Mon·Jan 4, 2016Monday·January 4, 2016

1. 01*

   Thermalization of mini-jets in a quark-gluon plasma

   Edmond Iancu🇫🇷 · Bin Wu🇺🇸

   We present the complete physical picture for the evolution of a high-energy jet propagating through a weakly-coupled quark-gluon plasma (QGP) by analytical and numerical investigation of thermalization of the soft components of the jet. Our results support the following physical picture: the leading particle emits a significant number of mini-jets which promptly evolve via multiple branching and thus degrade into a myriad of soft gluons, with energies of the order of the medium temperature $T$. Via elastic collisions with the medium constituents, these soft gluons relax to local thermal equilibrium with the plasma over a time scale which is considerably shorter than the typical lifetime of the mini-jet. The thermalized gluons form a tail which lags behind the hard components of the jet. Together with the background QGP, they behave hydrodynamically.

   hep-phhep-exnucl-exnucl-thNPA(2016)·0 citations
2. 02*

   New Physics Patterns in ${\epsilon }^{\prime }/\epsilon$ and ${\epsilon }_K$ with Implications for Rare Kaon Decays and $\Delta M_K$

   Andrzej J. Buras🇩🇪

   The SM prediction for the ratio ${\epsilon }^{\prime }/\epsilon$ appears to be significantly below the experimental data. Also ${\epsilon }_K$ in the SM tends to be below the data. Any NP removing these anomalies will first of all have impact on flavour observables in the $K$ meson system, in particular on rare $K$ decays and $\Delta M_K$. Restricting the operators contributing to ${\epsilon }^{\prime }/\epsilon$ to the SM ones and to the corresponding primed operators, NP contributions are quite generally dominated either by QCD penguin (QCDP) operators $Q_6(Q_6^{\prime })$ or electroweak penguin (EWP) operators $Q_8(Q_8^{\prime })$ with rather different implications for other flavour observables. We discuss general models with tree-level $Z$ and $Z^{\prime }$ flavour violating exchanges and few specific models. We find that simultaneous enhancements of ${\epsilon }^{\prime }/\epsilon$, ${\epsilon }_K$, $\mathcal{B}(K_L\to {\pi }^0\nu \bar{\nu })$ and $\mathcal{B}(K^{+}\to {\pi }^{+}\nu \bar{\nu })$ in $Z$ scenarios are only possible in the presence of both LH and RH flavour-violating couplings. In $Z^{\prime }$ scenarios this is not required but the size of NP effects and the correlation between $\mathcal{B}(K_L\to {\pi }^0\nu \bar{\nu })$ and $\mathcal{B}(K^{+}\to {\pi }^{+}\nu \bar{\nu })$ depends strongly on whether QCDP or EWP dominate NP contributions to ${\epsilon }^{\prime }/\epsilon$. In the QCDP case possible enhancements of both branching ratios are much larger than for EWP scenario and take place only on the branch parallel to the Grossman-Nir bound, which is in the case of EWP dominance only possible in the absence of NP in ${\epsilon }_K$. QCDP and EWP scenarios of NP in ${\epsilon }^{\prime }/\epsilon$ can also be uniquely distinguished by the size and the sign of NP contribution to $\Delta M_K$, elevating the importance of the precise calculation of $\Delta M_K$ in the SM.

   hep-phhep-exhep-latJHEP(2016)·80 citations
3. 03*

   How Resonance-Continuum Interference Changes 750 GeV Diphoton Excess: Signal Enhancement and Peak Shift

   Sunghoon Jung🇺🇸 · Jeonghyeon Song🇰🇷 · Yeo Woong Yoon🇰🇷

   The new scalar resonance contribution to the 750 GeV diphoton excess observed at the LHC 13 TeV necessarily interferes with the continuum background in the $gg\to \gamma \gamma$. The interference has two considerable effects: (1) enhancing or suppressing diphoton signal rate due to the imaginary-part interference and (2) distorting resonance shape due to the real-part interference. From the best-fit study of two benchmark models (two Higgs doublets with $\sim$50 GeV widths and a singlet scalar with 5 GeV width, both extended with vector-like fermions), we find that the resonance contribution to the 750 GeV excess can be enhanced by a factor of 2(1.6) for 3(6) fb signal rate and the 68%(95%) CL best-fit mass range can shift by 1-4 (any $\mathcal{O}$(1)) GeV. If the best-fit excess rate decreases with future data, the interference effects will become more significant. The inevitable interferences can also provide a consistency check of a resonance hypothesis, whether or not future precision shape measurements confirm a Breit-Wigner shape or discover interesting deviations.

