Thu·Apr 21, 2016Thursday·April 21, 2016

1. 01*

   New ambiguity in probing CP violation in neutrino oscillations

   O. G. Miranda🇲🇽 · M. Tortola🇪🇸 · J. W. F. Valle🇪🇸

   If neutrinos get mass via the seesaw mechanism the mixing matrix describing neutrino oscillations can be effectively non-unitary. We show that in this case the neutrino appearance probabilities involve a new CP phase, phi, associated to non-unitarity. This leads to an ambiguity in extracting the "standard" three--neutrino phase delta_CP, which can survive even after neutrino and antineutrino channels are combined. Its existence should be taken into account in the planning of any oscillation experiment aiming at a robust measurement of delta_CP.

   hep-phhep-exPRL(2016)·74 citations
2. 02*

   Baryon Number, Lepton Number, and Operator Dimension in the Standard Model

   Andrew Kobach🇺🇸

   We prove that for a given operator in the Standard Model (SM) with baryon number B and lepton number L, that the operator's dimension is even (odd) if (B-L)/2 is even (odd). Consequently, this establishes the veracity of statements that were long observed or expected to be true, but not proven, e.g., operators with B-L=0 are of even dimension, B-L must be an even number, etc. These results remain true even if the SM is augmented by any number of right-handed neutrinos with L=1.

   hep-phPLB(2016)·153 citations
3. 03*

   A Cautionary Tale of Mis-measured Tails from $q/g$ Bias

   Adam Martin🇺🇸 · Tuhin S. Roy🇮🇳

   Jet substructure techniques such as subjet $p_T$-asymmetry, mass-drop, and grooming have become powerful and widely used tools in experimental searches at the LHC. While these tools provide much-desired handles to separate signal from background, they can introduce unexpected mass scales into the analysis. These scales may be misinterpreted as excesses if these are not correctly incorporated into background modeling. As an example, we study the ATLAS hadronic di-$W/Z$ resonance search. There, we find that the substructure analysis -- in particular the combination of a subjet asymmetry cut with the requirement on the number of tracks within a jet -- induces a mass scale where the dominant partonic subprocess in the background changes from $pp\to g+q/\bar{q}$ to $pp\to q\bar{q}$. In light of this scale, modeling the QCD background using a simple smooth function with monotonically decreasing slope appears insufficient.

   hep-phhep-exPRD(2016)·5 citations
4. 04*

   Implications of perturbative unitarity for scalar di-boson resonance searches at LHC

   Luca Di Luzio🇮🇹 · Jernej F. Kamenik🇸🇮 · Marco Nardecchia🇬🇧

   We study the constraints implied by partial wave unitarity on new physics in the form of spin-zero di-boson resonances at LHC. We derive the scale where the effective description in terms of the SM supplemented by a single resonance is expected to break down depending on the resonance mass and signal cross-section. Likewise, we use unitarity arguments in order to set perturbativity bounds on renormalizable UV completions of the effective description. We finally discuss under which conditions scalar di-boson resonance signals can be accommodated within weakly-coupled models.

   hep-phEPJC(2017)·82 citations
5. 05*

   Generalized mass ordering degeneracy in neutrino oscillation experiments

   Pilar Coloma🇺🇸 · Thomas Schwetz🇩🇪

   We consider the impact of neutral-current (NC) non-standard neutrino interactions (NSI) on the determination of the neutrino mass ordering. We show that in presence of NSI there is an exact degeneracy which makes it impossible to determine the neutrino mass ordering and the octant of the solar mixing angle ${\theta }_{12}$ at oscillation experiments. The degeneracy holds at the probability level and for arbitrary matter density profiles, and hence, solar, atmospheric, reactor, and accelerator neutrino experiments are affected simultaneously. The degeneracy requires order-one corrections from NSI to the NC neutrino--quark interaction and can be tested in neutrino--nucleus NC scattering experiments.

   hep-phhep-exPRD(2016)·131 citations
6. 06*

   The 750 GeV diphoton excess in a two Higgs doublet model and a singlet scalar model, with vector-like fermions, unitarity constraints, and dark matter implications

