop level in the gauge-Higgs unification. Although an infinite number of loops with Kaluza-Klein states contribute to the decay amplitude, there appears the cancellation among the loops, and the decay rate is found to be finite and non-zero. It is found that the decay rate is well approximated by the decay rate in the standard model multiplied by , where is the Aharonov-Bohm phase induced by the vacuum expectation value of an extra-dimensional component of the gauge field.
Pablo Sanchez-Puertas🇩🇪 · Pere Masjuan🇩🇪
The pseudoscalar decays into lepton pairs are analyzed with the machinery of Canterbury approximants, an extension of Padé approximants to bivariate functions. This framework provides an ideal model-independent approach to implement all our knowledge of the pseudoscalar transition form factors driving these decays, can be used for data analysis, and allows to include experimental data and theoretical constraints in an easy way, and determine a systematic error. We find that previous theoretical estimates for these branching ratios have underestimated their theoretical uncertainties. From our updated results, the existing experimental discrepancies for and channels cannot be explained unless the doubly-virtual transition form factors behavior -not yet measured- are out of theoretical expectations, which is an interesting result both for anomalous magnetic moments of leptons, and for physics beyond the standard model.
M. Bayar🇹🇷 · P. Fernandez-Soler🇪🇸 · Zhi-Feng Sun🇪🇸 · E. Oset🇪🇸
In this work we study the three-body system solving the Faddeev equations in the fixed center approximation. We assume the system forming a cluster, and in terms of the two-body unitarized scattering amplitudes in the local Hidden Gauge approach we find a new state. The mass of the new state corresponds to a two particle invariant mass of the system close to the resonant energy of the , indicating that the role of this resonance is important in the dynamical generation of the new state.
A new family of inflation models is introduced and studied. The models are characterised by a scalar potential which, far from the origin, approaches an inflationary plateau in a power-law manner, while near the origin becomes monomial, as in chaotic inflation. The models are obtained in the context of global supersymmetry starting with a superpotential, which interpolates from a generalised monomial to an O'Raifearteagh form for small to large values of the inflaton field respectively. It is demonstrated that the observables obtained, such as the scalar spectral index, its running and the tensor to scalar ratio, are in excellent agreement with the latest observations, without any fine-tuning. Moreover, by widening mildly the shaft in field space, it is shown that sizable tensors can be generated, which may well be observable in the near future.
M. Albaladejo🇪🇸 · B. Moussallam
A reliable determination of the isospin breaking double quark mass ratio from precise experimental data on decays should be based on the chiral expansion of the amplitude supplemented with a Khuri-Treiman type dispersive treatment of the final-state interactions. We discuss an extension of this formalism which allows to estimate the effects of the and resonances and their mixing on the amplitudes. Matrix generalisations of the equations describing elastic rescattering with are introduced which accomodate both and coupled-channel rescattering. Isospin violation induced by the physical mass difference and by direct mass difference effects are both accounted for in the dispersive integrals. Numerical solutions are constructed which illustrate how the large resonance effects at 1 GeV propagate down to low energies. They remain small in the physical region of the decay, due to the matching constraints with the NLO chiral amplitude, but they are not negligible and go in the sense of further improving the agreement with experiment for the Dalitz plot parameters.
The recent LHCb discovery of states , , believed to be pentaquark resonances, begs the question of whether equivalent states with exist, and how they might be produced. The precise analogue to the discovery channel , namely, , is feasible for this study and indeed is less Cabibbo-suppressed, although its limited phase space suggests that evidence of a resonance would be confined to the kinematic endpoint region.
After motivation and short presentation of the minimal supersymmetric model with R-symmetry (MRSSM), we address the question of accomodating the measured Higgs boson mass in accordance with electroweak precision observables and LHC constraints.
Lukas Graf🇬🇧 · Julia Harz🇬🇧 · Wei-Chih Huang🇬🇧
The constraints on baryogenesis models obtained from an observation of neutrinoless double beta decay are discussed. The lepton number violating processes, which can underlie neutrinoless double beta decay, would together with sphaleron processes, which are effective in a wide range of energies, wash out any primordial baryon asymmetry of the universe. Typically, if a mechanism of neutrinoless double beta decay other than the standard light neutrino exchange is observed, typical scenarios of high-scale baryogenesis will be excluded. This can be achieved by different methods, e.g. through the observation in multiple isotopes or the measurement of the decay distribution. In addition, we will also highlight the connection with low energy lepton flavour violation and lepton number violation at the LHC.
A. Abada🇫🇷 · V. De Romeri🇫🇷 · A.M. Teixeira🇫🇷
We discuss charged lepton flavour violating processes occurring in the presence of muonic atoms, such as muon-electron conversion in nuclei , the (Coulomb enhanced) decay of muonic atoms into a pair of electrons BR(, N), as well as Muonium conversion and decay, and . Any experimental signal of these observables calls for scenarios of physics beyond the Standard Model. In this work, we consider minimal extensions of the Standard Model via the addition of sterile fermions, providing the corresponding complete analytical expressions for all the considered observables. We first consider an "ad hoc" extension with a single sterile fermion state, and investigate its impact on the above observables. Two well motivated mechanisms of neutrino mass generation are then considered: the Inverse Seesaw embedded into the Standard Model, and the MSM. Our study reveals that, depending on their mass range and on the active-sterile mixing angles, sterile neutrinos can give significant contributions to the above mentioned observables, some of them even lying within present and future sensitivity of dedicated cLFV experiments. We complete the analysis by confronting our results to other (direct and indirect) searches for sterile fermions.
