Mon·May 18, 2020Monday·May 18, 2020

1. 01*

   Signals with six bottom quarks for charged and neutral Higgs bosons

   Radovan Dermisek🇺🇸 · Enrico Lunghi🇺🇸 · Navin McGinnis🇺🇸 · Seodong Shin🇰🇷

   In extensions of two Higgs doublet models with vectorlike quarks, the decays of vectorlike quarks may easily be dominated by cascade decays through charged or neutral Higgs bosons leading to signatures with 6 top or bottom quarks. Since top quark decays also contain bottom quarks, a common signature for many possible decay chains is 6 bottom quarks in the final state. We present a search strategy focusing on this final state and find the mass ranges of vectorlike quarks and Higgs bosons that can be explored at the Large Hadron Collider. Among other results, the sensitivity to the charged and neutral Higgs bosons, extending to about 2 TeV, stands out when compared to models without vectorlike matter.

   hep-phhep-exJHEP(2020)·30 citations
2. 02*

   Decay of a bound muon into a bound electron

   M. Jamil Aslam🇵🇰 · Andrzej Czarnecki🇨🇦 · Guangpeng Zhang🇨🇦 · Anna Morozova🇨🇦

   When a muon bound in an atom decays, there is a small probability that the daughter electron remains bound. That probability is evaluated. Surprisingly, a significant part of the rate is contributed by the negative energy component of the wave function, neglected in a previous study. A simple integral representation of the rate is presented. In the limit of close muon and electron masses, an analytic formula is derived.

   hep-phPRD(2020)·5 citations
3. 03*

   Helicity at Small $x$: Oscillations Generated by Bringing Back the Quarks

   Yuri V. Kovchegov🇺🇸 · Yossathorn Tawabutr🇺🇸

   We construct a numerical solution of the recently-derived large-$N_c\&N_f$ small-$x$ helicity evolution equations with the aim to establish the small-$x$ asymptotics of the quark helicity distribution beyond the large-$N_c$ limit explored previously in the same framework. (Here $N_c$ and $N_f$ are the numbers of quark colors and flavors.) While the large-$N_c$ helicity evolution involves gluons only, the large-$N_c\&N_f$ evolution includes contributions from quarks as well. We find that adding quarks to the evolution makes quark helicity distribution oscillate as a function of $x$. Our numerical results in the large-$N_c\&N_f$ limit lead to the $x$-dependence of the flavor-singlet quark helicity distribution which is well-approximated by \begin{align} \Delta \Sigma (x, Q^2)\bigg|_{\mbox{large-}N_c \& N_f} \sim \left( \frac{1}{x} \right)^{\alpha_h^q} \, \cos \left[ \omega_q \, \ln \left( \frac{1}{x} \right) + \varphi_q \right]. \end{align} The power ${\alpha }_h^q$ exhibits a weak $N_f$-dependence, and, for all $N_f$ values considered, remains very close to ${\alpha }_h^q(N_f=0)=(4/\sqrt{3})\sqrt{{\alpha }_s{N}_c/(2\pi )}$ obtained earlier in the large-$N_c$ limit. The novel oscillation frequency ${\omega }_q$ and phase shift ${\phi }_q$ depend more strongly on the number of flavors $N_f$ (with ${\omega }_q=0$ in the pure-glue large-$N_c$ limit). The typical period of oscillations for $\Delta \Sigma$ is rather long, spanning many units of rapidity. We speculate whether the oscillations we find are related to the sign variation with $x$ seen in the strange quark helicity distribution extracted from the data.

   hep-phhep-exnucl-exnucl-thJHEP(2020)·57 citations
4. 04*

   NLO QCD corrections to $B_c$-pair production in photon-photon collision

   Zi-Qiang Chen🇨🇳 · Hao Yang🇨🇳 · Cong-Feng Qiao🇨🇳

   The $B_c$ meson pair, including pairs of both pseudoscalar states and vector states, productions in high energy photon-photon interaction are investigated at the next-to-leading order (NLO) accuracy in the nonrelativistic quantum chromodynamics (NRQCD) factorization formalism. The corresponding cross sections at the future $e^{+}{e}^{-}$ colliders with $\sqrt{s}=250$ GeV and $500$ GeV are evaluated. Numerical result indicates that the inclusion of the NLO corrections shall greatly suppress the scale dependence and enhance the prediction reliability. In addition to the phenomenological meaning, the NLO QCD calculation of this process subjects to certain technical issues, which are elucidated in details and might be applicable to other relevant investigations.

