Past
Class number and quadratic forms
Speaker:Devika Sharma (School of Maths, TIFR)
Date: Tuesday, 14th February, 2012
Time: 02:30 pm
Venue: AG-77
Abstract: Given a quadratic field extension K over Q, of discriminant d, the class number of K has a very interesting relation to the set of quadratic forms of the same discriminant d.
This relation makes the computation of the class number of K, famously a tough problem, much easy. In the talk I will sufficiently explain all the terms used and give an explicit proof of the correspondence.
Multivariable calculus in Analysis and in Algebra
Speaker:Nitin Nitsure (School of Maths, TIFR)
Date: Wednesday, 8th February, 2012
Time: 04:00 pm
Venue: AG-77
Abstract: Not available.
An Introduction to the Circle Method
Speaker:A. Sankaranarayanan (School of Maths, TIFR)
Date: Monday, 30th January, 2012 and Wednesday, 1st February, 2012
Time: 10.30 am
Venue: AG-77
Abstract:These two lectures meant for graduate students will be overviewing the circle method about the development starting from Ramanujan, Hardy, Littlewood, Vinogradov and Rademacher. We will try to explain the origin of the method, some improvements and some applications avoiding technical details.
Introduction to Perverse Sheaves
Speaker:Vaibhav Vaish (School of Maths, TIFR)
Date: Tuesday, 24th January, 2012
Time: 2:30pm
Venue: AG-77
Abstract:We aim to introduce the category of Perverse Sheaves over a reasonable topological space. The construction is mostly formal once we have the notion of sheaves and their push-forwards and pullbacks. The talk should be accessible to all.
Siegel modular forms for the paramodular group
Speaker:Rainer Schulze-Pillot (Universitat des Saarlandes, Saarbrucken, Germany)
Date: Tuesday, 17th January, 2012
Time: 2:30pm
Venue: AG-77
Abstract:Siegel modular forms are particular holomorphic functions on a generalized upper half plane which have good transformation behaviour under some discrete subgroup of the real symplectic group and are of importance in number theory. Most of the time one studies such forms whith respect to congruence subgroups of the integral symplectic group, but recently also the paramodular groups have gained interest; these are arithmetic groups which can not be conjugated into the integral symplectic group.
In this talk I define the relevant notions and show how to construct theta series associated to quadratic forms which are modular with respect to the paramodular group.
An introduction to the representation theory and the Zeta functions of divison algebras
Speaker: Dinakar Ramakrishnan (Caltech, USA)
Date: 13th January, 2012 (Friday)
Time: 2:30pm
Venue: AG-77
Abstract:Not available.
The u-invariant of a field
Speaker: R. Parimala (Emory University, USA)
Date: 29th December, 2011 (Thursday)
Time: 5:00pm
Venue: AG-77
Abstract:Not available.
The Riemann-Roch Theorem
Speaker: M.V. Nori (University of Chicago, USA)
Date: 23rd December, 2011 (Friday)
Time: 2:30pm
Venue: AG-77
Abstract:Not available.
Unique decomposition of tensor products of irreducible representations of simple Lie algebras
Speaker:R. Venkatesh (TIFR)
Date: 2nd December, 2011 (Friday)
Time: 2:30pm
Venue: AG-77
Abstract:Prof. C.S. Rajan proved that the tensor product of irreducible, finite dimensional representations of a simple Lie algebra over a field of
characteristic zero determines the individual constituents uniquely. This is analogous to the uniqueness of prime factorization of natural numbers. We will see a different proof of the Rajan's result and discuss some generalizations. We will begin with a brief introduction to Lie algebras. The talk will be accessible to all.
An Introduction to Riemann zeta function theory
Speaker:Saurabh Kumar Singh (TIFR)
Date: 25th November, 2011 (Friday)
Time: 2:30pm
Venue: AG-77
Abstract:We shall define Riemann zeta function $\zeta (s)$ and give it's Euler product form. Then we shall explain the functional equation for $\zeta(s)$ and some zero free region of $\zeta(s)$.
Some refinements of Serre's mass formula in prime degree.
Speaker: C. S. Dalawat (HRI, Allahabad)
Date: 18th November, 2011 (Friday)
Time: 2:30pm
Venue: AG-77
Abstract:We shall recall and motivate the statement of Serre's mass formula, which basically counts the number of separable extensions of a given degree of a local field with finite residue field. We shall then show how to refine this formula in the case of prime degree to count the number of cyclic extensions, or those with a given Galois group. The talk is going to be accessible to a wide audience. In particular, no background knowledge of the theory of local fields will be be assumed.
Transitive action of elementary matrices on the space of unimodular rows
Speaker: Sagnik Chakraborty (School of Maths, TIFR)
Date: 11th November, 2011 (Friday)
Time: 2:30pm
Venue: AG-77
Abstract:Let $R$ be a commutative noetherian ring with unity. In this seminar we shall discuss different conditions under which $E_n(R)$, $E_n(R[\underline{X}])$ act transitively on corresponding unimodular spaces.
Reciprocity laws
Speaker: Supriya Pisolkar (School of Maths, TIFR)
Date: 4th November, 2011 (Friday)
Time: 2:30pm
Venue: AG-77
Abstract:The law of quadratic reciprocity has fascinated mathematicians for over 300 years. As a graduate student one learns Artin's reciprocity law, cyclotomic reciprocity law. But then there is also" Abelian" and "Non-abelian " reciprocity laws. Shimura's theorem is also called as reciprocity law. A natural question is " What is the general reciprocity problem"?
One form of this problem is one of the basic consequence of the Langland's program, namely the law governing the primes modulo which integral polynomial splits completely. We will give an elementary introduction to this.
Topics in singularity theory
Speaker: A.J.Parameswaran (School of Maths, TIFR)
Date: 21st October, 2011 (Friday)
Time: 2:30pm
Venue: AG-77
Abstract: We will begin with `local Lefschetz' theory and proceed to indicate the `Milnor's Fibration Theorem'. Then we analyze the `Milnor Fibre'. Also interpret the Milnor Number algebraically and topologically. The proofs will be sketchy and topological/geometric.
