Wed·Jan 17, 2018Wednesday·January 17, 2018

1. 01*

   Neutrino masses and their ordering: Global Data, Priors and Models

   S. Gariazzo🇪🇸 · M. Archidiacono🇩🇪 · P.F. de Salas🇪🇸 · O. Mena🇪🇸 · C.A. Ternes🇪🇸 · M. Tórtola🇪🇸

   We present a Bayesian analysis of the combination of current neutrino oscillation, neutrinoless double beta decay and CMB observations. Our major goal is to carefully investigate the possibility to single out one neutrino mass ordering, Normal Ordering or Inverted Ordering, with current data. Two possible parametrizations (three neutrino masses versus the lightest neutrino mass plus the two oscillation mass splittings) and priors (linear versus logarithmic) are examined. We find that the preference for NO is only driven by neutrino oscillation data. Moreover, the values of the Bayes factor indicate that the evidence for NO is strong only when the scan is performed over the three neutrino masses with logarithmic priors; for every other combination of parameterization and prior, the preference for NO is only weak. As a by-product of our Bayesian analyses, we are able to a) compare the Bayesian bounds on the neutrino mixing parameters to those obtained by means of frequentist approaches, finding a very good agreement; b) determine that the lightest neutrino mass plus the two mass splittings parametrization, motivated by the physical observables, is strongly preferred over the three neutrino mass eigenstates scan and c) find that there is a weak-to-moderate preference for logarithmic priors. These results establish the optimal strategy to successfully explore the neutrino parameter space, based on the use of the oscillation mass splittings and a logarithmic prior on the lightest neutrino mass. We also show that the limits on the total neutrino mass $\sum m_{\nu }$ can change dramatically when moving from one prior to the other. These results have profound implications for future studies on the neutrino mass ordering, as they crucially state the need for self-consistent analyses which explore the best parametrization and priors, without combining results that involve different assumptions.

   hep-phastro-ph.COJCAP(2018)·141 citations
2. 02*

   Probing the CP nature of the Higgs coupling in $t\bar{t}h$ events at the LHC

   E. Gouveia🇵🇹 · S. P. Amor dos Santos🇵🇹 · M. C. N. Fiolhais🇵🇹 · R. Frederix🇩🇪 · R. Gonçalo🇵🇹 · R. Martins🇵🇹 · A. Onofre🇵🇹 · C. M. Pease🇵🇹 · H. Peixoto🇵🇹 · A. Reigoto🇵🇹 · R. Santos🇵🇹 · J. Silva🇵🇹

   The determination of the CP nature of the top quark Yukawa coupling is addressed in this phenomenological work, using $t\bar{t}h$ events at the $\sqrt{s}$ = 13 TeV LHC, with $h\to b\bar{b}$ and through the dilepton decay channel of $t\bar{t}$. Signal events were generated for pure $CP$-even, pure $CP$-odd and mixed-$CP$ coupling scenarios. Standard Model (SM) backgrounds were also considered. Angular distributions and asymmetries were studied and found to be potentially good probes to the $CP$ nature of the coupling, even after detector simulation and full event reconstruction using a kinematic fit. Expected limits to the $t\bar{t}h$ production cross-section times branching ratio were obtained for a range of top quark Yukawa $CP$-mixing angles and for different integrated luminosities of the LHC.

   hep-ph2 citations
3. 03*

   New SUSY Fits for the ILC and CLIC

   S. Heinemeyer🇪🇸

   We review the MasterCode fits of several incarnations of the Minimal Supersymmetric Standard Model (MSSM). These include the GUT models based on mAMSB and SU(5), sub-GUT models as well as a model defined at low energies with 11 free parameters, the pMSSM11. The fit combines consistently measurements of Higgs boson properties, searches for additional Higgs bosons and supersymmetric (SUSY) particles, low-energy and flavor experiments as well as Dark Matter (DM) measurements. We predict the preferred SUSY mass spectra in these models and analyze the discovery potential of future e+e- colliders such as the ILC and CLIC.

