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Manoj K. Yadav

Publications and source records attributed to Manoj K. Yadav.

At least 19 recordsLinked to original sources
arXiv2026

Commuting probability of skew left braces

We introduce a concept of the commuting probability of a skew left brace analogous to group theory. We establish upper and lower bounds for the commuting probability and prove that, for finite non-trivial skew left braces, it is always at most $\frac{3}{4}$. Interestingly, there is no skew left brace with commuting probability in the open interval $(5/8, 1)$, except $\frac{3}{4}$, for which we construct an explicit example. A characterization of skew left braces having commuting probability $\frac{3}{4}$ or $\frac{5}{8}$ is presented. We further show that the finite skew left braces with commuting probability larger than $\frac{65}{128}$ are necessarily nilpotent. We prove that the commuting probability remains invariant under isoclinism of skew braces. We introduce a concept of a compact Hausdorff topological skew left brace $B$, where we prove that the set of all elements of $B$ having finite centraliser index in $B$ is a Borel subgroup. For such infinite non-trivial skew left braces too $\frac{3}{4}$ is the upper bound for the commuting probability, and $\frac{3}{4}$ is the only rational number which occurs as commuting probability in the open interval $(5/8, 1)$.

math.GR↗
arXiv2026

Skew brace extensions, second cohomology and complements

We study extensions and second cohomology of skew left braces via the natural semi-direct products associated with the skew left braces. Let $0 \to I \to E \to H \to 0$ be a skew brace extension and $Λ_H$ denote the natural semi-direct products associated with the skew left brace $H$. We establish a group homomorphism from ${\rm H}_{Sb}^2(H, I)$ into ${\rm H}_{Gp}^2(Λ_H, I \times I)$, which turns out to be an embedding when $I \le {\rm Soc}(E)$. In particular the Schur multiplier of a skew left braces $H$ embeds into the Schur multiplier of the group $Λ_H$. Analog of the Schur-Zassenhaus theorem is established for skew left braces in several specific cases. We introduce a concept called minimal extensions (which stay at the extreme end of split extensions) of skew left braces and derive many fundamental results. Several reduction results for split extensions of finite skew left braces by abelian groups (viewed as trivial left braces) are obtained.

math.GR↗
arXiv2025

Central series' and ($n$)-isoclinism of skew left braces

The aim of this article is to advance the knowledge on the theory of skew left braces. We introduce a subclass of skew left braces, which we denote by $\mathcal{I}_n$, $n \ge 1$, such that elements of the annihilator and lower central series' interact `nicely' with respect to commutation. That allows us to define a concept of $n$-isoclinism of skew left braces in $\mathcal{I}_n$, by using a concept of brace commutator words, which we have introduced. We prove results on $1$-isoclinism (isoclinism) of skew left braces analogous to important results in group theory. For any two symmetric $n$-isoclinic skew left braces $A$ and $B$, we prove that, there exist skew left braces $C$ and $R$ such that both $A$ and $B$ are $n$-isoclinic to both $C$ and $R$ and (i) $A$ and $B$ are quotient skew left braces of $C$; (ii) $A$ and $B$ are sub-skew left braces of $R$. Connections between a skew left brace and the group which occurs as a natural semi-direct product of additive and multiplicative groups of the skew left brace are investigated, and it is proved that $n$-isoclinism is preserved from braces to groups. We also show that various nilpotency concepts on skew left braces are invariant under $n$-isoclinism.