   hep-phPRD(2020)·14 citations
5. 05*

   New Constraints on Supersymmetry Using Neutrino Telescopes

   Stephan Meighen-Berger🇩🇪 · Matteo Agostini🇬🇧 · Alejandro Ibarra🇩🇪 · Kai Krings🇩🇪 · Hans Niederhausen🇩🇪 · Andreas Rappelt🇩🇪 · Elisa Resconi🇩🇪 · Andrea Turcati🇩🇪

   We demonstrate that megaton-mass neutrino telescopes are able to observe the signal from long-lived particles beyond the Standard Model, in particular the stau, the supersymmetric partner of the tau lepton. Its signature is an excess of charged particle tracks with horizontal arrival directions and energy deposits between 0.1 and 1 TeV inside the detector. We exploit this previously-overlooked signature to search for stau particles in the publicly available IceCube data. The data shows no evidence of physics beyond the Standard Model. We derive a new lower limit on the stau mass of $320$ GeV (95\% C.L.) and estimate that this new approach, when applied to the full data set available to the IceCube collaboration, will reach world-leading sensitivity to the stau mass ($m_{\tilde{\tau }}=450\mathrm{GeV}$).

   hep-phhep-exPLB(2020)·13 citations
6. 06*

   Large $N_f$ for multiple representations

   Giacomo Cacciapaglia🇫🇷 · Shahram Vatani🇫🇷

   We present an extension of the large $N_f$ formalism that allows to study cases with multiple fermion representations. The pole structure in the beta function is traced back to the intrinsic non-abelian nature of the gauge group, independently on the fermion representation. This result validates the conjectured existence of an interactive UV fixed point for non-abelian gauge theories with large fermion multiplicity. Finally, we apply our results to chiral gauge theories and to extended Grand Unified Theories.

   hep-phEPJC(2021)·3 citations
7. 07*

   Tagging boosted hadronic objects with dynamical grooming

   Yacine Mehtar-Tani🇺🇸 · Alba Soto-Ontoso🇺🇸 · Konrad Tywoniuk🇳🇴

   We evaluate the phenomenological applicability of the dynamical grooming technique, introduced in [1], to boosted W and top tagging at LHC conditions. An extension of our method intended for multi-prong decays with an internal mass scale, such as the top quark decay, is presented. First, we tackle the reconstruction of the mass distribution of W and top jets quantifying the smearing due to pileup. When compared to state-of-the-art grooming algorithms like SoftDrop and its recursive version, dynamical grooming shows an enhanced resilience to background fluctuations. In addition, we asses the discriminating power of dynamical grooming to distinguish W (top) jets from QCD ones by performing a two-step analysis: introduce a cut on the groomed mass around the W (top) mass peak followed by a restriction on the N-subjettinnes ratio ${\tau }_{21}$ (${\tau }_{32}$). For W jets, the out-of-the-box version of dynamical grooming, free of ad-hoc parameters, results into a comparable performance to SoftDrop. Regarding the top tagger efficiency, 3-prong dynamical grooming, in spite of its simplicity, presents better performance than SoftDrop and similar results to Recursive SoftDrop.

   hep-phhep-exnucl-exnucl-thPRD(2020)·14 citations
8. 08*

   Analytical description of CP violation in oscillations of atmospheric neutrinos traversing the Earth

   Ara Ioannisian🇦🇲 · Stefan Pokorski🇵🇱 · Janusz Rosiek🇵🇱 · Michal Ryczkowski🇵🇱

   Flavour oscillations of sub-GeV atmospheric neutrinos and antineutrinos, traversing different distances inside the Earth, are a promising source of information on the leptonic CP phase $\delta$. In that energy range, the oscillations are very fast, far beyond the resolution of modern neutrino detectors. However, the necessary averaging over the experimentally typical energy and azimuthal angle bins does not wash out the CP violation effects. In this paper we derive very accurate analytic compact expressions for the averaged oscillations probabilities. Assuming spherically symmetric Earth, the averaged oscillation probabilities are described in terms of two analytically calculable effective parameters. Based on those expressions, we estimate maximal magnitude of CP-violation effects in such measurements and propose optimal observables best suited to determine the value of the CP phase in the PMNS mixing matrix.