   hep-ph3 citations
4. 04*

   Production of Electroweak SUSY Particles at ILC and CLIC

   S. Heinemeyer🇪🇸 · C. Schappacher🇩🇪

   For the search for electroweak particles in the Minimal Supersymmetric Standard Model (MSSM) as well as for future precision analyses of these particles an accurate knowledge of their production and decay properties is mandatory. We review the evaluation of the cross sections for the chargino, neutralino and scalar lepton production at e+e- colliders in the MSSM with complex parameters (cMSSM). The evaluation is based on a full one-loop calculation of the various production mechanisms, including soft and hard photon radiation. The dependence of the chargino/neutralino/slepton cross sections on the relevant cMSSM parameters is analyzed numerically. We find sizable contributions to many production cross sections. They amount roughly +- 15% of the tree-level results, but can go up to +-40% or higher in extreme cases. Also the complex phase dependence of the one-loop corrections was found non-negligible. The full one-loop contributions are thus crucial for physics analyses at a future linear e+e- collider such as the ILC or CLIC.

   hep-ph1 citation
5. 05*

   Probing underlying event in Z-boson events using event shape observables

   Deepak Kar🇿🇦 · Dimbiniaina Soanasolo Rafanoharana🇿🇦

   Experimental measurements of observables sensitive to the underlying event (UE) in $Z$-boson events have been performed by both ATLAS and CMS experiments at the LHC. However, in the busy LHC environment, these observables receive substantial contribution from jets originating from initial state radiation (ISR). We probe if using event shape observables in conjunction with the UE observables can help us to disentangle the effect of the UE from jets originating in ISR.

   hep-phInt.J.Mod.Phys.A(2019)·3 citations
6. 06*

   Single-scale Renormalisation Group Improvement of Multi-scale Effective Potentials

   Leonardo Chataignier🇩🇪 · Tomislav Prokopec🇳🇱 · Michael G. Schmidt🇩🇪 · Bogumila Swiezewska🇳🇱

   We present a new method for renormalisation group improvement of the effective potential of a quantum field theory with an arbitrary number of scalar fields. The method amounts to solving the renormalisation group equation for the effective potential with the boundary conditions chosen on the hypersurface where quantum corrections vanish. This hypersurface is defined through a suitable choice of a field-dependent value for the renormalisation scale. The method can be applied to any order in perturbation theory and it is a generalisation of the standard procedure valid for the one-field case. In our method, however, the choice of the renormalisation scale does not eliminate individual logarithmic terms but rather the entire loop corrections to the effective potential. It allows us to evaluate the improved effective potential for arbitrary values of the scalar fields using the tree-level potential with running coupling constants as long as they remain perturbative. This opens the possibility of studying various applications which require an analysis of multi-field effective potentials across different energy scales. In particular, the issue of stability of the scalar potential can be easily studied beyond tree level.

