Mon·Apr 4, 2016Monday·April 4, 2016

1. 01*

   $K\to \pi {\ell }^{+}{\ell }^{-}$ form factor in the Large-N${}_c$ and cut-off regularization method

   E. Coluccio Leskow🇮🇹 · G. D'Ambrosio🇮🇹 · D. Greynat🇮🇹 · A. Nath🇮🇹

   Bardeen-Buras-Gérard have proposed a large N${}_c$ method to evaluate hadronic weak matrix elements to attack for instance the determination of the $\Delta I=\frac{1}{2}$-rule and $\mathrm{Re}(\frac{{ϵ}^{\prime }}{ϵ})$. Here we test this method to the determination of the form factor parameters $a_{+}$ and $b_{+}$ in the decays $K^{+}\to {\pi }^{+}{\ell }^{+}{\ell }^{-}$ and $K_S\to {\pi }^0{\ell }^{+}{\ell }^{-}$. The results are encouraging: in particular after a complete treatment of Vector Meson Dominance (VMD).

   hep-phPRD(2016)·13 citations
2. 02*

   Stop Search in the Compressed Region via Semileptonic Decays

   Hsin-Chia Cheng🇺🇸 · Christina Gao🇺🇸 · Lingfeng Li🇺🇸 · Nicolas A. Neill🇺🇸

   In supersymmetric extensions of the Standard Model, the superpartners of the top quark (stops) play the crucial role in addressing the naturalness problem. For direct pair-production of stops with each stop decaying into a top quark plus the lightest neutralino, the standard stop searches have difficulty finding the stop for a compressed spectrum where the mass difference between the stop and the lightest neutralino is close to the top quark mass, because the events look too similar to the large $t\bar{t}$ background. With an additional hard ISR jet, the two neutralinos from the stop decays are boosted in the opposite direction and they can give rise to some missing transverse energy. This may be used to distinguish the stop decays from the backgrounds. In this paper we study the semileptonic decay of such signal events for the compressed mass spectrum. Although the neutrino from the $W$ decay also produces some missing transverse energy, its momentum can be reconstructed from the kinematic assumptions and mass-shell conditions. It can then be subtracted from the total missing transverse momentum to obtain the neutralino contribution. Because it suffers from less backgrounds, we show that the semileptonic decay channel has a better discovery reach than the fully hadronic decay channel along the compressed line $m_{\tilde{t}}-m_{\tilde{\chi }}\approx m_t$. With 300 ${\text{fb}}^{-1}$, the 13 TeV LHC can discover the stop up to 500 GeV, covering the most natural parameter space region.

   hep-phhep-exJHEP(2016)·19 citations
3. 03*

   Baryogenesis via Particle-Antiparticle Oscillations

   Seyda Ipek🇺🇸 · John March-Russell🇬🇧

   CP violation, which is crucial for producing the baryon asymmetry of the Universe, is enhanced in particle-antiparticle oscillations. We study particle-antiparticle oscillations (of a particle with mass O(100 GeV)) with CP violation in the early Universe in the presence of interactions with O(ab-fb) cross-sections. We show that, if baryon-number-violating interactions exist, a baryon asymmetry can be produced via out-of-equilibrium decays of oscillating particles. As a concrete example we study a $U(1{)}_R$-symmetric, R-parity-violating SUSY model with pseudo-Dirac gauginos, which undergo particle-antiparticle oscillations. Taking bino to be the lightest $U(1{)}_R$-symmetric particle, and assuming it decays via baryon-number-violating interactions, we show that bino-antibino oscillations can produce the baryon asymmetry of the Universe.