Then (if time permits) we move onto some results about equisingular families and discuss some "OPEN PROBLEMS"..
Main references will be
1. John Milnor, Singular Points of Complex Hypersurfaces. Princeton University Press.
2. Klaus Lamotke, The Topology of Complex Projective Varieties after S. Lefschetz, Topology Vol. 20 1981. pp. 15-51.
Supplementary reading:
3. E.J.N. Loojenga, Isolated Singular Points on Complete Intersections, London Mathematical Society Lecture Notes series 77.
4. J. Milnor, Morse Theory.
Topological quantum field theory
Speaker: Yogish Holla (School of Maths, TIFR)
Date: 14th October, 2011 (Friday)
Time: 2:30pm
Venue: AG-77
Abstract: Not available.
Surveying representation theory
Speaker: Steven Thomas Spallone (School of Maths, TIFR)
Date: 7th October, 2011 (Friday)
Time: 2:30pm
Venue: AG-77
Abstract:We introduce the main areas and ideas in representation theory. This talk is a survey meant for graduate students who have seen some representation theory of finite groups and want a sense of areas with names like "representation theory of p-adic groups". Perhaps some day you will be working in one of these areas.
$abc-$ conjecture-- easily said than done.
Speaker: N. Saradha (School of Maths, TIFR)
Date: 30th September, 2011 (Friday)
Time: 2:30pm
Venue: AG-77
Abstract:In this talk, I shall explore the origin of $abc-$ conjecture and give some applications to Diophantine equations.
Quadratic reciprocity, Gauss' first proof and K-theory.
Speaker: C.S. Rajan (School of Maths, TIFR)
Time: Friday, 23rd September, 2:30pm
Venue: AG-77
Abstract:No abstract available.
Linear relations among Poincare series
Speaker: Soumya Das (School of Maths, TIFR)
Time: Friday, 16th September, 2:30pm
Venue: AG-77
Abstract:We will define modular forms on congruence subgroups of the modular group and introduce the Poincare series, which are special cusp forms. We will discuss a generalisation of the famous Lehmer's question on the non-vanishing of the Ramanujan's \tau-function; which is a special case of characterising all linear relations among Poincare series. There has been some work on this by Choie-Kohnen-Ono. I will review that and discuss some recent results related to this question, which is a joint work with Satadal Ganguly. The talk will be accessible to all.
An Invitation to Geometric Group Theory
Speaker: Pranab Sardar (Ramakrishna Mission Vivekanand University, Kolakata)
Time: Friday, 09th September, 2:30pm
Venue: AG-77
Abstract:I will introduce quasi-isometric embeddings of metric spaces and mention some properties of spaces invariant under quasi-isometries. Hyperbolic spaces, and groups will be introduced and some of their basic properties will be mentioned. Most of the statements will be without proofs to avoid technicality and to improve transparency; the goal is to give the audience some flavour of the subject and the content of the talk is quite standard.
References:
1. Metric spaces of nonpositive curvature- Bridson and Haefliger,
2. Group theory from a geometrical viewpoint- ed. Ghys, Haefliger, Verjovsky et al.
3. Hyperbolic groups- Gromov, in "Essays in Group Theory" (ed. S.M.Gersten),
4. Notes by
Brian Bowditch.
The Chern-Weil Theory
Speaker: M.S. Raghunathan (School of Maths, TIFR)
Time: Tuesday, 6th September, 4:00pm
Venue: AG-77
Abstract:
The Torelli Theorem
Speaker: Sanjay Kumar Singh (School of Maths, TIFR)
Time: Friday, 26th August, 2:30pm
Venue: AG-77
Abstract:The Torelli theorem states that the map M_g to A_g from the moduli space of curves of genus g, to the moduli space of principally polarized abelian varieties, is injective (on geometric points). This map takes a curve X to its Jacobian J(X). I will start from compact Riemann surfaces and then explain its canonically polarized Jacobians. If time permits; I will state some more Torelli-type theorems.
References:
1.Henrik H. Martens. A new proof of Torelli's theorem.
Ann. of Math, 78, p 107-111, 1963.
2.A. Andreotti. On Torelli's theorem. Am. J. Math, 80, p 801-821, 1958.
The Vaserstein symbol in dimension two
Speaker: Ravi A. Rao (School of Maths, TIFR)
Time: Friday, 19th August, 2:30pm
Venue: AG-77
Abstract:A beautiful theorem of L.N. Vaserstein in the mid-seventies, prior to the Serre's conjecture being solved in late seventies, describes an abelian group structure on the orbit space of unimodular rows of length three modulo elementary action over a two dimensional ring. We revisit this theorem, and explain why it is of importance even today.
On the Milnor Conjecture (Voevodsky's Theorem)
Speaker: Anand Sawant (School of Maths, TIFR)
Time: Friday, 12th August, 2:00pm
Venue: AG-77
Abstract:The Milnor Conjecture was posed by John Milnor in 1970 to give a description of the Milnor K-theory ring of a field F of characteristic different from 2 by means of the graded Witt ring of F, which is determined by the quadratic forms over F. The Milnor Conjecture was proved by Vladimir Voevodsky, for which he was awarded the Fields medal in 2002.
We shall begin with a glimpse of classical algebraic K-theory, which motivates the definition of Milnor K-theory. We then introduce the Witt ring of a field and describe the Milnor Conjecture and its various versions. If time permits, we shall give a very brief sketch of the steps in Voevodsky's proof of the Milnor Conjecture.
This talk is meant to be a first introduction to the Milnor Conjecture and will be accessible to all.
An Introduction to Toric Varieties
Speaker: Vaibhav Vaish (School of Maths, TIFR)
Time: Monday, 8th August, 2:30pm
Venue: AG-77
Abstract:Toric Varieties are a class of algebraic varieties which admit a combinatorial description in terms of polytopes in the usual euclidean space.