   hep-phhep-thJHEP(2018)·42 citations
7. 07*

   Effective theory analysis for vector-like quark model

   Takuya Morozumi🇯🇵 · Yusuke Shimizu🇯🇵 · Shunya Takahashi🇯🇵 · Hiroyuki Umeeda🇯🇵

   We study a model with a down-type SU(2) singlet vector-like quark (VLQ) as a minimal extension of the standard model (SM). In this model, flavor changing neutral currents (FCNCs) arise at tree level and the unitarity of the $3\times 3$ Cabibbo-Kobayashi-Maskawa (CKM) matrix does not hold. In this paper, we constrain the FCNC coupling from $b\to s$ transitions, especially $B_s\to {\mu }^{+}{\mu }^{-}$ and $\bar{B}\to X_s\gamma$ processes. In order to analyze these processes, we derive an effective Lagrangian which is valid below the electroweak symmetry breaking scale. For this purpose, we first integrate out the VLQ field and derive an effective theory by matching Wilson coefficients up to one-loop level. Using the effective theory, we construct the effective Lagrangian for $b\to s{\gamma }^{(\ast )}$. It includes the effects of the SM quarks and the violation of the CKM unitarity. We show the constraints on the magnitude of the FCNC coupling and its phase by taking account of the current experimental data on $\Delta M_{B_s}$, $\mathrm{Br}[B_s\to {\mu }^{+}{\mu }^{-}]$, $\mathrm{Br}[\bar{B}\to X_s\gamma ]$ and CKM matrix elements as well as theoretical uncertainties. We find that the constraint from the $\mathrm{Br}[B_s\to {\mu }^{+}{\mu }^{-}]$ is more stringent than that from the $\mathrm{Br}[\bar{B}\to X_s\gamma$]. We also obtain the bound for the mass of the VLQ and the strength of the Yukawa couplings related to the FCNC coupling of $b\to s$ transition. Using the CKM elements which satisfy above constraints, we show how the unitarity is violated on the complex plane.

   hep-phhep-exPTEP(2018)·9 citations
8. 08*

   Ameliorating the Higgs mass fine-tuning problem with multi-Higgs doublet models

   Nabarun Chakrabarty🇮🇳 · Indrani Chakraborty🇮🇳

   With no conclusive signal till date of the minimal supersymmetric and extra dimensional models at the Large Hadron Collider (LHC), the issue of fine-tuning of the Higgs mass still calls for some attention. It could be very possible that the observed Higgs boson of mass 125 GeV has its origin in a non-supersymmetric extended scalar sector, and, it still has properties strikingly similar to the Standard Model Higgs. In such cases, however, one relies upon possible cancellations in the quadratic divergence of the Higgs mass to uphold naturalness. In this work, we have investigated this possibility in context of some two Higgs doublet and three Higgs doublet scenarios.

   hep-phInt.J.Mod.Phys.A(2019)·12 citations
9. 09*

   $\mathcal{C}\mathcal{P}$-violating effects on MSSM Higgs searches

   Shruti Patel🇩🇪 · Elina Fuchs🇮🇱 · Stefan Liebler🇩🇪 · Georg Weiglein🇩🇪

   We study the effects of $\mathcal{C}\mathcal{P}$-violating phases on the phenomenology of the Higgs sector of the MSSM. Complex parameters in the MSSM lead to $\mathcal{C}\mathcal{P}$-violating mixing between the tree-level $\mathcal{C}\mathcal{P}$-even and $\mathcal{C}\mathcal{P}$-odd neutral Higgs states, leading to three new loop-corrected mass eigenstates $h_a$, $a\in \{1,2,3\}$. For scenarios where a light Higgs boson at about 125 GeV can be identified with the observed signal and where the other Higgs states are significantly heavier, a large admixture of the heavy neutral Higgs bosons occurs as a generic feature if $\mathcal{C}\mathcal{P}$-violating effects are taken into account. Including interference contributions in the predictions for cross sections times branching ratios of the Higgs bosons is essential in this case. As a first step, we present the gluon-fusion and bottom-quark annihilation cross sections for $h_a$ for the general case of arbitrary complex parameters, and we demonstrate that squark effects strongly depend on the phases of the complex parameters. We then study the effects of interference between $h_2$ and $h_3$ for the example of the process $b\bar{b}\to {\tau }^{+}{\tau }^{-}$. We show that large destructive interference effects modify LHC exclusion bounds such that parts of the parameter space that would be excluded by MSSM Higgs searches under the assumption of $\mathcal{C}\mathcal{P}$-conservation open up when the possibility of $\mathcal{C}\mathcal{P}$-violation in the Higgs sector is accounted for.

