Fri·Feb 19, 2016Friday·February 19, 2016

1. 01*

   Present Status of Single Pion Production in Neutrino-Nucleus Reactions

   L. Alvarez-Ruso🇪🇸 · E. Hernandez🇪🇸 · J. Nieves🇪🇸 · M. J. Vicente Vacas🇪🇸

   Some of the recent progress in the physics of pion production induced by neutrinos on nucleons and nuclei is reviewed from a theoretical perspective. The importance of Watson's theorem to reconcile ANL and BNL data with the off-diagonal Goldberger-Treiman relation for the $\Delta (1232)$ is discussed. The disagreement between MiniBooNE data and theoretical calculations is presented in the light of the new MINERvA data. The coherent pion production data on ${}^{12}$C obtained by MINERvA are also compared to different microscopic and PCAC models.

   hep-phhep-exnucl-thJPS Conf.Proc.(2016)·4 citations
2. 02*

   Precision tools and models to narrow in on the 750 GeV diphoton resonance

   Florian Staub🇨🇭 · Peter Athron🇦🇺 · Lorenzo Basso🇫🇷 · Mark D. Goodsell🇫🇷 · Dylan Harries🇦🇺 · Manuel E. Krauss🇩🇪 · Kilian Nickel🇩🇪 · Toby Opferkuch🇩🇪 · Lorenzo Ubaldi🇮🇱 · Avelino Vicente🇪🇸 · Alexander Voigt🇩🇪

   The hints for a new resonance at 750 GeV from ATLAS and CMS have triggered a significant amount of attention. Since the simplest extensions of the standard model cannot accommodate the observation, many alternatives have been considered to explain the excess. Here we focus on several proposed renormalisable weakly-coupled models and revisit results given in the literature. We point out that physically important subtleties are often missed or neglected. To facilitate the study of the excess we have created a collection of 40 model files, selected from recent literature, for the Mathematica package SARAH. With SARAH one can generate files to perform numerical studies using the tailor-made spectrum generators FlexibleSUSY and SPheno. These have been extended to automatically include crucial higher order corrections to the diphoton and digluon decay rates for both CP-even and CP-odd scalars. Additionally, we have extended the UFO and CalcHep interfaces of SARAH, to pass the precise information about the effective vertices from the spectrum generator to a Monte-Carlo tool. Finally, as an example to demonstrate the power of the entire setup, we present a new supersymmetric model that accommodates the diphoton excess, explicitly demonstrating how a large width can be obtained. We explicitly show several steps in detail to elucidate the use of these public tools in the precision study of this model.

   hep-phEPJC(2016)·105 citations
3. 03*

   Vacuum Stability and Radiative Electroweak Symmetry Breaking in an SO(10) Dark Matter Model

   Yann Mambrini🇫🇷 · Natsumi Nagata🇺🇸 · Keith A. Olive🇺🇸 · Jiaming Zheng🇺🇸

   Vacuum stability in the Standard Model is problematic as the Higgs quartic self-coupling runs negative at a renormalization scale of about $10^{10}$ GeV. We consider a non-supersymmetric SO(10) grand unification model for which gauge coupling unification is made possible through an intermediate scale gauge group, $G_{\text{int}}=\text{SU}(3{)}_C\otimes \text{SU}(2{)}_L\otimes \text{SU}(2{)}_R\otimes \text{U}(1{)}_{B-L}$. $G_{\text{int}}$ is broken by the vacuum expectation value of a 126 of SO(10) which not only provides for neutrino masses through the seesaw mechanism but also preserves a discrete ${\mathbb{Z}}_2$ that can account for the stability of a dark matter candidate, here taken to be the Standard Model singlet component of a bosonic 16. We show that in addition to these features the model insures the positivity of the Higgs quartic coupling through its interactions to the dark matter multiplet and 126. We also show that the Higgs mass squared runs negative triggering electroweak symmetry breaking. Thus, the vacuum stability is achieved along with radiative electroweak symmetry breaking and captures two more important elements of supersymmetric models without low-energy supersymmetry. The conditions for perturbativity of quartic couplings and for radiative electroweak symmetry breaking lead to tight upper and lower limits on the dark matter mass, respectively, and this dark matter mass region (1.35-2 TeV) can be probed in future direct detection experiments.