Although this class is very special (for example, all varieties in this class are rational, and have only rational singularities), it is broad enough to include many common varieties (eg Affine space, Projective space, Grassmannians). On the other hand various geometric properties and operations (like smoothness, proper-ness, projective-ness, blow ups, de-singularizations) have simple combinatorial description and otherwise in-accessible invariants (like
Betti numbers, Chow groups) can be often effectively computed. This makes toric varieties a good test case for otherwise inaccessible conjectures, apart from their playing role in several constructions and proofs (for example in compactification of Shimura Varieties, or some results in resolution of singularities).
This talk is meant to be a first introduction to their construction and some basic properties. We will begin with a short introduction to Algebraic Geometry if there are first year students in the Audience, in which case the talk will exceed an hour by about fifteen minutes.
Forcing algebras and ideal closure operations
Speaker: Holger Brenner (University of Sheffield)
Time: Monday, 01st August, 2:30pm
Venue: AG-77
Abstract:In this expository talk I try to explain how ideal closure operations can be understood by studying properties of forcing algebras and their induced torsors. We will deal with the radical, integral closure, continuous clousure, tight closure and plus closure.
Modular curves and Modulariy
Speaker: Srilakshmi Krishnamoorthy (School of Maths, TIFR)
Time: Friday, 22nd July, 2:30pm
Venue: AG-77
Abstract:For any congruence subgroup $\Gamma$ of $SL_2(\Z)$ there is a corresponding modular curve $Y(\Gamma)$. The modular curves $Y(\Gamma_0(N)$,
associated with the congruence subgroups $\Gamma_0(N)$, for integer $N >=1$ parametrize elliptic curves over $\mathbb{C}$ with given a cyclic subgroup of order $N$, up to isomorphism. I will talk about modular curves and I'll state modularity theorems.
On the non-vanishing of Poincare series
Speaker: Jyoti Sengupta (School of Maths, TIFR)
Time: Monday, 18th July, 2:30pm
Venue: AG-77
Representation theory of $S_n$
Speaker: Ronnie M. Sebastian (School of Maths, TIFR)
Time: Friday, 08th July, 2:30pm
Venue: AG-77
Abstract:In this talk we will describe the irreducible representations of $S_n$ using Young diagrams.
Quadratic reciprocity and abelian extensions of Q
Speaker: Gerald Gotsbacher (School of Maths, TIFR)
Time: Friday, 01st July, 2:30pm
Venue: AG-77
Abstract:In this talk, I shall sketch a proof of Quadratic Reciprocity and show how to subsume it under abelian class field theory in the formulation of Weber, Hilbert and Takagi. Throughout concepts will be introduced by way of examples and only elementary operations will be performed, both on trivial and non-trivial results.
The Siegel zero
Speaker: Ritabrata Munshi (School of Maths, TIFR)
Time: Friday, 24th June, 2:30pm
Venue: AG-77
Abstract:The distribution of the zeros of L-functions inside the critical strip has intricate connections with fundamental arithmetic objects. For example, the famous Prime Number Theorem is equvalent to nonvanishing (no zeros) of the Riemann zeta function on the edge of the critical strip, and the Dirichlet's theorem about infinitude of primes in arithmetic progression is related to the nonvanishing of the Dirichlet L-function at the point 1 (again a boundary point of the critical strip). Another such connection is given by the relation between the size of the class group of an imaginary quadratic field and the ordinate of the Siegel zero (conjecturally nonexistential) of the corresponding L-function. In this talk our main focus will be this famous unsolved problem concerning the existence of the Siegel zero.
Super-rigidity and arithmeticity of higher rank lattices
Speaker: T.N. Venkataramana (School of Maths, TIFR)
Time: Friday, 17th June, 2:30pm
Venue: AG-77
Abstract:A sketch of the ideas going into the proof.
Iteration of rational functions
Speaker: N. Fakhruddin (School of Maths, TIFR)
Time: Friday, 10th June, 2:30pm
Venue: AG-77
Abstract:I will give a survey -- mostly without proofs -- of the basic results on the structure of the Fatou and Julia sets of a rational function in one variable over the field of complex numbers.
Towards the Kobayashi-Hitchin correspondence
Speaker: Matthias Stemmler (School of Maths, TIFR)
Time: Friday, 27th May, 2:30pm
Venue: AG-77
Abstract:The Kobayashi-Hitchin correspondence is an important classical result between algebraic and differential geometry. It states that a holomorphic vector bundle on a compact Kaehler manifold admits a Hermitian-Einstein metric if and only if it is polystable in the sense of Mumford-Takemoto. I will introduce the relevant notions around this statement in some detail, concluding with a precise formulation of the correspondence. If time permits, I will also give a very brief sketch of its proof.
Tannakian categories
Speaker: Amit Hogadi (School of Maths, TIFR)
Time: Friday, 20th May, 2:30pm
Venue: AG-77
Abstract:This will be an introductory talk on Tannakian categories and Tannakian duality.
On the fundamental group of hyperelliptic fibrations
Speaker: Shameek Paul (School of Maths, TIFR)
Time: Friday, 13th May, 2:30pm
Venue: AG-77
Abstract:This is a joint paper with Prof. R. V. Gurjar and B. P. Purnaprajna.
We prove that for a fibration on a surface (of general type) with irreducible (hyperelliptic) curves as fibers over a (possibly non-complete) curve, the image of the fundamental group of a general fiber in the fundamental group of the surface is finite. A (scheme-theoretic) fiber F = \sum n_i C_i is called a multiple fiber if its multiplicity := gcd(n_i | i) > 1. We also prove a striking result about the multiplicities of multiple fibers of similar smooth, projective surfaces.
Whittaker Model for $GL(n)$
Speaker: Shiv Prakash Patel (School of Maths, TIFR)
Time: Friday, 06th May, 2:30pm
Venue: AG-77
Abstract:We shall define a Whittaker model of an admissible representation for the algebraic group $GL(n)$. For a non-archimedean local field, we prove a "multiplicity one" theorem. More precisely, we prove that for an irreducible, admissible representation of $GL(n)$, the space of "Whittaker functionals" is of dimension at most one.