Ryuji Daido🇯🇵 · Naoya Kitajima🇯🇵 · Fuminobu Takahashi🇯🇵
We study a level crossing between the QCD axion and an axion-like particle, focusing on the recently found phenomenon, the axion roulette, where the axion-like particle runs along the potential, passing through many crests and troughs, until it gets trapped in one of the potential minima. We perform detailed numerical calculations to determine the parameter space where the axion roulette takes place, and as a result domain walls are likely formed. The domain wall network without cosmic strings is practically stable, and it is nothing but a cosmological disaster. In a certain case, one can make domain walls unstable and decay quickly by introducing an energy bias without spoiling the Peccei-Quinn solution to the strong CP problem.
Vittorio Del Duca🇮🇹 · Eric Laenen🇳🇱
We review the present situation in top quark physics, in these early days of Run II of the LHC. We take mostly a Standard Model perspective, showing recent results, and review the key concepts and results of the associated theoretical predictions. The issues we discuss are the top quark mass, top quark pair and single top production, production in association with other particles, charge asymmetry and top quark decay.
Ahmed Farag Ali🇺🇸 · Mohammed M. Khalil🇪🇬 · Elias C. Vagenas🇰🇼
The existence of a minimal length is a common prediction of various theories of quantum gravity. This minimal length leads to a modification of the Heisenberg uncertainty principle to a Generalized Uncertainty Principle (GUP). Various studies showed that a GUP modifies the Hawking radiation of black holes. In this paper, we propose a modification of the Schwarzschild metric based on the modified Hawking temperature derived from the GUP. Based on this modified metric, we calculate corrections to the deflection of light, time delay of light, perihelion precession, and gravitational redshift. We compare our results with gravitational measurements to set an upper bound on the GUP parameter.
J. F. de Medeiros Neto🇧🇷 · Rudnei O. Ramos🇧🇷 · Carlos Rafael M. Santos🇧🇷 · Rodrigo F. Ozela🇧🇷 · Gabriel C. Magalhães🇧🇷 · Van Sérgio Alves🇧🇷
The Casimir force for a planar gauge model is studied considering perfect conducting and perfect magnetically permeable boundaries. By using an effective model describing planar vortex excitations, we determine the effect these can have on the Casimir force between parallel lines. Two different mappings between models are considered for the system under study, where generic boundary conditions can be more easily applied and the Casimir force be derived in a more straightforward way. It is shown that vortex excitations can be an efficient suppressor of vacuum fluctuations. In particular, for the model studied here, a planar Chern-Simons type of model that allows for the presence of vortex matter, the Casimir force is found to be independent of the choice of boundary conditions, at least for the more common types, like Neumann, perfect conducting and magnetically permeable boundary conditions. We give an interpretation for these results and some possible applications for them are also discussed.
JLQCD Collaboration: S. Aoki🇯🇵 · G. Cossu🇯🇵 · X. Feng🇺🇸 · S. Hashimoto🇯🇵 · T. Kaneko🇯🇵 · J. Noaki🇯🇵 · T. Onogi🇯🇵
We study the chiral behavior of the electromagnetic (EM) form factors of pion and kaon in three-flavor lattice QCD. In order to make a direct comparison of the lattice data with chiral perturbation theory (ChPT), we employ the overlap quark action that has exact chiral symmetry. Gauge ensembles are generated at a lattice spacing of 0.11 fm with four pion masses ranging between M_pi \simeq 290 MeV and 540 MeV and with a strange quark mass m_s close to its physical value. We utilize the all-to-all quark propagator technique to calculate the EM form factors with high precision. Their dependence on m_s and on the momentum transfer is studied by using the reweighting technique and the twisted boundary conditions for the quark fields, respectively. A detailed comparison with SU(2) and SU(3) ChPT reveals that the next-to-next-to-leading order terms in the chiral expansion are important to describe the chiral behavior of the form factors in the pion mass range studied in this work. We estimate the relevant low-energy constants and the charge radii, and find reasonable agreement with phenomenological and experimental results.
Jean-Paul Blaizot🇫🇷 · Yoshimasa Hidaka🇯🇵 · Daisuke Satow🇮🇹
We evaluate the spectral properties of the Goldstino in a Bose-Fermi mixture of cold atoms and molecules whose dynamics is governed by a supersymmetric hamiltonian. Model independent results are obtained from sum rules obeyed by the spectral function. We carry out specific calculations, at zero and finite temperature, using the Random Phase Approximation, and obtain in particular analytic expressions for the dispersion relation at small momentum. These explicit calculations allow us to pin down more precisely the features of the Goldstino that can be attributed to the supersymmetry alone, together with its spontaneous breaking. The anomalous large effect of the Fermi sea at moderate and large momenta is emphasized.
* 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.