   hep-phPRD(2016)·51 citations
4. 04*

   LHC 750 GeV diphoton excess and muon $(g-2)$

   Seungwon Baek🇰🇷 · Jae-hyeon Park🇰🇷

   We consider implications of the diphoton excess recently observed at the LHC on the anomalous magnetic dipole moment of the muon $(g-2{)}_{\mu }=2a_{\mu }$, hypothesizing that the possible 750 GeV resonance is a (pseudo)scalar particle. The (pseudo)scalar-$\gamma$-$\gamma$ interaction implied by the diphoton events might generically contribute to $a_{\mu }$ via 2-loop Barr-Zee type diagrams in a broad class of models. If the scalar is an $SU(2{)}_L$ singlet, the new contribution to $a_{\mu }$ is much smaller than the current anomaly, $\Delta a_{\mu }\equiv a_{\mu }^{\exp }-a_{\mu }^{\mathrm{SM}}\approx (30\pm 10)\times 10^{-10}$, since the scalar can complete the Barr-Zee diagrams only through its mixing with the Standard Model Higgs boson. If the (pseudo)scalar belongs to an $SU(2{)}_L$ doublet in an extended Higgs sector, then by contrast, $\Delta a_{\mu }$ can be easily accommodated with the aid of an enhanced Yukawa coupling of the (pseudo)scalar to the muon such as in the Type-II or -X two Higgs doublet model.

   hep-phPLB(2016)·20 citations
5. 05*

   WIMP Dark Matter in Composite Higgs Models and the Dilaton Portal

   Manki Kim🇰🇷 · Seung J. Lee🇰🇷 · Alberto Parolini🇰🇷

   We study under which conditions a scalar particle is a viable WIMP Dark Matter candidate with Higgs and dilaton interactions. The theory is a composite Higgs model with top partial compositeness where both the Higgs and the Dark Matter candidate arise as pseudo Goldstone boson of the coset SO(6)/SO(5) from a new physics sector. We highlight the role of the dilaton in direct and indirect searches. We find that a Dark Matter particle with a mass around 200-400 GeV and a relatively light dilaton are a fair prediction of the model.

   hep-ph25 citations
6. 06*

   A comparison of NNLO QCD predictions with 7 TeV ATLAS and CMS data for $V$+jet processes

   Radja Boughezal🇺🇸 · Xiaohui Liu🇺🇸 · Frank Petriello🇺🇸

   We perform a detailed comparison of next-to-next-to-leading order (NNLO) QCD predictions for the W+jet and Z+jet processes with 7 TeV experimental data from ATLAS and CMS. We observe excellent agreement between theory and data for most studied observables, which span several orders of magnitude in both cross section and energy. For some observables, such as the $H_T$ distribution, the NNLO QCD corrections are essential for resolving existing discrepancies between theory and data.

   hep-phhep-exPLB(2016)·38 citations
7. 07*

   High-energy electroproduction in an atomic field

   P. A. Krachkov🇷🇺 · A. I. Milstein🇷🇺

   The differential cross section of high-energy electroproduction in the electric field of heavy atoms is derived. The result is obtained with the exact account of the atomic field by means of the quasiclassical approximation to the wave functions in the external field. The Coulomb corrections substantially modify the differential cross section compared with the Born result. They lead to the azimuth asymmetry in the differential cross section for the polarized incoming electron. The Coulomb corrections to the total cross section are obtained in the leading logarithmic approximation.

   hep-phphysics.atom-phPRA(2016)·4 citations
8. 08*

   Confronting fluctuations of conserved charges in central nuclear collisions at the LHC with predictions from Lattice QCD

   P. Braun-Munzinger🇩🇪 · A. Kalweit🇨🇭 · K. Redlich🇵🇱 · J. Stachel🇩🇪

   We construct net baryon number and strangeness susceptibilities as well as correlations between electric charge, strangeness and baryon number from experimental data on the particle production yields at midrapidity of the ALICE Collaboration at CERN. The data were taken in central Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}$~=~2.76~TeV and cover one unit of rapidity. We show that the resulting fluctuations and correlations are consistent with Lattice QCD results at the chiral crossover pseudocritical temperature $T_c\simeq$ 155 MeV. This agreement lends strong support to the assumption that the fireball created in these collisions is of thermal origin and exhibits characteristic properties expected in QCD at the transition from the quark gluon plasma to the hadronic phase. Since Lattice QCD calculations are performed at a baryochemical potential of ${\mu }_B$ = 0, the comparisons with LHC data are the most direct due to the vanishing baryon transport to midrapidity at these high energies.