Action of Finite Reflection Groups on Graded Noetherian Rings
Speaker:Sagar Kolte (School of Maths, TIFR)
Time: Thursday, 29st April, 2:30pm
Venue: AG-77
Abstract: I will start by defining what it means to say that a n X n matrix is a pseudo-reflection, this will then be generalized to elements of a group G generated by pseudo-reflections acting on a graded Noetherian ring. The main result of the talk is as follows:
Let S be a Noetherian graded algebra over the complex numbers and let R be the sub-ring of elements fixed by G, then S is a finitely generated free R module. If time permits, I will mention a few results (without proof) by the way of applications.
Arakelov bundles over arithmetic curves
Speaker: Norbert Hoffmann (Freien Universitat Berlin)
Time: Thursday, 21st April, 2:30pm
Venue: AG-77
Abstract:The analogy between number fields and function fields of algebraic curves goes back at least to Dedekind and Weber (1882). Motivated by it, the set of all places of a number field is called an arithmetic curve. I'll explain analogues over arithmetic curves for a few statements about vector bundles over algebraic curves.
Borel's density theorem and related results
Speaker: S. G. Dani (School of Maths, TIFR)
Time: Friday, 15th April, 2:30pm
Venue: AG-77
Abstract:Let G be a locally compact group and H be a closed subgroup of G. We address the general problem of describing conditions under which given a representation of G over a finite-dimensional vector space V, every H-invariant subspace of V is also G-invariant. Such a property is of interest in various contexts. We shall discuss some results on the question, and their applications. The theme is an outgrowth of the classical theorem of A. Borel on "Zariski density of lattices in semisimple Lie groups", involving a particular case of the above.
Finite pseudo-reflection groups
Speaker:R. V. Gurjar (School of Maths, TIFR)
Time: Friday, 8th April, 2:30pm
Venue: AG-77
Abstract:Starting with the work of Shephard-Todd and Chevally about rings of invariants of these groups acting on polynomial rings, many important generalizations have been proved by Serre, Banwant Singh, Goto, Watanabe, Avramov,...I have now added a new result to this list. These results are important to understand singularities of quotients of complex manifolds by actions of discontinuous (in particular, finite) groups of complex analytic automorphisms.
In the lecture I will give a survey of this interesting area in Commutative Algebra and Algebraic Geometry, with hints for some proofs
'Siegel Sets' in $\SL_n(\R)$
Speaker:Sandip Singh (School of Maths, TIFR)
Time: Wednesday, 30th March, 2011, 11:15 am to 12:30 pm (possibly 20mins more after a short break)
Venue: AG-77
Abstract:We will define a Haar Measure on $\SL_n(\R)$ and prove that the 'Siegel set' in $\SL_n(\R)$ has finite volume. We will prove in this lecture that $\SL_n(\Z)$ is a lattice in $\SL_n(\R)$ by using the finiteness of the volume of the 'Siegel set'. Also, we will show that $\SL_n(\R)/\SL_n(\Z)$ is not compact. We will also discuss Haar measures on some subgroups of $\SL_n(\R)$. We will define all the terms used in proofs. We will need only the knowledge about Borel measures on topological spaces.
Characteristic Classes
Speaker:S. Ramanan (Chennai Mathematical Institute)
Time: Friday, 25th March, 2011, 2:30pm
Venue: AG-77
Abstract:
On the notion of Universal Connection in Differential Geometry
Speaker:M. S. Narasimhan (CAM,TIFR Bangalore)
Time: Friday, 18th March, 2011, 2:30pm
Venue: AG-77
Abstract:
Cauchy's Problem for Non-linear Hyperbolic Differential Equation in Two Independent Variables
Speaker:Manas Ranjan Sahoo (School of Maths, TIFR)
Time: Friday, 11th March, 2011, 2:30pm
Venue: AG-77
Abstract: Using a fixed point argument we will show a short time existence of the differential equation U_t + A(x,t,U) U_x + B(x,t,U) = o, where U(x,t)=(U_1,U_2,...,U_k) subject to the initial condition U(x,0)=\phi(x).
Studying designs via multisets
Speaker:Navin Singhi (School of Maths, TIFR)
Time: Friday, 4th March, 2011, 2:30pm
Venue: AG-77
Abstract: A design is a collection of subsets (called blocks) of a set $X$ (usually finite). Such a design is called a $t$-design if all $t$- subsets of $X$ are contained in the same number of blocks. Examples of $t$-designs include set of lines or higher dimensional subspaces etc. in affine, projective or some polar spaces.
The existence conjecture for $t$-designs states that such designs with large $\left|X\right|$ exist, whenever necessary parametric conditions are satisfied.
The degree of an element of $X$, in a given design, is the number of blocks containing it. The sequence of all such degrees is called the degree sequence of the design. A design is said to be simple if any subset of $X$ occurs as a block in it at most once. Classifying degree sequences of all simple designs is another well known unsolved problem. A lot of Discrete Mathematics developed, specially in the later half of last century, around problems of these types of parametric characterizations.
A new method, developed recently to study these types of problems by looking at multisets obtained as projections of blocks, will be discussed. Some other methods which have been used to study such problems, include viewing them as problem of finding integer point in a convex polytope with some symmetry and using Minkowski type theorems, using box splines and related approximations or viewing parameters of such designs as f- vectors of some convex polytopes and studying Hilbert Poincar\'e series for corresponding Cohen Maccalay rings, toric varieties or Erhart polynomials etc. Such alternative viewpoints will also be discussed.
On a strong multiplicity one property for the length spectra of even dimensional compact hyperbolic spaces.