   hep-phhep-exJHEP(2016)·59 citations
4. 04*

   Soft-collinear effective theory for hadronic and nuclear collisions: The evolution of jet quenching from RHIC to the highest LHC energies

   Ivan Vitev🇺🇸

   In the framework of soft-collinear effective theory with Glauber gluons, results and predictions for inclusive hadron suppression, based upon in-medium parton shower evolution, are presented for Au+Au and Pb+Pb collisions at RHIC and LHC energies $\sqrt{s}=200$ AGeV and $\sqrt{s}=2.76,5.1$ ATeV, respectively. The $\mathrm{SCE}{\mathrm{T}}_{\mathrm{G}}$ medium-induced splitting kernels are further implemented to evaluate the attenuation of reconstructed jet cross in such reactions and to examine their centrality and radius $R$ dependence. Building upon a previously developed method to systematically resum the jet shape at next-to-leading logarithmic accuracy, a quantitative understanding of the jet shape modification measurement in Pb+Pb collisions at $\sqrt{s}=2.76$ ATeV at the LHC can be achieved. Predictions for photon-tagged jet cross sections and shapes, that can shed light on the parton flavor dependence of in-medium parton shower modification, are also given.

   hep-phnucl-thNPA(2016)·0 citations
5. 05*

   The ${\Lambda }_b\to J/\psi K^0\Lambda$ reaction and a hidden-charm pentaquark state with strangeness

   Jun-Xu Lu🇨🇳 · En Wang🇨🇳 · Ju-Jun Xie🇨🇳 · Li-Sheng Geng🇨🇳 · Eulogio Oset🇪🇸

   We study the ${\Lambda }_b\to J/\psi K^0\Lambda$ reaction considering both the $K^0\Lambda$ interaction with its coupled channels and the $J/\psi \Lambda$ interaction. The latter is described by taking into account the fact that there are predictions for a hidden-charm state with strangeness that couples to $J/\psi \Lambda$. By using the coupling of the resonance to $J/\psi \Lambda$ from these predictions we show that a neat peak can be observed in the $J/\psi \Lambda$ invariant mass distribution, rather stable under changes of unknown magnitudes. In some cases, one finds a dip structure associated to that state, but a signal of the state shows up in the $J/\psi$ spectrum.

   hep-phhep-exPRD(2016)·94 citations
6. 06*

   Dark matter and localised fermions from spherical orbifolds?

   Giacomo Cacciapaglia🇫🇷 · Aldo Deandrea🇫🇷 · Nicolas Deutschmann🇫🇷

   We study a class of six-dimensional models based on positive curvature surfaces (spherical 2-orbifolds) as extra-spaces. Using the Newman-Penrose formalism, we discuss the particle spectrum in this class of models. The fermion spectrum problem, which has been addressed with flux compactifications in the past, can be avoided using localised fermions. In this framework, we find that there are four types of geometry compatible with the existence of a stable dark matter candidate and we study the simplest case in detail. Using the complementarity between collider resonance searches and relic density constraints, we show that this class of models is under tension, unless the model lies in a funnel region characterised by a resonant Higgs s-channel in the dark matter annihilation.

   hep-phhep-thJHEP(2016)·9 citations
7. 07*

   Calculating Masses of Pentaquarks Composed of Baryons and Mesons

   Majid Monemzadeh🇮🇷 · Narges Tazimi · Shahnaz Babaghodrat🇮🇷

   In this paper, we consider an exotic baryon (pentaquark) as a bound state of two-particle systems composed of a baryon (nucleon) and a meson.We used a baryon - meson picture to reduce a complicated five-body problem to a simple two-body problems. The homogeneous Lippmann-Schwinger integral equation is solved in configuration space by using one pion exchange potential. We calculate the masses of pentaquarks ${\theta }_c(uudd\bar{c})$, ${\theta }_b(uudd\bar{b})$.

   hep-phnucl-thAdv.High Energy Phys.(2016)·14 citations
8. 08*

   Allowed rare pion and muon decays as tests of the Standard Model

   Dinko Pocanic (PEN Collaboration)🇺🇸

   Simple dynamics, few available decay channels, and extremely well controlled radiative and loop corrections, make pion and muon decays a sensitive means for testing the underlying symmetries, the universality of weak fermion couplings, as well as for study of pion structure and chiral dynamics. We review the current state of experimental study of the allowed rare decays of charged pions: (a) electronic, ${\pi }^{+}\to e^{+}{\nu }_e$, or ${\pi }_{e2}$, (b) radiative, ${\pi }^{+}\to e^{+}{\nu }_e\gamma$, or ${\pi }_{e2\gamma }$, and (c) semileptonic, ${\pi }^{+}\to {\pi }^0{e}^{+}\nu$, or ${\pi }_{e3}$, as well as muon radiative decay, ${\mu }^{+}\to e^{+}{\nu }_{\text{e}}{\bar{\nu }}_{\mu }\gamma$. Taken together, these data present an internally consistent picture that also agrees well with Standard Model (SM) predictions. However, even following the great strides of the recent decades, experimental accuracy is lagging far behind that of the theoretical description for all above processes. We review the implications of the present state of knowledge and prospects for further improvement in the near term.

