| 1. |
- Antipin, Oleg, et al.
(författare)
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Minimal Coleman-Weinberg theory explains the diphoton excess
- 2016
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Ingår i: PHYSICAL REVIEW D. - : American Physical Society. - 2470-0010. ; 93:11
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Tidskriftsartikel (refereegranskat)abstract
- We replace the standard Higgs-mechanism by the Coleman-Weinberg mechanism, and investigate its viability through the addition of a new scalar field. As we showed in a previous study, minimal models of this type can alleviate the hierarchy problem of the Higgs-mass through the so-called Veltman conditions. We here extend the previous analysis by taking into account the important difference between running mass and pole mass of the scalar states. We then investigate whether these theories can account for the 750 GeV excess in diphotons observed by the LHC collaborations. New QCD-colored fermions in the TeV mass range coupled to the new scalar state are needed to describe the excess. We further show, by explicit computation of the running of the couplings, that the model is under perturbative control till just above the masses of the heaviest states of the theory. We further suggest related testable signatures and thereby show that the LHC experiments can test these models.
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| 2. |
- Bi, Huan-Yu, et al.
(författare)
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Degeneracy relations in QCD and the equivalence of two systematic all-orders methods for setting the renormalization scale
- 2015
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Ingår i: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 748, s. 13-18
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Tidskriftsartikel (refereegranskat)abstract
- The Principle of Maximum Conformality (PMC) eliminates QCD renormalization scale-setting uncertainties using fundamental renormalization group methods. The resulting scale-fixed pQCD predictions are independent of the choice of renormalization scheme and show rapid convergence. The coefficients of the scale-fixed couplings are identical to the corresponding conformal series with zero beta-function. Two all-orders methods for systematically implementing the PMC-scale setting procedure for existing high order calculations are discussed in this article. One implementation is based on the PMC-BLM correspondence (PMC-I); the other, more recent, method (PMC-II) uses the R-delta-scheme, a systematic generalization of the minimal subtraction renormalization scheme. Both approaches satisfy all of the principles of the renormalization group and lead to scale-fixed and scheme-independent predictions at each finite order. In this work, we show that PMC-I and PMC-II scale-setting methods are in practice equivalent to each other. We illustrate this equivalence for the four-loop calculations of the annihilation ratio Re+e- and the Higgs partial width Gamma(H -> b (b) over bar). Both methods lead to the same resummed ('conformal') series up to all orders. The small scale differences between the two approaches are reduced as additional renormalization group {beta(i)}-terms in the pQCD expansion are taken into account. We also show that special degeneracy relations, which underly the equivalence of the two PMC approaches and the resulting conformal features of the pQCD series, are in fact general properties of non-Abelian gauge theory. (C) 2015 The Authors. Published by Elsevier B.V.
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| 3. |
- Di Vecchia, Paolo, et al.
(författare)
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Double-soft behavior for scalars and gluons from string theory
- 2015
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Ingår i: Journal of High Energy Physics (JHEP). - : Springer. - 1126-6708 .- 1029-8479. ; 2015:12, s. 1-23
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Tidskriftsartikel (refereegranskat)abstract
- Abstract: We compute the leading double-soft behavior for gluons and for the scalars obtained by dimensional reduction of a higher dimensional pure gauge theory, from the scattering amplitudes of gluons and scalars living in the world-volume of a Dp-brane of the bosonic string. In the case of gluons, we compute both the double-soft behavior when the two soft gluons are contiguous as well as when they are not contiguous. From our results, that are valid in string theory, one can easily get the double-soft limit in gauge field theory by sending the string tension to infinity.
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| 4. |
- Di Vecchia, Paolo, et al.
(författare)
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Double-soft behavior of the dilaton of spontaneously broken conformal invariance
- 2017
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Ingår i: Journal of High Energy Physics (JHEP). - : Springer. - 1126-6708 .- 1029-8479. ; 2017:9
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Tidskriftsartikel (refereegranskat)abstract
- The Ward identities involving the currents associated to the spontaneously broken scale and special conformal transformations are derived and used to determine, through linear order in the two soft-dilaton momenta, the double-soft behavior of scattering amplitudes involving two soft dilatons and any number of other particles. It turns out that the double-soft behavior is equivalent to performing two single-soft limits one after the other. We confirm the new double-soft theorem perturbatively at tree-level in a D-dimensional conformal field theory model, as well as nonperturbatively by using the "gravity dual" of N = 4 super Yang-Mills on the Coulomb branch; i.e. the Dirac-Born-Infeld action on AdS(5) x S-5.
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| 5. |
- Di Vecchia, Paolo, et al.