Speaker:Chandrasheel Bhagwat (School of Maths, TIFR)
Time: Friday, 25th February, 2011, 2:30pm
Venue: AG-77
Abstract: I will talk about the length spectra of compact hyperbolic spaces and the Ruelle Zeta function associated to them. I will discuss some analytic properties of the Ruelle Zeta function and as an application, prove a strong multiplicity one property for even dimensional compact hyperbolic spaces. (This is a joint work with Prof. C. S. Rajan).
Hartshorne's Connectedness Theorem
Speaker:Anand Sawant (School of Maths, TIFR)
Time: Friday, 18th February, 2011, 2:30pm-3:45pm
Venue: AG-77
Abstract: We shall begin with a brief discussion of the algebraic and geometric aspects of the concept of dimension of a commutative ring. We shall then introduce the notion of depth of a ring and the notion of a Cohen-Macaulay ring. The Zariski topology on an algebraic variety has special features near a Cohen-Macaulay point; for instance, such a point cannot lie on two irreducible components of different dimensions. Hartshorne's Connectedness Theorem puts a further restriction on the Zariski topology near a Cohen-Macaulay point. It says that a variety must be locally "connected in codimension 1" at a Cohen-Macaulay point, that is, removing a subvariety of codimension 2 or more cannot disconnect it.
If time permits, we shall discuss an application of this theorem to set-theoretic complete intersections.
Inviscid Burgers Equation
Speaker:K.T. Joseph (School of Maths, TIFR)
Time: Friday, 11th February, 2011, 2:30pm
Venue: AG-77
Abstract:Inviscid Burgers equation is the simplest model equation which exhibit shock waves and rarefaction waves as solutions. Solutions are not even continuous if initial data is smooth with compact support. Hence global solution is understood in the sense of distribution. I explain E.Hopf's work [1950] on the construction of global entropy weak solution using vanishing viscosity method.
On a conjecture of Pomerance
Speaker:N. Saradha (School of Maths, TIFR)
Time: Friday, 4th February, 2011, 2:30pm
Venue: AG-77
Abstract:Let $k > 1$ be any integer. We say that $k$ is a P-integrer if the first $\phi(k)$ primes coprime to $k$ form a reduced residue system $\mod k$. It was conjectures by Pomerance that if $k$ is P-integer, then $k \leq 30$. We shall discuss this conjecture and the latest results towards this conjecture.
Mixed volumes and Alexandrov-Fenchel's inequality
Speaker:Amitava Bhattacharya (School of Maths, TIFR)
Time: Friday, 28th January, 2011, 4pm
Venue: AG-77
Abstract:Let $A_1,A_2,\ldots ,A_k$ be convex compact sets in ${\mathbb R}^n$. The sum $\sum_{i=1}^k \lambda_i A_i$ for $\lambda_i \ge 0 \forall i\in [k]$, is the set $S=\{\sum_i \lambda_i x_i \mid x_i\in A_i \forall i\in [k]\\}$. Minkowski showed that $Vol(S)$ is a homogeneous polynomial of degree $n$ in $\lambda_1,\lambda_2, \ldots ,\lambda_k$. In this talk we will see a proof (outline) of this statement and some of its interesting applications.
p-adic families of modular forms
Speaker:Ganesh (School of Maths, TIFR)
Time: Friday, 21st January, 2011, 2.30pm
Venue: AG-77
Abstract: Modular forms are one of the fundamental objects in Number theory. Hida
observed that modular forms are not discrete and they are related in a "continuous" way. In this talk, I will explain the meaning of "continuous" and their importance, and finally mention some examples.
Finite reflection groups are Coxeter groups
Speaker:R Venkatesh (School of Maths, TIFR)
Time: Friday, 14th January, 2011, 2.15pm to 3.45pm
Venue: AG-77
Abstract: In this talk we will show that finite reflection groups are Coxeter groups. In particular, this shows that the Weyl group of a root system is a Coxeter group. The talk will be accessible to all.
Congruent Numbers
Speaker:Somnath Jha (School of Maths, TIFR)
Time: Friday, 7th January, 2011 at 2:30 pm
Venue: AG-77
Abstract: A positive integer is a congruent number if it is the area of a right angled triangle with rational sides. We will unfold the story of classifying congruent numbers which goes back to 1000 years (and is still unsolved !). We will connect it to the Birch & Swinnerton-Dyer conjecture and Iwasawa Theory.
Constructing lattices in PSl_2(R) and PSl_2(C)
Speaker:Mahan Mj (Ramakrishna Mission, Belur)
Time: 31/12/2010 (Friday) at 2:30 pm to 3:30 pm
Venue: AG-77
Abstract: We shall describe some geometric constructions of lattices in PSl_2(R) and PSl_2(C). If time permits we shall describe the parametrization space (the Teichmuller space) of lattices in PSl_2(R) associated to a surface of genus g.
Flat connections and local systems
Speaker:Ronnie M. Sebastian (School of Maths, TIFR)
Time: 24/12/2010 (Friday) at 2:30 pm to 3:30 pm
Venue: AG-77
Abstract: Let $E\to X$ be a smooth vector bundle over a smooth manifold. We can describe this bundle by specifying a collection transition function. When does this bundle admit transition functions which are locally constant? If it does, then it is called a local system.
We can always put a connection on the bundle $E$. To any connection we can associate a $n\times n$ matrix of one forms. If this matrix is 0, then we say that the connection is flat.
If a bundle admits a flat connection, then it is a local system. This is the main result I want to prove in my talk.
A nice result of Kunze
Speaker:Anjan Gupta (School of Maths, TIFR)
Time: 21/12/2010 (Tuesday) at 2:00 pm to 3:30 pm
Venue: AG-77
Abstract:In this talk we shall discuss one of the paper of E Kunze which says that almost complete intersection ring is never Gorenstein.In this connection we shall introduce the notion of complete intersection ring, almost complete intersection ring, gorenstein ring, canonical module, maximal cohen macaulay module and many more(if time permits).
