Mon·Jan 9, 2017Monday·January 9, 2017

1. 01*

   Naturalness of asymptotically safe Higgs

   Giulio Maria Pelaggi🇮🇹 · Francesco Sannino🇩🇰 · Alessandro Strumia🇨🇭 · Elena Vigiani🇮🇹

   We extend the list of theories featuring a rigorous interacting ultraviolet fixed point by constructing the first theory featuring a Higgs-like scalar with gauge, Yukawa and quartic interactions. We show that the theory enters a perturbative asymptotically safe regime at energies above a physical scale $\Lambda$. We determine the salient properties of the theory and use it as a concrete example to test whether scalars masses unavoidably receive quantum correction of order $\Lambda$. Having at our dispose a calculable model allowing us to precisely relate the IR and UV of the theory we demonstrate that the scalars can be lighter than $\Lambda$. Although we do not have an answer to whether the Standard Model hypercharge coupling growth towards a Landau pole at around $\Lambda \sim 10^{40}$ GeV can be tamed by non-perturbative asymptotic safety, our results indicate that such a possibility is worth exploring. In fact, if successful, it might also offer an explanation for the unbearable lightness of the Higgs.

   hep-phFront.in Phys.(2017)·45 citations
2. 02*

   Combined threshold and transverse momentum resummation for inclusive observables

   Claudio Muselli🇮🇹 · Stefano Forte🇮🇹 · Giovanni Ridolfi🇮🇹

   We present a combined resummation for the transverse momentum distribution of a colorless final state in perturbative QCD, expressed as a function of transverse momentum pt and the scaling variable x. Its expression satisfies three requirements: it reduces to standard transverse momentum resummation to any desired logarithmic order in the limit pt-> 0 for fixed x, up to power suppressed corrections in pt; it reduces to threshold resummation to any desired logarithmic order in the limit x-> 1 for fixed pt, up to power suppressed correction in 1-x; upon integration over transverse momentum it reproduces the resummation of the total cross cross at any given logarithmic order in the threshold x->1 limit. Its main ingredient, and our main new result, is a modified form of transverse momentum resummation, which leads to threshold resummation upon integration over pt, and for which we provide a simple closed-form analytic expression in Fourier-Mellin (b,N) space. We give explicit coefficients up to NNLL order for the specific case of Higgs production in gluon fusion in the effective field theory limit. Our result allows for a systematic improvement of the transverse momentum distribution through threshold resummation which holds for all pt, and elucidates the relation between transverse momentum resummation and threshold resummation at the inclusive level, specifically by providing within perturbative QCD a simple derivation of the main consequence of the so-called collinear anomaly of SCET.

   hep-phJHEP(2017)·53 citations
3. 03*

   The hidden-charm multiquark states

   Hua-Xing Chen🇨🇳 · Wei Chen🇨🇦 · Jun He🇨🇳 · Xiang Liu🇨🇳 · Shi-Lin Zhu🇨🇳

   Since 2003 many charmonium-like states were observed experimentally. Especially those charged charmonium-like $Z_c$ states and bottomonium-like $Z_b$ states cannot be accommodated within the naive quark model, which are good candidates of either the hidden-charm tetraquark states or molecules composed of a pair of charmed mesons. In 2015, the LHCb Collaboration discovered two hidden-charm pentaquark states, which are also beyond the quark model. In this talk, we review the current experimental progress and investigate various theoretical interpretations of these candidates of the multiquark states. We list the puzzles and theoretical challenges of these models when confronted with the experimental data. We also discuss possible future measurements which may distinguish the theoretical schemes on the underlying structures of the hidden-charm multiquark states.

   hep-phhep-exhep-latnucl-thPoS(2017)·1 citation
4. 04*

   Basics of thermal field theory -- a tutorial on perturbative computations

   Mikko Laine🇨🇭 · Aleksi Vuorinen🇫🇮

   These lecture notes, suitable for a two-semester introductory course or self-study, offer an elementary and self-contained exposition of the basic tools and concepts that are encountered in practical computations in perturbative thermal field theory. Selected applications to heavy ion collision physics and cosmology are outlined in the last chapter.