(författare)
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Multiloop soft theorem for gravitons and dilatons in the bosonic string
- 2019
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Ingår i: Journal of High Energy Physics (JHEP). - : SPRINGER. - 1126-6708 .- 1029-8479. ; :1
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Tidskriftsartikel (refereegranskat)abstract
- We construct, in the closed bosonic string, the multiloop amplitude involving N tachyons and one massless particle with 26 - D compactified directions, and we show that at least for D > 4, the soft behaviors of the graviton and dilaton satisfy the same soft theorems as at the tree level, up to one additional term at the subsubleading order, which can only contribute to the dilaton soft behavior and which we show is zero at least at one loop. This is possible, since the infrared divergences due to the non-vanishing tachyon and dilaton tadpoles do not depend on the number of external particles and are therefore the same both in the amplitude with the soft particle and in the amplitude without the soft particle. Therefore this leaves unchanged the soft operator acting on the amplitude without the soft particle. The additional infrared divergence appearing for D 4 depend on the number of external legs and must be understood on their own.
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| 6. |
- Di Vecchia, Paolo, et al.
(författare)
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Multiloop soft theorem of the dilaton in the bosonic string
- 2019
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Ingår i: Physical Review D. - : AMER PHYSICAL SOC. - 2470-0010 .- 2470-0029. ; 100:4
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Tidskriftsartikel (refereegranskat)abstract
- We show that by fixing the multiloop Green function in the closed bosonic string to be Arakelov's Green function, one obtains factorization of scattering amplitudes with a softly emitted dilaton to the same level as with a graviton to all loop order. This extends our previous analysis at one loop to all loop orders and confirms that some high-energy quantum symmetry in the bosonic string protects the factorization of amplitudes with softly emitted dilatons.
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| 7. |
- Di Vecchia, Paolo, et al.
(författare)
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New soft theorems for the gravity dilaton and the Nambu-Goldstone dilaton at subsubleading order
- 2016
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Ingår i: PHYSICAL REVIEW D. - 2470-0010. ; 93:8
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Tidskriftsartikel (refereegranskat)abstract
- We study the soft behavior of two seemingly different particles that are both referred to as dilatons in the literature, namely the one that appears in theories of gravity and in string theory and the Nambu-Goldstone boson of spontaneously broken conformal invariance. Our primary result is the discovery of a soft theorem at subsubleading order for each dilaton, which in both cases contains the operator of special conformal transformations. Interesting similarities as well as differences between the dilaton soft theorems are discussed.
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| 8. |
- Di Vecchia, Paolo, et al.
(författare)
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Soft behavior of a closed massless state in superstring and universality in the soft behavior of the dilaton
- 2016
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Ingår i: Journal of High Energy Physics (JHEP). - : Springer. - 1126-6708 .- 1029-8479. ; :12
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Tidskriftsartikel (refereegranskat)abstract
- We consider the tree-level scattering amplitudes in the NS-NS (Neveu-Schwarz) massless sector of closed superstrings in the case where one external state becomes soft. We compute the amplitudes generically for any number of dimensions and any number and kind of the massless closed states through the subsubleading order in the soft expansion. We show that, when the soft state is a graviton or a dilaton, the full result can be expressed as a soft theorem factorizing the amplitude in a soft and a hard part. This behavior is similar to what has previously been observed in field theory and in the bosonic string. Differently from the bosonic string, the supersymmetric soft theorem for the graviton has no string corrections at subsubleading order. The dilaton soft theorem, on the other hand, is found to be universally free of string corrections in any string theory.
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| 9. |
- Di Vecchia, Paolo, et al.
(författare)
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Soft theorem for the graviton, dilaton and the Kalb-Ramond field in the bosonic string
- 2015
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Ingår i: Journal of High Energy Physics (JHEP). - 1126-6708 .- 1029-8479. ; :5
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Tidskriftsartikel (refereegranskat)abstract
- We study the behavior of the scattering amplitudes of the bosonic string involving a soft massless state (graviton, dilaton and Kalb-Ramond antisymmetric tensor) and closed string tachyons or other closed string massless states. For a soft graviton we confirm the results, obtained in ref. [37] using just gauge invariance, up to terms of O(q(1)) for external tachyons and up to terms of O(q(0)) for external massless closed string states. Furthermore, we also derive the behavior of the scattering amplitude when a dilaton or a Kalb-Ramond field becomes soft. These results are new and cannot, to our knowledge, be derived by using gauge invariance. It turns out, in the cases examined, that the soft amplitude for a dilaton or for an antisymmetric tensor is obtained by saturating the tensor, M (mu nu) , derived from gauge invariance for gravitons, with their respective polarization tensors. Thus extra terms that could have appeared in M (mu nu) in the case of a soft dilaton, in fact do not appear.
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| 10. |
- Di Vecchia, Paolo, et al.
(författare)
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Soft Theorems from String Theory
- 2016
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Ingår i: Fortschritte der Physik. - : Wiley-VCH Verlagsgesellschaft. - 0015-8208 .- 1521-3978. ; 64:4-5, s. 389-393
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Tidskriftsartikel (refereegranskat)abstract
- Soft behaviour of closed string amplitudes involving dilatons, gravitons and anti-symmetric tensors, is studied in the framework of bosonic string theory. The leading double soft limit of gluons is analysed as well, starting from scattering amplitudes computed in the open bosonic string. Field theory expressions are then obtained by sending the string tension to infinity. The presented results have been derived in the papers of Ref [1].
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