Deformations of group representations and differential forms
Speaker:Sudhanshu Shekhar (School of Maths, TIFR)
Time: 10/12/2010 (Friday) at 2:30 pm to 3:30 pm
Venue: AG-77
Abstract:In this talk I want to discuss about Deformations of group representations and its relations with differential forms and group cohomology. If time permits we will also discuss how these can be used to derive few properties of certain Selmer groups.
Complete intersection rings
Speaker:Vijaylaxmi Trivedi (School of Maths, TIFR)
Time: 03/12/2010 (Friday) at 2:30 pm to 3:30 pm
Venue: AG-77
Abstract:In this talk we define a notion of complete intersection rings (which can be thought as next best rings after regular rings), then give a homogical characterization. We discuss some properties of such rings.
We dicuss an application to space curves (which relates the problem of a local-global C.I. to a problem of Serre about projective modules over polynomial rings).
Weak dimension of Gaussian Rings
Speaker:Viji Thomas (School of Maths, TIFR)
Time: 26/11/2010 (Friday) at 2:30 pm to 3:30 pm
Venue: AG-77
Abstract: We will prove basic facts about Gaussian rings and introduce weak dimension of rings. We will prove that a domain is Gaussian iff it is Prufer.
Introduction to Connections
Speaker:Sudarshan Gurjar (School of Maths, TIFR)
Time: 19/11/2010 (Friday) at 2:30 pm to 3:30 pm
Venue: AG-77
Abstract: I will motivate and explain the basic ideas that go into the theory of connections on vector bundles. I will then say a few things about the Chern-Weil theory for vector bundles. I will assume some basic familiarity with vector bundles.
Diophantine approximations
Speaker:T.N. Shorey (School of Maths, TIFR)
Time: 12/11/10 (Friday) at 2:00 pm.-3:30pm
Venue: AG-77
Abstract: I shall give some results on Diophantine approximations and point out their connection with Diophantine equations and transcendence.
Canonical dimension of a quadric
Speaker:Anand Sawant (School of Maths, TIFR)
Time: 2.30 p.m, Friday, 29th Oct.2010.
Venue: AG-77
Abstract: The main object of this lecture is a quadric, which is the zero-set of a quadratic form in a suitable projective space. Starting with a brief introduction to the algebraic theory of quadratic forms, we shall introduce the "canonical dimension" of a quadric, which behaves better than the classical dimension with respect to splitting properties. We shall then discuss an algebraic and a geometric description of the canonical dimension.
Hecke Modifications of Bundles over Riemann Surfaces.
Speaker:Michael Lennox Wong (School of Maths, TIFR)
Time: 2.30 p.m, Friday, 22nd Oct. 2010.
Venue: AG-77
Abstract: A Hecke modification of a holomorphic vector or principal bundle over a Riemann surface is another bundle obtained by twisting the transition function of the original bundle in the neighbourhood of a point. The relationship with loop groups will be discussed, and if time permits, the relation to moduli of bundles. Definition and review of necessary concepts will be given as dictated by the needs of the audience.
The Hurwitz formula
Speaker:Gerald Gotsbacher (School of Maths, TIFR)
Time: 2.30 p.m, Friday, 15th Oct. 2010
Venue: AG-77
Abstract: Abstract: Given a Riemann surface $Y$ and a finite set of points $b_1,...,b_w$ on it Hurwitz asked the question of determining all n-sheeted coverings $f:X->Y$ ramified at the given points as well as their genus. The talk will revolve around different versions of the formulae he found.
Platonic solids, hypergeometric series, Kleinian singularities, Lie groups and catastrophe theory
Speaker:Alok Kumar Maharana (School of Maths, TIFR)
Time: 2.30 p.m, Friday, 8th Oct. 2010
Venue: Maths Seminar Room (A- 369)
Abstract: Five polyhedra in real three-space have attracted special interest since ancient times because of their regularity. Plato describes them in his dialogue "Timaios" and thus they were called Platonic solids. They are however attributed to Theaetetus and Pythagoreans by Euclid and it is believed that his Elements are directed towards the goal of deriving Theaetetus' classification in the final book XIII. More than two thousand years later these regular solids were involved in the development of new mathematical ideas. This talk will be a semi-historical/mathematical survey of how the classification of Platonic solids got related to ("is the same as") the classification of certain hypergeometric series, Kleinian singularities and simple Lie groups through the works of Schwarz, Klein, Arnold, Artin, Brieskorn and others.
The Weil Conjectures
Speaker:V. Srinivas (School of Maths, TIFR)
Time: 3.00 PM, Friday, 24 Sept 2010
Venue: AG77
Abstract: his talk will give an introduction to the Weil Conjectures, accessible to students, with some elementary examples used to motivate the conjectures.
Introduction to Moduli Spaces
Speaker:Amit Hogadi (School of Maths, TIFR)
Time: 2.30 PM, Tuesday, 14 Sept 2010
Venue: AG77
Abstract: This is an introductory talk on Moduli spaces in algebraic geometry.
(No Title)
Speaker:Vineeth Reddy (School of Maths, TIFR)
Time: 2.30 PM, Tuesday, 7 Sept 2010
Venue: AG77
Abstract: Jacobson proved that if all the elements of a ring satisfy the equation $x^n(x) = x$ for some n(x) > 1 depending on x, then the ring is commutative. What can we say about the number of solutions of $x^n = x$ in a finite noncommutative ring?
We give a bound for the maximum number of solutions of $x^p = x$(p is prime) in rings of order $p^n$. Interestingly we are able to characterize all such rings in which the bound is attained.
Higher Homotopy Group
Speaker:Devika Sharma (School of Maths, TIFR)
Time: Tuesday (22/06/2010), 2:30pm
Venue: AG77
Abstract: In the talk titled "Higher homotopy groups", we will start by briefly recalling the definition, group structure and a few properties of the fundamental group of a given topological space X. We then generalize the idea and define the higher homotopy groups of X, giving in detail the group structure and its properties. We will encounter that πn(Sn) = Z and πk(Sn) = {1} if k < n and see how a short exact sequence of a fiber bundle that satisfies the lifting criterion gives rise to a long exact sequence of homotopy groups and use it to calculate π3(S2). If time permits, I will state "The Blaker- Massey theorem" that will give us another tool to calculate the homotopy groups of a space and discuss a few examples based on it. The talk is intended to be well within the reach of the VSRP students.