math.RA↗
arXiv2023

Symmetric skew braces and brace systems

For a skew left brace $(G, \cdot, \circ)$, the map $λ: (G, \circ) \to \Aut \,(G, \cdot),~~a \mapsto λ_a,$ where $λ_a(b) = a^{-1} \cdot (a \circ b)$ for all $a, b \in G$, is a group homomorphism. Then $λ$ can also be viewed as a map from $(G, \cdot)$ to $\Aut \, (G, \cdot)$, which, in general, may not be a homomorphism. A skew left brace will be called $λ$-anti-homomorphic ($λ$-homomorphic) if $λ: (G, \cdot) \to \Aut \, (G, \cdot)$ is an anti-homomorphism (a homomorphism). We mainly study such skew left braces. We device a method for constructing a class of binary operations on a given set so that the set with any two such operations constitute a $λ$-homomorphic symmetric skew brace. Most of the constructions of symmetric skew braces dealt with in the literature fall in the framework of our construction. We then carry out various such constructions on specific infinite sets.

math.RA↗
arXiv2021

Commutators in groups of order $p^7$

We present a characterisation of groups $G$ of order $p^7$, $p$ prime, in which not all elements of the commutator subgroup $γ_2(G)$ of $G$ are commutators in $G$. On the way we obtain several structural results on groups of order $p^7$.

math.GR↗
arXiv2021

Cohomology, Extensions and Automorphisms of Skew Braces

The second cohomology group of a left skew brace with coefficients in a trivial left brace with non-trivial actions is defined, its connection with extensions of a left skew brace by a trivial braces is established and a Wells' like exact sequence relating the second cohomology group with inducible automorphisms of an extension of left skew braces is constructed.

math.GR↗
arXiv2020

Converse of Schur's Theorem - A statement

Let $G$ be an arbitrary group such that $G/\Z(G)$ is finite, where $\Z(G)$ denotes the center of the group $G$. Then $γ_2(G)$, the commutator subgroup of $G$, is finite. This result is known as Shur's theorem (the Schur's theorem). In this short note we provide a quick survey on the converse of Schur's theorem, generalize known results in this direction and prove the following result (which is perhaps the most suitable statement for converse of the Schur's theorem): If $G$ is an arbitrary group with finite $γ_2(G)$, then $G/\Z(G)$ is finite if $\Z_2(G)/\Z(\Z_2(G))$ is finitely generated, where $\Z_2(G)$ denotes the second center of a group $G$. If $G/\Z(G)$ is finite, then $γ_2(G)$ is also finite and $|G/\Z(G)| \le |γ_2(G)|^d$, where $d$ denotes the number of elements in any minimal generating ser for $G/\Z(G)$. We classify all nilpotent groups $G$ of class 2 upto isoclinism (in the sense of P. Hall) such that $|G/\Z(G)| = |γ_2(G)|^d$, and ask some questions in the sequel.

math.GR↗
arXiv2020

Modeling Control, Lockdown \& Exit Strategies for COVID-19 Pandemic in India

COVID-19--a viral infectious disease--has quickly emerged as a global pandemic infecting millions of people with a significant number of deaths across the globe. The symptoms of this disease vary widely. Depending on the symptoms an infected person is broadly classified into two categories namely, asymptomatic and symptomatic. Asymptomatic individuals display mild or no symptoms but continue to transmit the infection to otherwise healthy individuals. This particular aspect of asymptomatic infection poses a major obstacle in managing and controlling the transmission of the infectious disease. In this paper, we attempt to mathematically model the spread of COVID-19 in India under various intervention strategies. We consider SEIR type epidemiological models, incorporated with India specific social contact matrix representing contact structures among different age groups of the population. Impact of various factors such as presence of asymptotic individuals, lockdown strategies, social distancing practices, quarantine, and hospitalization on the disease transmission is extensively studied. Numerical simulation of our model is matched with the real COVID-19 data of India till May 15, 2020 for the purpose of estimating the model parameters. Our model with zone-wise lockdown is seen to give a decent prediction for July 20, 2020.