   hep-phActa Phys.Polon.Supp.(2018)·2 citations
10. 10*

    Hall effect in the presence of rotation

    M.A.Zubkov🇮🇱

    The rotating relativistic fermion system is considered. The consideration is based on the Dirac equation written in the laboratory (non - rotating) reference frame. Rotation in this approach gives rise to the effective magnetic and electric fields that act in the same way both on positive and negative electric charges. In the presence of external electric field in the given system the electric current appears orthogonal to both the electric field and the axis of rotation. The possible applications to the physics of quark - gluon plasma are discussed.

    hep-phEPL(2018)·15 citations
11. 11*

    Vacuum Polarization and Photon Propagation in an Electromagnetic Plane Wave

    Akihiro Yatabe🇯🇵 · Shoichi Yamada🇯🇵

    The QED vacuum polarization in external monochromatic plane-wave electromagnetic fields is calculated with spatial and temporal variations of the external fields being taken into account. We develop a perturbation theory to calculate the induced electromagnetic current that appears in the Maxwell equations, based on Schwinger's proper-time method, and combine it with the so-called gradient expansion to handle the variation of external fields perturbatively. The crossed field, i.e., the long wavelength limit of the electromagnetic wave is first considered. The eigenmodes and the refractive indices as the eigenvalues associated with the eigenmodes are computed numerically for the probe photon propagating in some particular directions. In so doing, no limitation is imposed on the field strength and the photon energy unlike previous studies. It is shown that the real part of the refractive index becomes less than unity for strong fields, the phenomenon that has been known to occur for high-energy probe photons. We then evaluate numerically the lowest-order corrections to the crossed-field resulting from the field variations in space and time. It is demonstrated that the corrections occur mainly in the imaginary part of the refractive index.

    hep-phastro-ph.HEPTEP(2018)·2 citations
12. 12*

    Charged Fermions Below 100 GeV

    Daniel Egana-Ugrinovic🇺🇸 · Matthew Low🇺🇸 · Joshua T. Ruderman🇺🇸

    How light can a fermion be if it has unit electric charge? We revisit the lore that LEP robustly excludes charged fermions lighter than about 100 GeV. We review LEP chargino searches, and find them to exclude charged fermions lighter than 90 GeV, assuming a higgsino-like cross section. However, if the charged fermion couples to a new scalar, destructive interference among production channels can lower the LEP cross section by a factor of 3. In this case, we find that charged fermions as light as 75 GeV can evade LEP bounds, while remaining consistent with constraints from the LHC. As the LHC collects more data, charged fermions in the 75-100 GeV mass range serve as a target for future monojet and disappearing track searches.

    hep-phhep-exJHEP(2018)·51 citations
13. 13*

    Classification of NLO operators for composite Higgs models

    T.Alanne🇩🇪 · N.Bizot🇫🇷 · G.Cacciapaglia🇫🇷 · F.Sannino🇩🇰

    We provide a general classification of template operators, up to next-to-leading order, that appear in chiral perturbation theories based on the two flavour patterns of spontaneous symmetry breaking SU($N_F$)/Sp($N_F$) and SU($N_F$)/SO($N_F$). All possible explicit-breaking sources parametrised by spurions transforming in the fundamental and in the two-index representations of the flavour symmetry are included. While our general framework can be applied to any model of strong dynamics, we specialise to composite-Higgs models, where the main explicit breaking sources are a current mass, the gauging of flavour symmetries, and the Yukawa couplings (for the top). For the top, we consider both bilinear couplings and linear ones a la partial compositeness. Our templates provide a basis for lattice calculations in specific models. As a special example, we consider the SU(4)/Sp(4)$\cong$ SO(6)/SO(5) pattern which corresponds to the minimal fundamental composite-Higgs model. We further revisit issues related to the misalignment of the vacuum. In particular, we shed light on the physical properties of the singlet $\eta$, showing that it cannot develop a vacuum expectation value without explicit CP violation in the underlying theory.