   hep-phPRD(2016)·28 citations
4. 04*

   Chiral matrix model of the semi-Quark Gluon Plasma in QCD

   Robert D. Pisarski🇺🇸 · Vladimir V. Skokov🇺🇸

   A chiral matrix model applicable to QCD with 2+1 flavors is developed. This requires adding a SU(3)_L x SU(3)_R x Z(3)_A nonet of scalar fields, with both parities, and coupling these to quarks through a Yukawa coupling, y. Treating the scalar fields in mean field approximation, the effective Lagrangian is computed by integrating out quarks to one loop order. In addition to the usual symmetry breaking term, linear in the current quark mass m_qk, at a nonzero temperature T it is necessary to add a new term, ~ m_qk T^2. The parameters of the gluon part of the matrix model are identical to that for the pure glue theory without quarks. The parameters in the chiral matrix model are fixed by the values, at zero temperature, of the pion decay constant and the masses of the pions, kaons, eta, and eta'. The temperature for the chiral crossover at T_chi = 155 MeV is determined by adjusting the Yukawa coupling y. We find reasonable agreement with the results of numerical simulations on the lattice for the pressure and related quantities. In the chiral limit, besides the divergence in the chiral susceptibility there is also a milder divergence in the susceptibility between the Polyakov loop and the chiral order parameter, with critical exponent beta - 1. We compute derivatives with respect to a quark chemical potential to determine the susceptibilities for baryon number, the chi_2n. Especially sensitive tests are provided by chi_4 - chi_2 and by chi_6, which changes in sign about T_chi. The behavior of the susceptibilities in the chiral matrix model strongly suggests that as the temperature increases from T_chi, that the transition to deconfinement is significantly quicker than indicated by the measurements of the (renormalized) Polyakov loop on the lattice.

   hep-phPRD(2016)·52 citations
5. 05*

   The asymptotic behaviour of parton distributions at small and large $x$

   Richard D. Ball🇬🇧 · Emanuele R. Nocera🇬🇧 · Juan Rojo🇬🇧

   It has been argued from the earliest days of quantum chromodynamics (QCD) that at asymptotically small values of $x$ the parton distribution functions (PDFs) of the proton behave as $x^{\alpha }$, where the values of $\alpha$ can be deduced from Regge theory, while at asymptotically large values of $x$ the PDFs behave as $(1-x{)}^{\beta }$, where the values of $\beta$ can be deduced from the Brodsky-Farrar quark counting rules. We critically examine these claims by extracting the exponents $\alpha$ and $\beta$ from various global fits of parton distributions, analysing their scale dependence, and comparing their values to the naive expectations. We find that for valence distributions both Regge theory and counting rules are confirmed, at least within uncertainties, while for sea quarks and gluons the results are less conclusive. We also compare results from various PDF fits for the structure function ratio $F_2^n/F_2^p$ at large $x$, and caution against unrealistic uncertainty estimates due to overconstrained parametrisations.

   hep-phEPJC(2016)·90 citations
6. 06*

   Dark Gauge Bosons: LHC Signatures of Non-Abelian Kinetic Mixing

   Carlos A. Argüelles🇺🇸 · Xiao-Gang He🇨🇳 · Grigory Ovanesyan🇺🇸 · Tao Peng🇺🇸 · Michael J. Ramsey-Musolf🇺🇸

   We consider non-abelian kinetic mixing between the Standard Model SU(2${)}_L$ and a dark sector U(1${)}^{\prime }$ gauge group associated with the presence of a scalar SU(2${)}_L$ triplet. The magnitude of the resulting dark photon coupling $ϵ$ is determined by the ratio of the triplet vacuum expectation value, constrained to by $\text{lsim}4$ GeV by electroweak precision tests, to the scale $\Lambda$ of the effective theory. The corresponding effective operator Wilson coefficient can be $\mathcal{O}(1)$ while accommodating null results for dark photon searches, allowing for a distinctive LHC dark photon phenomenology. After outlining the possible LHC signatures, we illustrate by recasting current ATLAS dark photon results into the non-abelian mixing context.

   hep-phPLB(2017)·25 citations
7. 07*

   Dynamical Electroweak Symmetry Breaking in the model of electroweak-scale right-handed neutrinos

   P. Q. Hung🇺🇸 · N. N. Le🇻🇳

   We present the Higgs mechanism in the context of the EW-scale ${\nu }_R$ model in which electroweak symmetry is dynamically broken by condensates of mirror quark and right-handed neutrino through the exchange of one fundamental Higgs doublet and one fundamental Higgs triplet, respectively. The formation of these condensates is dynamically investigated by using the Schwinger-Dyson approach. The occurrence of these condensates will give rise to the rich Higgs spectrum. In addition, the VEVs of Higgs fields is also discussed in this dynamical phenomenon.