   hep-phJHEP(2020)·6 citations
9. 09*

   More on the infrared renormalon in $SU(N)$ QCD(adj.) on ${\mathbb{R}}^3\times S^1$

   Masahiro Ashie🇯🇵 · Okuto Morikawa🇯🇵 · Hiroshi Suzuki🇯🇵 · Hiromasa Takaura🇯🇵

   We present additional observations to previous studies on the infrared (IR) renormalon in $SU(N)$ QCD(adj.), the $SU(N)$ gauge theory with $n_W$-flavor adjoint Weyl fermions on~${\mathbb{R}}^3\times S^1$ with the ${\mathbb{Z}}_N$ twisted boundary condition. First, we show that, for arbitrary finite~$N$, a logarithmic factor in the vacuum polarization of the "photon" (the gauge boson associated with the Cartan generators of~$SU(N)$) disappears under the $S^1$~compactification. Since the IR renormalon is attributed to the presence of this logarithmic factor, it is concluded that there is no IR renormalon in this system with finite~$N$. This result generalizes the observation made by Anber and~Sulejmanpasic [J. High Energy Phys.\ \textbf{1501}, 139 (2015)] for $N=2$ and~$3$ to arbitrary finite~$N$. Next, we point out that, although renormalon ambiguities do not appear through the Borel procedure in this system, an ambiguity appears in an alternative resummation procedure in which a resummed quantity is given by a momentum integration where the inverse of the vacuum polarization is included as the integrand. Such an ambiguity is caused by a simple zero at non-zero momentum of the vacuum polarization. Under the decompactification~$R\to \infty$, where $R$ is the radius of the $S^1$, this ambiguity in the momentum integration smoothly reduces to the IR renormalon ambiguity in~${\mathbb{R}}^4$. We term this ambiguity in the momentum integration "renormalon precursor". The emergence of the IR renormalon ambiguity in~${\mathbb{R}}^4$ under the decompactification can be naturally understood with this notion.

   ↳ hep-thhep-lathep-phPTEP(2020)·6 citations
10. 10*

    Subleading contributions to the nuclear scalar isoscalar currents

    Hermann Krebs🇩🇪 · Evgeny Epelbaum🇩🇪 · Ulf-G. Meißner🇩🇪

    We extend our recent analyses of the nuclear vector, axial-vector and pseudoscalar currents and derive the leading one-loop corrections to the two-nucleon scalar current operator in the framework of chiral effective field theory using the method of unitary transformation. We also show that the scalar current operators at zero momentum transfer are directly related to the quark mass dependence of the nuclear forces.

    ↳ nucl-thhep-phEPJA(2020)·15 citations
11. 11*

    Lowering tensor-to-scalar ratio by pre-inflationary dynamics

    Suratna Das🇮🇳

    Pre-inflationary dynamics is known to have left observable imprints via the varied dynamics of the inflaton and the graviton fields during those epochs. It is highlighted here that other particle degrees of freedom, too, are capable of leaving their imprints on primordial observables if they transfer their entropies upon annihilation after becoming non-relativistic during a pre-inflationary epoch. Such annihilations of other particles would result in lowering of the tensor-to-scalar ratio at the pivot scale (and at length scales larger to that) which would help bring those potentials back in accordance with current observations which are otherwise disfavoured for yielding large tensor-to-scalar ratios at present.