   hep-phLect.Notes Phys.(2016)·403 citations
5. 05*

   $B\to \pi \pi$ Form Factors from Light-Cone Sum Rules with $B$-meson Distribution Amplitudes

   Shan Cheng🇩🇪 · Alexander Khodjamirian🇩🇪 · Javier Virto🇨🇭

   We study $B\to \pi \pi$ form factors using QCD light-cone sum rules with $B$-meson distribution amplitudes. These form factors describe the semileptonic decay $B\to \pi \pi \ell {\bar{\nu }}_{\ell }$, and constitute an essential input in $B\to \pi \pi {\ell }^{+}{\ell }^{-}$ and $B\to \pi \pi \pi$ decays. We employ the correlation functions where a dipion isospin-one state is interpolated by the vector light-quark current. We obtain sum rules where convolutions of the $P$-wave ${\bar{B}}^0\to {\pi }^{+}{\pi }^0$ form factors with the time-like pion vector form factor are related to universal $B$-meson distribution amplitudes. These sum rules are valid in the kinematic regime where the dipion state has a large energy and a low invariant mass, and reproduce analytically the known light-cone sum rules for $B\to \rho$ form factors in the limit of $\rho$-dominance with zero width, thus providing a systematics for so-far-unaccounted corrections to $B\to \rho$ transitions. Using data for the pion vector form factor, we estimate finite width-effects and the contribution of excited $\rho$-resonances to the $B\to \pi \pi$ form factors. We find that these contributions amount up to $\sim 20\%$ in the small dipion mass region where they can be effectively regarded as a nonresonant ($P$-wave) background to the $B\to \rho$ transition.

   hep-phhep-exJHEP(2017)·66 citations
6. 06*

   Exploring the squark flavour structure of the MSSM

   Karen De Causmaecker🇧🇪 · Benjamin Fuks🇫🇷 · Björn Herrmann🇫🇷 · Farvah Mahmoudi🇫🇷 · Ben O'Leary🇩🇪 · Werner Porod🇩🇪 · Sezen Sekmen🇰🇷 · Nadja Strobbe🇺🇸

   We present an extensive study of the MSSM parameter space allowing for general generation mixing in the squark sector. Employing an MCMC algorithm, we establish the parameter ranges which are allowed with respect to various experimental and theoretical constraints. Based on this analysis, we propose benchmark scenarios for future studies. Moreover, we discuss aspects of signatures at the LHC.

   hep-phPoS(2016)·0 citations
7. 07*

   Toward an Effective Field Theory Approach to Reheating

   Ogan Ozsoy🇺🇸 · John T. Giblin Jr.🇺🇸 · Eva Nesbit🇺🇸 · Gizem Sengor🇺🇸 · Scott Watson🇺🇸

   We investigate whether Effective Field Theory (EFT) approaches, which have been useful in examining inflation and dark energy, can also be used to establish a systematic approach to inflationary reheating. We consider two methods. First, we extend Weinberg's background EFT to the end of inflation and reheating. We establish when parametric resonance and decay of the inflaton occurs, but also find intrinsic theoretical limitations, which make it difficult to capture some reheating models. This motivates us to next consider Cheung, et. al.'s EFT approach, which instead focuses on perturbations and the symmetry breaking induced by the cosmological background. Adapting the latter approach to reheating implies some new and important differences compared to the EFT of Inflation. In particular, there are new hierarchical scales, and we must account for inflaton oscillations during reheating, which lead to discrete symmetry breaking. Guided by the fundamental symmetries, we construct the EFT of reheating, and as an example of its usefulness we establish a new class of reheating models and the corresponding predictions for gravity wave observations. In this paper we primarily focus on the first stages of preheating. We conclude by discussing challenges for the approach and future directions. This paper builds on ideas first proposed in the note arXiv:1507.06651.