A Property Testing based Streaming Algorithm for Checking whether Brackets are matched
Speaker:Girish Varma (STCS, TIFR)
Time: Tuesday (15th June, 2010), 2:30pm-3:15pm
Venue: AG77
Abstract: Property Testing about checking whether a long string over some finite alphabet satisfies a particular property or is far from any string that satisfies the property in hamming distance with a constant number of queries to different locations in the string. Considering multivariate on (m variables) polynomials over a finite field (F) as a long string with alphabet set F and length |F|^m, one can define a property which consist of just the zero polynomial. We will see that this property is testable, formalized by the Schwarz-Zippel Lemma. If time allows, we will also see an algorithm which makes one pass over the input data from left to right and uses only a small amount of space, for checking whether a string of brackets are well matched using this method.
Entropy in dynamical systems
Speaker:Siddhartha Bhattacharya (School of Maths, TIFR)
Time: Tuesday (25th May, 2010), 2:30pm
Venue: AG77
Abstract: In the context of dynamical systems one can introduce the concept of entropy in many ways. In this talk we will discuss some of these invariants and their applications.
The relationship of some classical results of Bernstein and Zelevinskii with the Langlands Reciprocity Law.
Speaker: Arnab Mitra (School of Maths, TIFR)
Time: 18th May 2010 (Tuesday), 2:30pm
Venue: AG77
Abstract: Abstract: Let W be the Weil group of a field F (a local non-archimedean field). By local class field theory there exists a natural bijection between the characters of W and those of F*, i.e. Gl(1,F). The reciprocity law generalizes this statement by connecting the n- dim representations of W with those of irreducible representations of Gl(n, F). Roughly speaking, in the talk i will show how some classical results of Bernstein et al can be used to extend the reciprocity law from the cuspidal case to all irreducible representations of Gl(n,F).
Maximum Principles in differential equations
Speaker: Anisa Chorwadwala (School of Maths, TIFR)
Time: Tuesday 4th May, 2010, 2:30pm
Venue: Math Seminar Room
Abstract: One of the most useful and best known tools employed in the study of partial differential equations is the maximum principle. This principle is a generalization of the elementary fact of calculus that any function $f(x)$ which satisfies the inequality $f'' >0$ on an interval $[a,b]$ achieves its maximum value at one of the endpoints of the interval. We say that the solutions of the inequality $f''>0$ satisfy a maximum principle. More generally, functions which satisfy a differential inequality in a domain $D$ and, because of it, achieve their maxima on the boundary of $D$ are said to possess a maximum principle. I will talk about certain maximum principles for second order elliptic differential operators.
Topological methods in combinatorics
Speaker: Saswata Shannigrahi (STCS ,TIFR)
Time: Tuesday, 27th April 2010, 2:30pm
Venue: Math Seminar Room
Abstract:Around 30 years ago, a new research area in combinatorics started with a proof by Laszlo Lovasz. He proved a conjecture in graph theory (called Kneser's conjecture) using topological methods. In this talk, I will present this proof and will also like to give an overview of this area of research.
Can we hear the shape of a drum?
Speaker: Chandrasheel Bhagwat (School of Maths, TIFR)
Time: Tuesday, 20th April 2010, 2:30pm
Venue: Math Seminar Room
Abstract:The title is a colloquial way to ask the following question: To what extent, one can determine the geometry of a manifold from its Laplace spectrum ? In this talk, I will give a brief introduction of the problem, and describe the results of Sunada, DeTurck, Gordon, and Berard which leads to answer above question in some specific cases and some conjectures.
A game of gambling and the Riemann Hypothesis
Speaker: Satadal Ganguly (School of Maths, TIFR)
Time: Tuesday, 13th April 2010, 2:30pm-3:30pm
Venue: Math Seminar Room
Abstract:I shall describe a betting game and explain how not lose money in it. I shall explicate the underlying number-theoretic principle which turns out to be equivalent to the Riemann Hypothesis on average.
A toy model for the Weil conjectures
Speaker: Arvind Nair (School of Maths, TIFR)
Time: Tuesday, 5th April 2010, 2:30pm-3:30pm
Venue: Math Seminar Room
Abstract:I will discuss a toy model for the Weil conjectures in the context of smooth manifolds with a special type of self-map. I will assume some basic knowledge of homology and cohomology and a little bit about smooth manifolds. (It is not necessary to know what the actual Weil conjectures are to follow the talk and I will say a little bit about the relation/analogy if time permits.)
The Jacobian Conjecture: A survey of developments
Speaker: Sagar Kolte (School of Maths, TIFR)
Time: Thursday, 30th March 2010, 2:30pm-3:30pm
Venue: AG-77
Abstract:I will state the conjecture and discuss the various equivalent formulations and partial results in the direction of this conjecture. I will also mention the related (and solved) Epimorphism theorem of Abhyankar and Moh.
Simplicial Objects: Outline, and an application to schemes
Speaker: Vaibhav Vaish (School of Maths, TIFR)
Time: Tuesday, 23rd March 2010, 2:30pm-3:45pm
Venue: AG-77
Abstract: In topology, simplicial sets are used as a "combinatorial model" for a wide class of topological spaces - the simplicial complexes - covering essentially all the spaces of natural interest. We will first discuss this model with a view that allows us to move from "sets" to an arbitrary "category". This part is abstract nonsense -- it's use is understood only when applied to specific contexts (that is to an specified "category" of interest). However, in that it requires few prerequisites, it should be accessible to everyone.To move towards some usage, we will also discuss a closely related (but more manageable) construct of so call "cubical" sets.