   hep-phInt.J.Mod.Phys.A(2016)·2 citations
8. 08*

   Holographic Schwinger effect in a confining D3-brane background with chemical potential

   Zi-qiang Zhang🇨🇳 · De-fu Hou🇨🇳 · Yan Wu🇨🇳 · Gang Chen🇨🇳

   Using the AdS/CFT correspondence, we investigate the Schwinger effect in a confining D3-brane background with chemical potential. The potential between a test particle pair on the D3-brane in an external electric field is obtained. The critical field $E_c$ in this case is calculated. Also, we apply numerical method to evaluate the production rate for various cases. The results imply that the presence of chemical potential tends to suppress the pair production effect.

   hep-phAdv.High Energy Phys.(2016)·8 citations
9. 09*

   Higgs exotic decays in general NMSSM with self-interacting dark matter

   Wenyu Wang🇨🇳 · Mengchao Zhang🇨🇳 · Jun Zhao🇨🇳

   Under current LHC and dark matter constraints, the general NMSSM can have self-interacting dark matter to explain the cosmological small structure. In this scenario, the dark matter is the light singlino-like neutralino ($\chi$) which self-interacts through exchanging the light singlet-like scalars ($h_1,a_1$). These light scalars and neutralinos inevitably interact with the 125 GeV SM-like Higgs boson ($h_{SM}$), which cause the Higgs exotic decays $h_{SM}\to h_1{h}_1,a_1{a}_1,\chi \chi$. We first demonstrate the parameter space required by the explanation of the cosmological small structure and then display the Higgs exotic decays. We find that in such a parameter space the Higgs exotic decays can have branching ratios of a few percent, which should be accessible in the future $e^{+}{e}^{-}$ colliders.

   hep-phastro-ph.COInt.J.Mod.Phys.A(2018)·12 citations
10. 10*

    Mechanisms of the isospin-breaking decay $f_1(1285)\to f_0(980){\pi }^0\to {\pi }^{+}{\pi }^{-}{\pi }^0$

    N.N. Achasov🇷🇺 · A.A. Kozhevnikov🇷🇺 · G.N. Shestakov🇷🇺

    Estimated are the contributions of the following mechanisms responsible for the decay $f_1(1285)\to f_0(980){\pi }^0\to {\pi }^{+}{\pi }^{-}{\pi }^0$: 1) the contribution of the $a_0^0(980)-f_0(980)$ mixing, $f_1(1285)\to a_0(980){\pi }^0\to (K^{+}{K}^{-}+K^0{\bar{K}}^0){\pi }^0\to f_0(980){\pi }^0\to {\pi }^{+}{\pi }^{-}{\pi }^0$, 2) the contribution of the transition $f_1(1285)\to (K^{+}{K}^{-}+K^0{\bar{K}}^0){\pi }^0\to f_0(980){\pi }^0\to {\pi }^{+}{\pi }^{-}{\pi }^0$, arising due to the pointlike decay $f_1(1285)\to K\bar{K}{\pi }^0$, 3) the contribution of the transition $f_1(1285)\to (K^{\ast }\bar{K}+{\bar{K}}^{\ast }K)\to (K^{+}{K}^{-}+K^0{\bar{K}}^0){\pi }^0\to f_0(980){\pi }^0\to {\pi }^{+}{\pi }^{-}{\pi }^0$, where $K^{\ast }=K^{\ast }(892)$, and 4) the contribution of the transition $f_1(1285)\to (K_0^{\ast }\bar{K}+{\bar{K}}_0^{\ast }K)\to (K^{+}{K}^{-}+K^0{\bar{K}}^0){\pi }^0\to f_0(980)\to {\pi }^{+}{\pi }^{-}{\pi }^0$, where $K_0^{\ast }=K_0^{\ast }(800)$ (or $\kappa$) and $K_0^{\ast }(1430)$. These mechanisms break the conservation of the isospin due to the nonzero mass difference of the $K^{+}$ and $K^0$ mesons. They result in the appearance of the narrow resonance structure in the ${\pi }^{+}{\pi }^{-}$ mass spectrum in the region of the $K\bar{K}$ thresholds, with the width $\approx 2m_{K^0}-2m_{K^{+}}\approx 8$ MeV. The observation of such a structure in experiment is the direct indication on the $K\bar{K}$ loop mechanism of the breaking of the isotopic invariance. We point out that existing data should be more precise, and it is difficult to explain them using the single specific mechanism from those listed above. Taking the decay $f_1(1285)\to f_0(980){\pi }^0\to {\pi }^{+}{\pi }^{-}{\pi }^0$ as the example, we discuss the general approach to the description of the $K\bar{K}$ loop mechanism of the breaking of isotopic invariance.