    ↳ astro-ph.COgr-qchep-phPRD(2020)·2 citations
12. 12*

    Energy distribution and equation of state of the early Universe: matching the end of inflation and the onset of radiation domination

    Stefan Antusch🇨🇭 · Daniel G. Figueroa🇪🇸 · Kenneth Marschall🇨🇭 · Francisco Torrenti🇨🇭

    We study the energy distribution and equation of state of the universe between the end of inflation and the onset of radiation domination (RD), considering observationally consistent single-field inflationary scenarios, with a potential 'flattening' at large field values, and a monomial shape $V(\varphi )\propto |\varphi {|}^p$ around the origin. As a proxy for (p)reheating, we include a quadratic interaction $g^2{\varphi }^2{X}^2$ between the inflaton $\varphi$ and a light scalar 'daughter' field $X$, with $g^2>0$. We capture the non-perturbative and non-linear nature of the system dynamics with lattice simulations, obtaining that: $i)$ the final energy transferred to $X$ depends only on $p$, not on $g^2$, ; $ii)$ the final transfer of energy is always negligible for $2\le p<4$, and of order $\sim 50\%$ for $p\ge 4$; $iii)$ the system goes at late times to matter-domination for $p=2$, and always to RD for $p>2$. In the latter case we calculate the number of e-folds until RD, significantly reducing the uncertainty in the inflationary observables $n_s$ and $r$.

    ↳ astro-ph.COhep-phhep-thPLB(2020)·65 citations
13. 13*

    Asymptotically Safe QED

    Holger Gies🇩🇪 · Jobst Ziebell🇩🇪

    High-energy completeness of quantum electrodynamics (QED) can be induced by an interacting ultraviolet fixed point of the renormalization flow. We provide evidence for the existence of two of such fixed points in the subspace spanned by the gauge coupling, the electron mass and the Pauli spin-field coupling. Renormalization group trajectories emanating from these fixed points correspond to asymptotically safe theories that are free from the Landau pole problem. We analyze the resulting universality classes defined by the fixed points, determine the corresponding critical exponents, study the resulting phase diagram, and quantify the stability of our results with respect to a systematic expansion scheme. We also compute high-energy complete flows towards the long-range physics. We observe the existence of a renormalization group trajectory that interconnects one of the interacting fixed points with the physical low-energy behavior of QED as measured in experiment. Within pure QED, we estimate the crossover from perturbative QED to the asymptotically safe fixed point regime to occur somewhat above the Planck scale but far below the scale of the Landau pole.

    ↳ hep-thhep-phEPJC(2020)·25 citations
14. 14*

    Geometry creates inertia

    Amitabha Lahiri🇮🇳

    The dynamics of fermions in curved spacetime is governed by a spin connection, a part of which is contorsion, an auxiliary field independent of the metric, without dynamics but fully expressible in terms of the axial current density of fermions. Its effect is the appearance of a quartic interaction involving all fermions. Contorsion can couple to left and right-handed fermions with different strengths, leading to an effective mass for fermions propagating on a background containing fermionic matter.

    ↳ gr-qchep-phInt.J.Mod.Phys.D(2020)·2 citations
15. 15*

    Pair Production and Gravity as the Weakest Force

    Eduardo Gonzalo🇪🇸 · Luis E. Ibáñez🇪🇸

    The Weak Gravity Conjecture (WGC) is usually formulated in terms of the stability of extremal black-holes or in terms of long distance Coulomb/Newton potentials. However one can think of other physical processes to compare the relative strength of gravity versus other forces. We argue for an alternative formulation in terms of particle pair production at threshold or, equivalently, pair annihilation at rest. Imposing that the production rate by any force mediator (photon or scalar) of pairs of charged particles be larger or equal to graviton production, we recover known conditions for the $U(1)$ WGC and its extensions. Unlike other formulations though, threshold pair production is sensitive to short range couplings present in scalar interactions and gives rise to a Scalar WGC. Application to moduli scalars gives rise to specific conditions on the trilinear and quartic couplings which involve first and second derivatives of the WGC particle mass with respect to the moduli. Some extremal solutions to these equations correspond to massive states behaving like BPS, KK and winding states which feature duality invariance and are in agreement with the Swampland distance conjecture. Conditions for $N=2$ BPS states saturate our bounds and we discuss specific examples of BPS states which become massless at large Kahler moduli in Type IIA N=2, D=4 CY and orbifold compactifications. We study possible implications for potentials depending on moduli only through WGC massive states. For some simple classes of potentials one recovers constraints somewhat similar but not equivalent to a Swampland dS conjecture.

    ↳ hep-thhep-phJHEP(2020)·30 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.