q-bio.PE↗
arXiv2020

On $λ$-homomorphic skew braces

For a skew left brace $(G, \cdot, \circ)$, the map $λ: (G, \circ) \to \mathrm{Aut} \;(G, \cdot),~~a \mapsto λ_a$, where $λ_a(b) = a^{-1} \cdot (a \circ b)$ for all $a, b \in G$, is a group homomorphism. Then $λ$ can also be viewed as a map from $(G, \cdot)$ to $\mathrm{Aut}\; (G, \cdot)$, which, in general, may not be a homomorphism. We study skew left braces $(G, \cdot, \circ)$ for which $λ: (G, \cdot) \to \mathrm{Aut}\; (G, \cdot)$ is a homomorphism. Such skew left braces will be called $λ$-homomorphic. We formulate necessary and sufficient conditions under which a given homomorphism $λ: (G, \cdot) \to \mathrm{Aut}\; (G, \cdot)$ gives rise to a skew left brace, which, indeed, is $λ$-homomorphic. As an application, we construct skew left braces when $(G, \cdot)$ is either a free group or a free abelian group. We prove that any $λ$-homomorphic skew left brace is an extension of a trivial skew brace by a trivial skew brace. Special emphasis is given on $λ$-homomorphic skew left brace for which the image of $λ$ is cyclic. A complete characterization of such skew left braces on the free abelian group of rank two is obtained.

math.RA↗
arXiv2019

Computing skew left braces of small orders

We improve Algorithm 5.1 of [Math. Comp. {\bf 86} (2017), 2519-2534] for computing all non-isomorphic skew left braces, and enumerate left braces and skew left braces of orders up to 868 with some exceptions. Using the enumerated data, we state some conjectures for further research.

math.RA↗
arXiv2019

$p$-Power conjugacy classes in $U(n,q)$ and $T(n,q)$

Let $q$ be a $p$-power where $p$ is a fixed prime. In this paper, we look at the $p$-power maps on unitriangular group $U(n,q)$ and triangular group $T(n,q)$. In the spirit of Borel dominance theorem for algebraic groups, we show that the image of this map contains large size conjugacy classes. For the triangular group we give a recursive formula to count the image size.

math.GR↗
arXiv2018

The Schur Multipliers of $p$-Groups of Order $p^5$

In this article, we compute the Schur multiplier, non-abelian tensor square and exterior square of non-abelian $p$-groups of order $p^5$. As an application we determine the capability of groups of order $p^5$.

math.GR↗
arXiv2017

The Schur multiplier of central product of groups

Let $G$ be a central product of two groups $H$ and $K$. We study second cohomology group of $G$, having coefficients in a divisible abelian group $D$ with trivial $G$-action, in terms of the second cohomology groups of certain quotients of $H$ and $K$. In particular, for $D = \mathbb{C}^{*}$, some of our results provide a refinement of results from [Some groups with non-trivial multiplicators, Math. Z. {\bf 120 } (1971), 307-308] and [On the Schur multiplicator of a central quotient of a direct product of groups, J. Pure Appl. Algebra {\bf 3} (1973), 73-82].

math.GR↗
arXiv2017

Finite $p$-Groups of Nilpotency Class $3$ with Two Conjugacy Class Sizes

It is proved that, for a prime $p>2$ and integer $n\geq 1$, finite $p$-groups of nilpotency class $3$ and having only two conjugacy class sizes $1$ and $p^n$ exist if and only if $n$ is even; moreover, for a given even positive integer, such a group is unique up to isoclinism (in the sense of Philip Hall).

math.GR↗
arXiv2016

Note on Caranti's Method of Construction of Miller groups

The non-abelian groups with abelian group of automorphisms are widely studied. Following Earnley, such groups are called Miller groups, since the first example of such a group was given by Miller in 1913. Many other examples of Miller $p$-groups have been constructed by several authors. Recently, A. Caranti [{\it Israel J. Mathematics {\bf 205} (2015), 235-246}] provided module theoretic methods for constructing non-special Miller $p$-groups from special Miller $p$-groups. By constructing examples, we show that these methods do not always work. We also provide a sufficient condition on special Miller $p$-group for which the methods of Caranti work.

math.GR↗