    hep-phhep-exnucl-thPRD(2016)·22 citations
11. 11*

    Arguing on entropic and enthalpic first-order phase transitions in strongly interacting matter

    Falk Wunderlich🇩🇪 · Roman Yaresko🇩🇪 · Burkhard Kampfer🇩🇪

    The pattern of isentropes in the vicinity of a first-order phase transition is proposed as a key for a sub-classification. While the confinement--deconfinement transition, conjectured to set in beyond a critical end point in the QCD phase diagram, is often related to an entropic transition and the apparently settled gas-liquid transition in nuclear matter is an enthalphic transition, the conceivable local isentropes w.r.t.\ "incoming" or "outgoing" serve as another useful guide for discussing possible implications, both in the presumed hydrodynamical expansion stage of heavy-ion collisions and the core-collapse of supernova explosions. Examples, such as the quark-meson model and two-phase models, are shown to distinguish concisely the different transitions.

    hep-phJ.Mod.Phys.(2016)·7 citations
12. 12*

    Pair production by Schwinger and Breit-Wheeler processes in bi-frequent fields

    A. Otto · T. Nousch · D. Seipt B. Kämpfer · D. Blaschke · A. D. Panferov · S. A. Smolyansky · A. I. Titov

    Counter-propagating and suitably polarized light (laser) beams can provide conditions for pair production. Here, we consider in more detail the following two situations: (i) In the homogeneity regions of anti-nodes of linearly polarized ultra-high intensity laser beams, the Schwinger process is dynamically assisted by a second high-frequency field, e.g. by a XFEL beam. (ii) A high-energy probe photon beam colliding with a superposition of co-propagating intense laser and XFEL beams gives rise to the laser assisted Breit-Wheeler process. Prospects of such bi-frequent field constellations with respect to the feasibility of conversion of light into matter are discussed.

    hep-phphysics.plasm-phJ.Plasma Phys.(2016)·22 citations
13. 13*

    Laser assisted Breit-Wheeler and Schwinger processes

    T. Nousch🇩🇪 · A. Otto🇩🇪 · D. Seipt🇩🇪 · B. Kämpfer🇩🇪 · A. I. Titov🇷🇺 · D. Blaschke🇷🇺 · A. D. Panferov🇷🇺 · S. A. Smolyansky🇷🇺

    The assistance of an intense optical laser pulse on electron-positron pair production by the Breit-Wheeler and Schwinger processes in XFEL fields is analyzed. The impact of a laser beam on high-energy photon collisions with XFEL photons consists in a phase space redistribution of the pairs emerging in the Breit-Wheeler sub-process. We provide numerical examples of the differential cross section for parameters related to the European XFEL. Analogously, the Schwinger type pair production in pulsed fields with oscillating components referring to a superposition of optical laser and XFEL frequencies is evaluated. The residual phase space distribution of created pairs is sensitive to the pulse shape and may differ significantly from transiently achieved mode occupations.

    hep-phphysics.atom-phFIAS Interdisc.Sci.Ser.(2017)·1 citation
14. 14*

    Probing the non-unitarity of the leptonic mixing matrix at the CEPC

    Stefan Antusch🇨🇭 · Oliver Fischer🇨🇭

    The non-unitarity of the leptonic mixing matrix is a generic signal of new physics aiming at the generation of the observed neutrino masses. We discuss the Minimal Unitarity Violation (MUV) scheme, an effective field theory framework which represents the class of extensions of the Standard Model (SM) by heavy neutral leptons, and discuss the present bounds on the non-unitarity parameters as well as estimates for the sensitivity of the Circular Electron Positron Collider (CEPC), based on the performance parameters from the preCDR.