    hep-phPRD(2018)·41 citations
14. 14*

    Initial conditions for Inflation in an FRW Universe

    Swagat S. Mishra🇮🇳 · Varun Sahni🇮🇳 · Alexey V. Toporensky🇷🇺

    We examine the class of initial conditions which give rise to inflation. Our analysis is carried out for several popular models including: Higgs inflation, Starobinsky inflation, chaotic inflation, axion monodromy inflation and non-canonical inflation. In each case we determine the set of initial conditions which give rise to sufficient inflation, with at least $60$ e-foldings. A phase-space analysis has been performed for each of these models and the effect of the initial inflationary energy scale on inflation has been studied numerically. This paper discusses two scenarios of Higgs inflation: (i) the Higgs is coupled to the scalar curvature, (ii) the Higgs Lagrangian contains a non-canonical kinetic term. In both cases we find Higgs inflation to be very robust since it can arise for a large class of initial conditions. One of the central results of our analysis is that, for plateau-like potentials associated with the Higgs and Starobinsky models, inflation can be realised even for initial scalar field values which lie close to the minimum of the potential. This dispels a misconception relating to plateau potentials prevailing in the literature. We also find that inflation in all models is more robust for larger values of the initial energy scale.

    ↳ gr-qcastro-ph.COhep-phhep-thPRD(2018)·58 citations
15. 15*

    Top Quark Modeling and Generators in CMS

    Efe Yazgan (for the CMS Collaboration)🇨🇳

    Recent top quark event modeling studies done using LHC proton-proton collision data collected with the CMS detector at centre of mass energies of 8 and 13 TeV and state-of-the-art theoretical predictions are summarized. A new factorized approach for parton shower uncertainties is presented. A top quark specific PYTHIA8 CMS tune, along with tunes using new color reconnection models, is discussed. The possibility of having a consistent choice of parton distribution function in the matrix element and the parton shower is demonstrated with tunes constructed with leading, next-to-leading, and next-to-next-to-leading order versions of NNPDF3.1 set compared to minimum bias and underlying event data.

    ↳ hep-exhep-ph1 citation
16. 16*

    Physics with Reactor Neutrinos

    Xin Qian🇺🇸 · Jen-Chieh Peng🇺🇸

    Neutrinos produced by nuclear reactors have played a major role in advancing our knowledge of the properties of neutrinos. The first direct detection of the neutrino, confirming its existence, was performed using reactor neutrinos. More recent experiments utilizing reactor neutrinos have also found clear evidence for neutrino oscillation, providing unique input for the determination of neutrino mass and mixing. Ongoing and future reactor neutrino experiments will explore other important issues, including the neutrino mass hierarchy and the search for sterile neutrinos and other new physics beyond the standard model. In this article, we review the recent progress in physics using reactor neutrinos and the opportunities they offer for future discoveries.

    ↳ hep-exhep-phnucl-exRept.Prog.Phys.(2019)·57 citations
17. 17*

    The role of hidden symmetries and Kaluza-Klein mass generation in extra-dimensional gauge theories

    H. Novales-Sánchez🇲🇽 · J. J. Toscano🇲🇽

    The transition from formulations with extra dimensions to Kaluza-Klein theories, aimed at extending the Standard Model, bears the ingredients of hidden symmetries and the Kaluza-Klein mechanism for mass generation. We explore these essential aspects in detail, and find that much can be said about them with no reference to the specific geometry of compact extra dimensions: the low-energy theory is determined, included dynamic variables and symmetries; mass terms arise; eigenfunctions that define Kaluza-Klein fields are fixed by the appropriate choice a Casimir invariant; there is a set of Kaluza-Klein pseudo-Goldstone bosons. Throughout our presentation, similarities and differences among spontaneous symmetry breaking, commonly present in conventional Standard Model extensions, and what happens in Kaluza-Klein theories are signaled and discussed.

    ↳ hep-thhep-ph1 citation

* 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.