   Shrihari Gopalakrishna🇮🇳 · Tuhin Subhra Mukherjee🇮🇳

   We explore the possibility of a beyond the standard model scalar ($\varphi$) as a possible explanation of the diphoton resonance at 750~GeV invariant mass reported by the ATLAS and CMS collaborations at the large hadron collider (LHC). We first present in a model-independent way the scalar-gluon-gluon and scalar-photon-photon effective couplings needed for obtaining the required diphoton cross-section at the LHC for different total widths. We investigate here two new-physics possibilities that can generate these effective couplings, namely, (i) the 2-Higgs-doublet model (2HDM) in the alignment limit, and (ii) a singlet scalar, with vector-like fermions added and playing a crucial role in generating the effective couplings. We present the regions of model parameter space which are allowed by direct LHC and perturbative unitarity constraints, and that give the required diphoton cross-section at the LHC for various total widths. In the singlet case, we include the possibility that $\varphi$ decays into a pair of neutral stable vector-like fermions that could be dark matter. We find regions of parameter-space of the singlet model that gives the required diphoton rate, have the correct dark matter relic-density, have dark matter direct-detection rates compatible with current direct-detection experiments, and satisfy LHC bounds and perturbative unitarity constraints.

   hep-ph19 citations
7. 07*

   Composite Weak Bosons at the Large Hadronic Collider

   Harald Fritzsch🇩🇪

   In a composite model of the weak bosons the p-wave bosons are studied. The state with the lowest mass is identified with the boson, which has been discovered at the LHC. Specific properties of the excited bosons are discussed, in particular their decays into weak bosons and photons. Recently a two photon signal has been observed, which might come from the decay of a neutral heavy boson with a mass of about 0.75 TeV. This particle could be an excited weak tensor boson.

   hep-phMod.Phys.Lett.A(2016)·11 citations
8. 08*

   Magnetic properties of ground-state mesons

   Vytautas Simonis🇱🇹

   Starting with the bag model a method for the study of the magnetic properties (magnetic moments, magnetic dipole transition widths) of ground-state mesons is developed. We calculate the M1 transition moments and use them subsequently to estimate the corresponding decay widths. These are compared with experimental data, where available, and with the results obtained in other approaches. Finally, we give the predictions for the static magnetic moments of all ground-state vector mesons including those containing heavy quarks. We have a good agreement with experimental data for the M1 decay rates of light as well as heavy mesons. Therefore, we expect our predictions for the static magnetic properties (usual magnetic moments) to be of sufficiently high quality, too.

   hep-phEPJA(2016)·45 citations
9. 09*

   Lorentz and CPT violation in the Standard-Model Extension

   Ralf Lehnert🇺🇸

   Lorentz and CPT invariance are among the symmetries that can be investigated with ultrahigh precision in subatomic physics. Being spacetime symmetries, Lorentz and CPT invariance can be violated by minuscule amounts in many theoretical approaches to underlying physics that involve novel spacetime concepts, such as quantized versions of gravity. Regardless of the underlying mechanism, the low-energy effects of such violations are expected to be governed by effective field theory. This talk provides a survey of this idea and includes an overview of experimental efforts in the field.

   hep-phHyperfine Interact.(2013)·5 citations
10. 10*

    Thermal properties and evolution of the $U_A(1)$ factor for 2+1 flavors

    G. Fejos🇯🇵 · A. Hosaka🇯🇵

    Thermal evolution of the axial anomaly is investigated in the system of the linear sigma model for $2+1$ flavors. We explore the functional form of the effective potential and the coefficient of the `t Hooft determinant term. It is found that the latter develops a non-trivial structure as a function of the chiral condensate and grows everywhere with respect to the temperature. This shows that mesonic fluctuations strengthen the axial anomaly at finite temperature and it does not get vanished at the critical point. The phenomenon has been found to have significance in the thermal properties of the mesonic spectra, especially concerning the $\eta -{\eta }^{\prime }$ system.

    hep-phPRD(2016)·36 citations
11. 11*

    Generalization of the Majorana equation for real spinors

    Ginés R. Pérez Teruel🇪🇸

    We show that the Dirac equation for real spinors can be naturally decomposed into a system of two first-order relativistic wave equations. The decomposition separates in a transparent way the real and imaginary parts of the Dirac equation by means of two algebraic differential operators, allowing to describe real spinors in any representation of the Dirac matrices maintaining the reality condition $\tilde{\Psi }={\tilde{\Psi }}^{\ast }$ unaltered. In addition, it is shown that the Majorana wave equation is a particular case of the relativistic system of equations deduced in this paper. We also briefly discuss how the formalism can be extended to deal with complex (charged) spinors.