    hep-phInt.J.Mod.Phys.A(2016)·32 citations
15. 15*

    Testable SUSY spectra from GUTs at a 100 TeV pp collider

    Stefan Antusch🇨🇭 · Constantin Sluka🇨🇭

    Grand Unified Theories (GUTs) are attractive candidates for more fundamental elementary particle theories. They can not only unify the Standard Model (SM) interactions but also different types of SM fermions, in particular quarks and leptons, in joint representations of the GUT gauge group. We discuss how comparing predictive supersymmetric GUT models with the experimental results for quark and charged lepton masses leads to constraints on the SUSY spectrum. We show an example from a recent analysis where the resulting superpartner masses where found just beyond the reach of LHC run 1, but fully within the reach of a 100 TeV pp collider.

    hep-phInt.J.Mod.Phys.A(2016)·9 citations
16. 16*

    Single inclusive forward hadron production at next-to-leading order

    B. Ducloué🇫🇮 · T. Lappi🇫🇮 · Y. Zhu🇫🇮

    We discuss single inclusive hadron production from a high energy quark scattering off a strong target color field in the Color Glass Condensate formalism. Recent calculations of this process at the next-to-leading order accuracy have led to negative cross sections at large transverse momenta. We identify the origin of this problem as an oversubtraction of the rapidity divergence into the Balitsky-Kovchegov evolution equation for the target. We propose a new way to implement the kinematical restriction on the emitted gluons to overcome this difficulty.

    hep-phnucl-thPRD(2016)·70 citations
17. 17*

    Higgs bosons: discovered and hidden, in extended Supersymmetric Standard Models at the LHC

    Priyotosh Bandyopadhyay🇮🇹 · Claudio Coriano🇮🇹 · Antonio Costantini🇮🇹

    We investigate an extension of the Minimal Supersymmetric Standard Model (MSSM) containing a $SU(2)$ Higgs triplet of zero hypercharge and a gauge singlet. We focus on a scenario of this model which allows a light pseudoscalar and/or a scalar below $100$ GeV in the spectrum, consistent with the most recent data from the LHC and the earlier data from the LEP experiments. We analyze the exotic decay of the discovered Higgs $(h_{125})$ into two light (hidden) Higgs bosons present in the extension. The latter are allowed by the uncertainties in the Higgs decay $h_{125}\to W{W}^{\ast }$, $h_{125}\to Z{Z}^{\ast }$ and $h_{125}\to \gamma \gamma$. We have searched for such light Higgs bosons in the $2b+2\tau$, $\ge 3\tau$, $2b+2\mu$ and $2\tau +2\mu$ final states at the LHC with 13 and 14 TeV. A region of such parameter space can be explored with an integrated luminosity of 25 fb${}^{-1}$ at the LHC.

    hep-phPoS(2016)·0 citations
18. 18*

    Numerical multi-loop calculations: tools and applications

    S.Borowka🇨🇭 · G.Heinrich🇩🇪 · S.Jahn🇩🇪 · S.P.Jones🇩🇪 · M.Kerner🇩🇪 · J.Schlenk🇩🇪 · T.Zirke🇩🇪

    We report on the development of tools to calculate loop integrals and amplitudes beyond one loop. In particular, we review new features of the program SecDec which can be used for the numerical evaluation of parametric integrals like multi-loop integrals.

    hep-phJ.Phys.Conf.Ser.(2016)·7 citations
19. 19*

    An effective field theory approach to hybrids

    Matthias Berwein🇩🇪

    Heavy quarkonium hybrids are studied in an effective field theory framework. Coupled and uncoupled Schrödinger equations are obtained for different quantum numbers of the hybrid states. The results are discussed and compared to other approaches.

    hep-phJ.Phys.Conf.Ser.(2016)·0 citations
20. 20*

    The end of WHAT nucleon-spin crisis?