   ↳ nucl-exhep-exhep-ph3 citations
9. 09*

   An Evidence of Mass Dependent Differential Kinetic Freeze-out Scenario Observed in Pb-Pb Collisions at 2.76 TeV

   Hai-Ling Lao🇨🇳 · Hua-Rong Wei🇨🇳 · Fu-Hu Liu🇨🇳 · Roy A. Lacey🇺🇸

   Transverse momentum spectra of different particles produced in mid-rapidity interval in lead-lead (Pb-Pb) collisions with different centrality intervals, measured by the ALICE Collaboration at center-of-mass energy per nucleon pair $\sqrt{s_{NN}}=2.76$ TeV, are conformably and approximately described by the Tsallis distribution. The dependences of parameters (effective temperature, entropy index, and normalization factor) on event centrality and particle rest mass are obtained. The source temperature at the kinetic freeze-out is obtained to be the intercept in the linear relation between effective temperature and particle rest mass, while the particle transverse flow velocity is approximately extracted to be the slope in the linear relation between mean transverse momentum and particle rest mass. It is shown that the source temperature increases with increase of particle rest mass, which exhibits an evidence of mass dependent differential kinetic freeze-out scenario or multiple kinetic freeze-out scenario.

   ↳ nucl-thhep-exhep-phnucl-exEPJA(2016)·46 citations
10. 10*

    Tracking Dark Energy from Axion-Gauge Field Couplings

    Stephon Alexander🇺🇸 · Robert Brandenberger🇨🇦 · Juerg Froehlich🇨🇭

    We propose a toy model of Dark Energy in which the degrees of freedom currently dominating the energy density of the universe are described by a pseudo-scalar "axion field" linearly coupled to the Pontryagin density, $\text{tr}(F\wedge F)$, i.e., the exterior derivative of the Chern-Simons form, of a gauge field. We assume that the axion has self-interactions corresponding to an exponential potential. We argue that a non-vanishing magnetic helicity of the gauge field leads to slow-rolling of the axion at field values far below the Planck scale. Our proposal suggests a "Tracking Dark Energy Scenario" in which the contribution of the axion energy density to the total energy density is constant (and small), during the early radiation phase, until a secular growth term proportional to the Pontryagin density of the gauge field becomes dominant. The initially small contribution of the axion field to the total energy density is related to the observed small baryon-to-entropy ratio.

    ↳ hep-thastro-ph.COgr-qchep-ph11 citations
11. 11*

    Fractionized Skyrmions in Dense Compact-Star Matter

    Masayasu Harada🇯🇵 · Hyun Kyu Lee🇰🇷 · Yong-Liang Ma🇨🇳 · Mannque Rho🇫🇷

    The hadronic matter described as a skyrmion matter embedded in an FCC crystal is found to turn into a half-skyrmion matter with vanishing (in the chiral limit) quark condensate and {\it non-vanishing} pion decay constant {$f_{\pi }$} at a density $n_{1/2}$ lower than or near the critical density $n_c$ at which hadronic matter changes over to a chiral symmetry restored phase with possibly deconfined quarks. When hidden local gauge fields and a dilaton scalar of spontaneously broken scale symmetry with decay constant $f_{\chi }$ are incorporated, this half-skyrmion phase is characterized by $f_{\chi }\approx f_{\pi }\ne 0$ with the hidden gauge coupling $g\ne 0$ but $\ll 1$. While chiral symmetry is restored {\it globally} in this region in the sense that space-averaged, $\text{la}\bar{q}q\text{ra}$ vanishes, quarks are still confined in massive hadrons and massless pions. This phase is shown to play a crucial role in the model for a smooth transition from a soft EoS at low density to a stiffer EoS at high density, the changeover taking place at $n_{1/2}\sim 2n_0$. It resembles the "quarkyonic phase" predicted in large $N_c$ QCD and represents the "hadronic freedom" regime which figures as a doorway to chiral restoration. The fractionization of skyrmion matter into half-skyrmion matter has a tantalizing analogy to what appears to happen in condensed matter in (2+1) dimensions where half-skyrmions or "merons" enter as relevant degrees of freedom at the interface.

    ↳ nucl-thhep-ph5 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.