    hep-phhep-th0 citations
12. 12*

    Scale-Invariant Models with One-Loop Neutrino Mass and Dark Matter Candidates

    Amine Ahriche🇩🇿 · Adrian Manning🇦🇺 · Kristian L. McDonald🇦🇺 · Salah Nasri🇦🇪

    We construct a list of minimal scale-invariant models at the TeV scale that generate one-loop neutrino mass and give viable dark matter candidates. The models generically contain a singlet scalar and a $Z_2$-odd sector comprised of singlet, doublet and/or triplet SU(2) multiplets. The dark matter may reside in a single multiplet or arise as an admixture of several multiplets. We find fifteen independent models, for which the dark matter is a viable candidate and neutrino mass results from a diagram with just one of the irreducible scale-invariant one-loop topologies. Further "non-pure" cases give hybrid one-/two-loop masses. All models predict new TeV scale physics, including a singlet scalar that generically mixes with the Higgs boson.

    hep-phPRD(2016)·51 citations
13. 13*

    High-order Primordial Perturbations with Quantum Gravitational Effects

    Tao Zhu🇨🇳 · Anzhong Wang🇨🇳 · Klaus Kirsten🇺🇸 · Gerald Cleaver🇺🇸 · Qin Sheng🇺🇸

    In this paper, we provide a systematic investigation of high-order primordial perturbations with nonlinear dispersion relations due to quantum gravitational effects in the framework of {\em uniform asymptotic approximations}. Because of these effects, the equation of motion of the mode function in general has multiple-turning points. After obtaining analytically approximated solutions to any order in different regions, associated with different types of turning points, we match them to the third one. To this order the errors are less than $0.15\%$. General expressions of the power spectra of the primordial tensor and scalar perturbations are derived explicitly. We also investigate effects of back-reactions of the quantum gravitational corrections, and make sure that inflation lasts long enough in order to solve the underlying problems, such as flatness, horizon and monopole. Then, we study various features of the spectra that are observationally relevant. In particular, under a moderate assumption about the energy scale of the underlying theory of quantum gravity, we have shown that the quantum gravitational effects may alter significantly the ratio between the tensor and scalar power spectra, thereby providing a natural mechanism to alleviate the tension between observations and certain inflationary models, including the one with a quadratic potential.

    ↳ gr-qcastro-ph.COhep-phhep-thPRD(2016)·31 citations
14. 14*

    Turning the LHC Ring into a New Physics Search Machine

    Matti Kalliokoski🇨🇭 · Jerry W. Lämsä🇺🇸 · Mikael Mieskolainen🇫🇮 · Risto Orava🇫🇮

    By combining the LHC Beam Loss Monitoring (BLM) system with the LHC experiments, a powerful search machine for new physics beyond the standard model can be realised. The pair of final state protons in the central production process, exit the LHC beam vacuum chamber at locations determined by their fractional momentum losses and will be detected by the BLM detectors. By mapping out the coincident pairs of the BLM identified proton candidates around the four LHC interaction regions, a scan for centrally produced particle states can be made independently of their decay modes.

    ↳ hep-exhep-ph12 citations
15. 15*

    Fixed point structure of the Abelian Higgs model

    G. Fejos🇯🇵 · T. Hatsuda🇯🇵

    The order of the superconducting phase transition is analyzed via the functional renormalization group approach. For the first time, we derive fully analytic expressions for the $\beta$ functions of the charge and the self-coupling in the Abelian Higgs model with one complex scalar field in $d=3$ dimensions that support the existence of two charged fixed points: an infrared (IR) stable fixed point describing a second-order phase transition and a tritical fixed point controlling the region of the parameter space that is attracted by the former one. It is found that the region separating first- and second-order transitions can be uniquely characterized by the Ginzburg-Landau parameter $\kappa$, and the system undergoes a second order transition, only if $\kappa >{\kappa }_c\approx 0.62/\sqrt{2}$.