   ↳ hep-thastro-ph.COhep-phPRD(2017)·27 citations
8. 08*

   Collisions of Dark Matter Axion Stars with Astrophysical Sources

   Joshua Eby🇺🇸 · Madelyn Leembruggen🇺🇸 · Joseph Leeney🇺🇸 · Peter Suranyi🇺🇸 · L.C.R. Wijewardhana🇺🇸

   If QCD axions form a large fraction of the total mass of dark matter, then axion stars could be very abundant in galaxies. As a result, collisions with each other, and with other astrophysical bodies, can occur. We calculate the rate and analyze the consequences of three classes of collisions, those occurring between a dilute axion star and: another dilute axion star, an ordinary star, or a neutron star. In all cases we attempt to quantify the most important astrophysical uncertainties; we also pay particular attention to scenarios in which collisions lead to collapse of otherwise stable axion stars, and possible subsequent decay through number changing interactions. Collisions between two axion stars can occur with a high total rate, but the low relative velocity required for collapse to occur leads to a very low total rate of collapses. On the other hand, collisions between an axion star and an ordinary star have a large rate, ${\Gamma }_{\odot }\sim 3000$ collisions/year/galaxy, and for sufficiently heavy axion stars, it is plausible that most or all such collisions lead to collapse. We identify in this case a parameter space which has a stable region and a region in which collision triggers collapse, which depend on the axion number ($N$) in the axion star, and a ratio of mass to radius cubed characterizing the ordinary star ($M_s/R_s^3$). Finally, we revisit the calculation of collision rates between axion stars and neutron stars, improving on previous estimates by taking cylindrical symmetry of the neutron star distribution into account. Collapse and subsequent decay through collision processes, if occurring with a significant rate, can affect dark matter phenomenology and the axion star mass distribution.

   ↳ astro-ph.COhep-phJHEP(2017)·52 citations
9. 09*

   Quark orbital dynamics in the proton from Lattice QCD -- from Ji to Jaffe-Manohar orbital angular momentum

   M. Engelhardt🇺🇸

   Given a Wigner distribution simultaneously characterizing quark transverse positions and momenta in a proton, one can directly evaluate their cross-product, i.e., quark orbital angular momentum. The aforementioned distribution can be obtained by generalizing the proton matrix elements of quark bilocal operators which define transverse momentum-dependent parton distributions (TMDs); the transverse momentum information is supplemented with transverse position information by introducing an additional nonzero momentum transfer. A gauge connection between the quarks must be specified in the quark bilocal operators; the staple-shaped gauge link path used in TMD calculations yields the Jaffe-Manohar definition of orbital angular momentum, whereas a straight path yields the Ji definition. An exploratory lattice calculation, performed at the pion mass m_pi = 518 MeV, is presented which quasi-continuously interpolates between the two definitions and demonstrates that their difference can be clearly resolved. The resulting Ji orbital angular momentum is confronted with traditional evaluations based on Ji's sum rule. Jaffe-Manohar orbital angular momentum is enhanced in magnitude compared to its Ji counterpart.

   ↳ hep-lathep-phPRD(2017)·62 citations
10. 10*

    Effects on the CMB from Compactification Before Inflation

    Eleni-Alexandra Kontou🇺🇸 · Jose J. Blanco-Pillado🇪🇸 · Mark P. Hertzberg🇺🇸 · Ali Masoumi🇺🇸

    Many theories beyond the Standard Model include extra dimensions, though these have yet to be directly observed. In this work we consider the possibility of a compactification mechanism which both allows extra dimensions and is compatible with current observations. This compactification is predicted to leave a signature on the CMB by altering the amplitude of the low l multipoles, dependent on the amount of inflation. Recently discovered CMB anomalies at low multipoles may be evidence for this. In our model we assume the spacetime is the product of a four-dimensional spacetime and flat extra dimensions. Before the compactification, both the four-dimensional space- time and the extra dimensions can either be expanding or contracting independently. Taking into account physical constraints, we explore the observational consequences and the plausibility of these different models.

    ↳ hep-thastro-ph.COgr-qchep-phJCAP(2017)·5 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.