   hep-phhep-latnucl-thNPA(2016)·7 citations
9. 09*

   Double parton scattering and 3D proton structure: A Light-Front analysis

   Matteo Rinaldi🇮🇹 · Sergio Scopetta🇮🇹 · Marco Traini🇮🇹 · Vicente Vento🇪🇸

   Double parton scattering, occurring in high energy hadron-hadron collisions, e.g. at the LHC, is usually investigated through model dependent analyses of the so called effective cross section ${\sigma }_{eff}$. We present a dynamic approach to this fundamental quantity making use of a Light-Front model treatment. Within such a framework ${\sigma }_{eff}$ is initially evaluated at low energy scale using the model and then, through QCD evolution, at high energy scale to reach the experimental conditions. Our numerical outcomes are consistent with the present experimental analyses of data in kinematical region we investigate. An important result of the present work is the $x_i$ dependence of ${\sigma }_{eff}$, a feature directly connected to double parton correlations and which could unveil new information on the three dimensional structure of the proton.

   hep-phFew Body Syst.(2016)·0 citations
10. 10*

    Self Coupling of the Higgs boson in the processes $pp\to ZHHH+X$ and $pp\to WHHH+X$

    Duane A. Dicus🇺🇸 · Chung Kao🇺🇸 · Wayne W. Repko🇺🇸

    To gain some sense about the likelihood of measuring the Higgs boson quartic coupling, we calculate the contribution to the triple Higgs production cross section from the subprocesses $q\bar{q}\to ZHHH$ and $q{\bar{q}}^{\prime }\to WHHH$. Our results illustrate that determining this coupling, or even providing experimental evidence that it exists, will be very difficult.

    hep-phPRD(2016)·12 citations
11. 11*

    Signs of Composite Higgs Pair Production at Next-to-Leading Order

    Ramona Grober🇮🇹 · Margarete Muhlleitner🇩🇪 · Michael Spira🇨🇭

    In composite Higgs models the Higgs boson arises as a pseudo-Goldstone boson from a strongly-interacting sector. Fermion mass generation is possible through partial compositeness accompanied by the appearance of new heavy fermionic resonances. The Higgs couplings to the Standard Model (SM) particles and between the Higgs bosons themselves are modified with respect to the SM. Higgs pair production is sensitive to the trilinear Higgs self-coupling but also to anomalous couplings like the novel 2-Higgs-2-fermion coupling emerging in composite Higgs models. The QCD corrections to SM Higgs boson pair production are known to be large. In this paper we compute, in the limit of heavy loop particle masses, the next-to-leading order (NLO) QCD corrections to Higgs pair production in composite Higgs models without and with new heavy fermions. The relative QCD corrections are found to be almost insensitive both to the compositeness of the Higgs boson and to the details of the heavy fermion spectrum, since the leading order cross section dominantly factorizes. With the obtained results we investigate the question if, taking into account Higgs coupling constraints, new physics could first be seen in Higgs pair production. We find this to be the case in the high-luminosity option of the LHC for composite Higgs models with heavy fermions. We also investigate the invariant mass distributions at NLO QCD. While they are sensitive to the Higgs non-linearities and hence anomalous couplings, the influence of the heavy fermions is much less pronounced.

    hep-phJHEP(2016)·47 citations
12. 12*

    Physics of Core-Collapse Supernovae in Three Dimensions: a Sneak Preview

    H.-Thomas Janka (1)🇩🇪 · Tobias Melson (1,2)🇩🇪 · Alexander Summa (1) ((1) MPI Astrophysics, Garching, (2) Physik Dept., TUM, Garching)🇩🇪