    Elliot Leader🇬🇧

    Povh and Walcher have written a paper entitled "The end of the nucleon-spin crisis" [arXiv:1603.05884]. But there is no such crisis. What appeared to be a spin crisis in the parton model, 28 years ago, was a consequence of a misinterpretation of the results of the famous European Muon Collaboration experiment on polarized deep inelastic scattering. It would thus seem that Povh and Walcher have invoked a somewhat dubious argument based on hadronic fluctuations of the photon in order to resolve a non-existent problem.

    hep-phhep-ex9 citations
21. 21*

    Prospects for Future Collider Physics

    John Ellis🇬🇧

    One item on the agenda of future colliders is certain to be the Higgs boson. What is it trying to tell us? The primary objective of any future collider must surely be to identify physics beyond the Standard Model, and supersymmetry is one of the most studied options. it Is supersymmetry waiting for us and, if so, can LHC Run 2 find it? The big surprise from the initial 13-TeV LHC data has been the appearance of a possible signal for a new boson X with a mass ~750 GeV. What are the prospects for future colliders if the X(750) exists? One of the most intriguing possibilities in electroweak physics would be the discovery of non-perturbative phenomena. What are the prospects for observing sphalerons at the LHC or a future collider?

    hep-phInt.J.Mod.Phys.A(2016)·3 citations
22. 22*

    Initial State Quantum Fluctuations in the Little Bang

    Francois Gelis🇫🇷 · Bjoern Schenke🇺🇸

    We review recent developments in the ab-initio theoretical description of the initial state in heavy-ion collisions. We emphasize the importance of fluctuations, both for the phenomenological description of experimental data from the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC), and the theoretical understanding of the non-equilibrium early time dynamics and thermalization of the medium.

    hep-phnucl-thAnn.Rev.Nucl.Part.Sci.(2016)·30 citations
23. 23*

    Universal Bounds on Charged States in 2d CFT and 3d Gravity

    Nathan Benjamin🇺🇸 · Ethan Dyer🇺🇸 · A. Liam Fitzpatrick🇺🇸 · Shamit Kachru🇺🇸

    We derive an explicit bound on the dimension of the lightest charged state in two dimensional conformal field theories with a global abelian symmetry. We find that the bound scales with $c$ and provide examples that parametrically saturate this bound. We also prove than any such theory must contain a state with charge-to-mass ratio above a minimal lower bound. We comment on the implications for charged states in three dimensional theories of gravity.

    ↳ hep-thhep-phJHEP(2016)·100 citations
24. 24*

    A review of indirect searches for particle dark matter

    Jennifer M. Gaskins🇺🇸

    The indirect detection of dark matter annihilation and decay using observations of photons, charged cosmic rays, and neutrinos offers a promising means of identifying the particle nature of this elusive component of the universe. The last decade has seen substantial advances in observational data sets, complemented by new insights from numerical simulations, which together have enabled for the first time strong constraints on dark matter particle models, and have revealed several intriguing hints of possible signals. This review provides an introduction to indirect detection methods and an overview of recent results in the field.

    ↳ astro-ph.HEastro-ph.COhep-phContemp.Phys.(2016)·482 citations
25. 25*

    Correlations and fluctuations of pions at the LHC

    Viktor V. Begun🇵🇱

    The intriguing possibility of Bose-Einstein condensation of pions at the LHC is examined with the use of higher order moments of the multiplicity distribution. The scaled variance, skewness and kurtosis are calculated for the pion system. The obtained results show that the normalized kurtosis has a significant increase for the case of the pion condensation.

    ↳ nucl-thhep-exhep-phnucl-exActa Phys.Polon.Supp.(2016)·1 citation
26. 26*

    Anisotropies in the gravitational wave background as a probe of the cosmic string network

    Sachiko Kuroyanagi🇯🇵 · Keitaro Takahashi🇯🇵 · Naoyuki Yonemaru🇯🇵 · Hiroki Kumamoto🇯🇵

    Pulsar timing arrays are one of the powerful tools to test the existence of cosmic strings through searching for the gravitational wave background. The amplitude of the background connects to information on cosmic strings such as the tension and string network properties. In addition, one may be able to extract more information on properties of cosmic strings by measuring anisotropies in the gravitational wave (GW) background. In this paper, we provide estimates of the level of anisotropy expected in the GW background generated by cusps on cosmic strings. We find that the anisotropy level strongly depends on the initial loop size $\alpha$, and thus we may be able to put constraint on $\alpha$ by measuring the anisotropy of the GW background. We also find that certain regions of the parameter space can be probed by shifting the observation frequency of GWs.

    ↳ astro-ph.COgr-qchep-phhep-thPRD(2017)·33 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.