For the second part, we will assume definition of varieties (the whole description will work also with analytic spaces if one is only interested in those). Using that we will attempt to explain a useful result of Guillén-Navarro that allows us to compute fairly general constructions for singular varieties, if we know them already for smooth varieties. It is a variant of the method used by Deligne to prove existence of mixed hodge structure on cohomology of arbitrary varieties, and can be used to deduce several useful results.
If time permits (unlikely) we will discuss the full result of Guillén-Navarro, otherwise, we will content ourselves with stating and proving a key result on the way which may be of independent interest (and gives an idea of why the whole thing works).
p-adic L-functions and Iwasawa theory, from construction to application
Speaker: Ali Sanjari (Sharif University of Technology, Iran)
Time: Thursday, 18th March 2010, 2:30pm-3:30pm
Venue: AG-77
Abstract: Using interpolation and starting with Bernoulli numbers,posed by Leopold and Kubota, the p-adic L-function was constructed as the p-adic analogue of the Dirichlet L-functions. After that, Iwasawa found a new method for constructing these functions by using Stickelberger's elements.
In this talk we will try to explain a selection of these investigations around p-adic L-functions and Iwasawa theory with direction to their application in algebraic number theory and especially in finding a formula to compute the class number of some cyclotomic fields.
The Cayley Bacharach theorem
Speaker: Vivek Mallick (IMSc, Chennai)
Time: Tuesday , 9/03/10, 2:30pm-3:30pm
Venue: AG - 77
Abstract: There is a classical theorem which says that suppose C and D are two cubics on $\mathbb{P}^2$ which intersect at nine (different) points. Then any cubic passing through eight of the intersection points has to pass through the ninth one. We try to study some generalizations of this result. (may be I should also include "Best of luck" :D )
Higher dimensional local fields (Continuation Talk)
Speaker: Supriya Pisolkar (School of Maths, TIFR)
Time: Tuesday , 9/03/10, 11:30am-12:30am
Venue: Seminar Room
Abstract:
Higher dimensional local fields
Speaker: Supriya Pisolkar (School of Maths, TIFR)
Time: Friday 5/03/10, 2:00pm-3:00pm
Venue: Seminar Room - A 369
Abstract: A very interesting direction of generalizations of class field theory is to develop a theory for higher dimensional fields. One of the first ideas in higher class field theory is to work with Milnor K-groups instead of multiplicative groups. Higher local class field theory contains classical local class field theory as 1-dimensional version.
I will first recall important notions/statements in local class field theory (1-dimensional case). Then we will see some basic notions for higher dimensions. I won't be going into the details of class field theory in this case , and thus this talk will be very elementary.
Measuring Randomness
Speaker: Sarang Sane (School of Maths, TIFR)
Time: Tue, 23rd Feb, 2:30pm-3:30pm
Venue: AG-77
Abstract: Consider throwing a "fair" coin as opposed to throwing a coin with two heads. It is natural to think that the experiment/action/event of throwing a "fair" coin is "more random" than that of throwing the coin with two heads. This takes us to the natural question of whether we can somehow measure randomness.
For the major portion of this talk, we will try to answer the question, "How random is this action/event/experiment/phenomenon"? This part is intended to be elementary, precise and completely self-contained. The answer will be an expression which occurs in many other contexts as well. Towards the end, I will try and make an ambitious attempt to try and tie this up with applications in science (this part might be very vague).
Proofs of Godel's theorem (Continuation Talk)
Speaker: Nitin Nitsure (School of Maths, TIFR)
Time: Fri, 19th Feb, 2:30pm-3:30pm
Venue: AG-77
Abstract: This lecture will focus on explaining three different proofs of G\"odel's first incompleteness theorem: the semantic proof, the syntactic proof, and the computability proof. The main technical points are the diagonalization argument, the G\"odel encoding and the basics of primitive recursion.
Grothendieck's splitting theorem for vector bundle on projective line
Speaker: Sanjay Kumar Singh (School of Maths, TIFR)
Time: Tue, 16th Feb, 2:30pm-3:30pm
Venue: AG-77
Abstract: I will try to explain all definitions and results needed to prove the theorem. I will give definition of a divisor and a vector bundle,and the correspondence between line bundles and divisors, and then finally give proof of the main theorem.
Langlands functoriality principle
Speaker:Debargha Banerjee (School of Maths, TIFR)
Time:Tue, 9th Feb, 2:30pm-3:30pm
Venue:AG-77
Abstract: In this talk, I will try to explain the concept of dual groups and functoriality principle. We will try to understand the functoriality in the simplest possible examples. We will give emphasis on the particular examples like base changes and adjoint lifts.
Mathematics and Logic
Speaker:Nitin Nitsure (School of Maths, TIFR)
Time: Tue, 2nd Feb, 2:30pm-3:30pm
Venue: AG-77
Abstract:
Tate Curves
Speaker:Somnath Jha (School of Maths, TIFR)
Time: Fri, 29th Jan, 2:00pm-3:15pm
Venue: AG-77
Abstract: An elliptic curve over C can be viewed as C/Λ for some lattice Λ in C. Tate has fomulated analogous description for elliptic curves over p-adic number fields with non-integral j-invariant. Starting from the definition of elliptic curve we will give an overview of the structure of elliptic curves over the field of Complex Numbers, Real Numbers and then talk about the Tate parametrisation of elliptic curves over p-adic number fields
On the Shafarevich Conjecture and Genus 2 fibrations
Speaker:R.V.Gurjar (School of Maths, TIFR)
Time: Tue, 19th Jan, 2:30pm
Venue: Seminar room
Abstract: The famous shaferavich conjecture asserts that the universal cover of a smooth projective variety over complex numbers is holomorphically convex, that is given any sequence of points going to infinity in the universal cover there is a holomorphic function which is unbounded on that sequence. This conjecture is the correct generalization of the uniformization theorem of Riemann. I will talk about the conjecture in general, the known cases when the conjecture is proved, its consequences which I have proved, and my results with Shastri and Purnaprajna.