    Nonspherical mass motions are a generic feature of core-collapse supernovae, and hydrodynamic instabilities play a crucial role for the explosion mechanism. First successful neutrino-driven explosions could be obtained with self-consistent, first-principle simulations in three spatial dimensions (3D). But 3D models tend to be less prone to explosion than corresponding axisymmetric (2D) ones. This has been explained by 3D turbulence leading to energy cascading from large to small spatial scales, inversely to the 2D case, thus disfavoring the growth of buoyant plumes on the largest scales. Unless the inertia to explode simply reflects a lack of sufficient resolution in relevant regions, it suggests that some important aspect may still be missing for robust and sufficiently energetic neutrino-powered explosions. Such deficits could be associated with progenitor properties like rotation, magnetic fields or pre-collapse perturbations, or with microphysics that could lead to an enhancement of neutrino heating behind the shock. 3D simulations have also revealed new phenomena that are not present in 2D, for example spiral modes of the standing accretion shock instability (SASI) and a stunning dipolar lepton-emission self-sustained asymmetry (LESA). Both impose time- and direction-dependent variations on the detectable neutrino signal. The understanding of these effects and of their consequences is still in its infancy.

    ↳ astro-ph.SRhep-phnucl-thAnn.Rev.Nucl.Part.Sci.(2016)·453 citations
13. 13*

    $\mu$-Distortions or Running: A Guaranteed Discovery from CMB Spectrometry

    Giovanni Cabass🇮🇹 · Alessandro Melchiorri🇮🇹 · Enrico Pajer🇳🇱

    We discuss the implications of a PIXIE-like experiment, which would measure $\mu$-type spectral distortions of the CMB at a level of ${\sigma }_{\mu }=(1/n)\times 10^{-8}$, with $n\ge 1$ representing an improved sensitivity (e.g. $n=10$ corresponds to PRISM). Using Planck data and considering the six-parameter $\Lambda$CDM model, we compute the posterior for ${\mu }_8\equiv \mu \times 10^8$ and find ${\mu }_8=1.57_{-0.13}^{+0.11}$ ($68\%\mathrm{CL}$). This becomes ${\mu }_8=1.28_{-0.52}^{+0.30}$ ($68\%\mathrm{CL}$) when the running ${\alpha }_{\mathrm{s}}$ of the spectral index is included. We point out that a sensitivity of about $3\times$ PIXIE implies a guaranteed discovery: $\mu$-distortion is detected or ${\alpha }_{\mathrm{s}}\ge 0$ is excluded (both at $95\%\mathrm{CL}$ or higher). This threshold sensitivity sets a clear benchmark for CMB spectrometry. For a combined analysis of PIXIE and current Planck data, we discuss the improvement on measurements of the tilt $n_{\mathrm{s}}$ and the running ${\alpha }_{\mathrm{s}}$ and the dependence on the choice of the pivot. A fiducial running of ${\alpha }_{\mathrm{s}}=-0.01$ (close to the Planck best-fit) leads to a detection of negative running at $2\sigma$ for $5\times$ PIXIE. A fiducial running of ${\alpha }_{\mathrm{s}}=-0.02$, still compatible with Planck, requires $3\times$ PIXIE to rule out ${\alpha }_{\mathrm{s}}=0$ (at $95\%\mathrm{CL}$). We propose a convenient and compact visualization of the improving constraints on the tilt, running and tensor-to-scalar ratio.

    ↳ astro-ph.COhep-phPRD(2016)·56 citations
14. 14*

    Fermionic influence (action) on inflationary fluctuations

    Daniel Boyanovsky🇺🇸

    Motivated by apparent persistent large scale anomalies in the CMB we study the influence of fermionic degrees of freedom on the dynamics of inflaton fluctuations as a possible source of violations of (nearly) scale invariance on cosmological scales. We obtain the non-equilibrium effective action of an inflaton-like scalar field with Yukawa interactions ($Y_{D,M}$) to light \emph{fermionic} degrees of freedom both for Dirac and Majorana fields in de Sitter space-time. The effective action leads to Langevin equations of motion for the fluctuations of the inflaton-like field, with self-energy corrections and a stochastic gaussian noise. We solve the Langevin equation in the super-Hubble limit implementing a dynamical renormalization group resummation. For a nearly massless inflaton its power spectrum of super Hubble fluctuations is \emph{enhanced}, $\mathcal{P}(k;\eta )=(\frac{H}{2\pi }{)}^2{e}^{{\gamma }_t[-k\eta ]}$ with ${\gamma }_t[-k\eta ]=\frac{1}{6{\pi }^2}[{\sum }_{i=1}^{N_D}{Y}_{i,D}^2+2{\sum }_{j=1}^{N_M}{Y}_{j,M}^2]\{{\ln }^2[-k\eta ]-2\ln [-k\eta ]\ln [-k{\eta }_0]\}$ for $N_D$ Dirac and $N_M$ Majorana fermions, and ${\eta }_0$ is the renormalization scale at which the inflaton mass vanishes. The full power spectrum is shown to be renormalization group invariant. These corrections to the super-Hubble power spectrum entail a violation of scale invariance as a consequence of the coupling to the fermionic fields. The effective action is argued to be \emph{exact} in a limit of large number of fermionic fields. A cancellation between the enhancement from fermionic degrees of freedom and suppression from light scalar degrees of freedom \emph{conformally coupled to gravity} suggests the possibility of a finely tuned \emph{supersymmetry} among these fields.