    ↳ cond-mat.supr-conhep-phnucl-thPRD(2016)·10 citations
16. 16*

    Photoproduction of hidden-charm states in the $\gamma p\to {\bar{D}}^{\ast 0}{\Lambda }_c^{+}$ reaction near threshold

    Yin Huang🇨🇳 · Ju-Jun Xie🇨🇳 · Jun He🇨🇳 · Xurong Chen🇨🇳 · Hong-Fei Zhang🇨🇳

    We report on a theoretical study of the hidden charm $N_{c\bar{c}}^{\ast }$ states in the $\gamma p\to {\bar{D}}^{\ast 0}{\Lambda }_c^{+}$ reaction near threshold within an effective Lagrangian approach. In addition to the contributions from the $s$-channel nucleon pole, the $t$-channel $D^0$ exchange, the $u$-channel ${\Lambda }_c^{+}$ exchange and the contact term, we study the contributions from the $N_{c\bar{c}}^{\ast }$ states with spin-parity $J^P=1/2^{-}$ and $3/2^{-}$. The total and differential cross sections of the $\gamma p\to {\bar{D}}^{\ast 0}Lambd{a}_c^{+}$ reaction are predicted. It is found that the contributions of these $N_{c\bar{c}}^{\ast }$ states give clear peak structures in the total cross sections. Thus, this reaction is another new platform to study the hidden-charm states. It is expected that our model calculation may be tested by the future experiments.

    ↳ nucl-thhep-phnucl-exCPC(2016)·38 citations
17. 17*

    Critical Number of Fields in Stochastic Inflation

    Vincent Vennin🇬🇧 · Hooshyar Assadullahi🇬🇧 · Hassan Firouzjahi🇮🇷 · Mahdiyar Noorbala🇮🇷 · David Wands🇬🇧

    Stochastic effects in generic scenarios of inflation with multiple fields are investigated. First passage time techniques are employed to calculate the statistical moments of the number of inflationary $e$-folds, which give rise to all correlation functions of primordial curvature perturbations through the stochastic $\delta N$ formalism. The number of fields is a critical parameter. The probability of exploring arbitrarily large-field regions of the potential becomes non-vanishing when more than two fields are driving inflation. The mean number of $e$-folds can be infinite, depending on the number of fields; for plateau potentials, this occurs even with one field. In such cases, correlation functions of curvature perturbations are infinite. They can, however, be regularised if a reflecting (or absorbing) wall is added at large energy or field value. The results are found to be independent of the exact location of the wall and this procedure is, therefore, well-defined for a wide range of cutoffs, above or below the Planck scale. Finally, we show that, contrary to single-field setups, multi-field models can yield large stochastic corrections even at sub-Planckian energy, opening interesting prospects for probing quantum effects on cosmological fluctuations.

    ↳ astro-ph.COgr-qchep-phhep-thPRL(2017)·70 citations
18. 18*

    Inflationary universe from higher derivative quantum gravity coupled with scalar electrodynamics

    Ratbay Myrzakulov🇰🇿 · Sergei Odintsov🇪🇸 · Lorenzo Sebastiani🇰🇿

    We study inflation for a quantum scalar electrodynamics model in curved space-time and for higher-derivative quantum gravity (QG) coupled with scalar electrodynamics. The corresponding renormalization-group (RG) improved potential is evaluated for both theories in Jordan frame where non-minimal scalar-gravitational coupling sector is explicitly kept. The role of one-loop quantum corrections is investigated by showing how these corrections enter in the expressions for the slow-roll parameters, the spectral index and the tensor-to-scalar ratio and how they influence the bound of the Hubble parameter at the beginning of the primordial acceleration. We demonstrate that the viable inflation maybe successfully realized, so that it turns out to be consistent with last Planck and BICEP2/Keck Array data.

    ↳ hep-thgr-qchep-phNPB(2016)·24 citations
19. 19*

    Black Hole Spindown by Light Bosons

    Andrei Gruzinov🇺🇸

    The saturation mechanism for the fastest-growing instability of massive scalar field in Kerr metric is identified, assuming saturation by cubic or quartic nonlinearities of the field potential. The resulting spindown rate of the black hole is calculated. The (rather involved) saturation scenario is confirmed by numerical simulations.

    ↳ astro-ph.HEgr-qchep-ph46 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.