    ↳ gr-qcastro-ph.COhep-phhep-thPRD(2016)·22 citations
15. 15*

    NICA fixed target mode: soft jet studies in the relative 4-velocity space

    V. A. Okorokov (National Research Nuclear University MEPhI)🇷🇺

    Experimental results obtained by studying the properties of soft jets in the 4-velocity space at $\sqrt{s}\sim 2-20$ GeV are presented. The changes in the mean distance from the jet axis to the jet particles, the mean kinetic energy of these particles, and the cluster dimension in response to the growth of the collision energy are consistent with the assumption that quark degrees of freedom manifest themselves in processes of pion jet production at intermediate energies. The energy at which quark degrees of freedom begin to manifest themselves experimentally in the production of soft pion jets is estimated for the first time. The estimated value of this energy is $2.8\pm 0.6$ GeV. The suggestions are made for future investigations on NICA.

    ↳ hep-exhep-phEPJA(2016)·0 citations
16. 16*

    Pre-reheating Magnetogenesis in the Kinetic Coupling Model

    Tomohiro Fujita🇺🇸 · Ryo Namba🇯🇵

    Recent blazar observations provide growing evidence for the presence of magnetic fields in the extragalactic regions. While a natural speculation is to associate the production to inflationary physics, it has been known that magnetogenesis solely from inflation is quite challenging. We therefore study a model in which a non-inflaton field $\chi$ coupled to the electromagnetic field through its kinetic term, $-I^2(\chi )F^2/4$, continues to move after inflation until the completion of reheating. This leads to a post-inflationary amplification of the electromagnetic field. We compute all the relevant contributions to the curvature perturbation, including gravitational interactions, and impose the constraints from the CMB scalar fluctuations on the strength of magnetic fields. We, for the first time, explicitly verify both the backreaction and CMB constraints in a simple yet successful magnetogenesis scenario without invoking a dedicated low-scale inflationary model in the weak-coupling regime of the kinetic coupling model.

    ↳ astro-ph.COhep-phPRD(2016)·60 citations
17. 17*

    Testing the strong equivalence principle with the triple pulsar PSR J0337+1715

    Lijing Shao🇩🇪

    Three conceptually different masses appear in equations of motion for objects under gravity, namely, the inertial mass, $m_{\mathcal{I}}$, the passive gravitational mass, $m_{\mathcal{P}}$, and the active gravitational mass, $m_{\mathcal{A}}$. It is assumed that, for any objects, $m_{\mathcal{I}}=m_{\mathcal{P}}=m_{\mathcal{A}}$ in the Newtonian gravity, and $m_{\mathcal{I}}=m_{\mathcal{P}}$ in the Einsteinian gravity, oblivious to objects' sophisticated internal structure. Empirical examination of the equivalence probes deep into gravity theories. We study the possibility of carrying out new tests based on pulsar timing of the stellar triple system, PSR J0337+1715. Various machine-precision three-body simulations are performed, from which, the equivalence-violating parameters are extracted with Markov chain Monte Carlo sampling that takes full correlations into account. We show that the difference in masses could be probed to $3\times 10^{-8}$, improving the current constraints from lunar laser ranging on the post-Newtonian parameters that govern violations of $m_{\mathcal{P}}=m_{\mathcal{I}}$ and $m_{\mathcal{A}}=m_{\mathcal{P}}$ by thousands and millions, respectively. The test of $m_{\mathcal{P}}=m_{\mathcal{A}}$ would represent the first test of Newton's third law with compact objects.

    ↳ gr-qcastro-ph.HEhep-phPRD(2016)·28 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.